Phase Equilibria and Crystal Chemistry in Portions of the System SrO-CaO-Bi₂O₃-CuO, Part IV— The System CaO-Bi₂O₃-CuO

Abstract

New data are presented on the phase equilibria and crystal chemistry of the binary systems CaO-Bi₂O₃ and CaO-CuO and the ternary CaO-Bi₂O₃-CuO. Symmetry data and unit cell dimensions based on single crystal and powder x-ray diffraction measurements are reported for several of the binary CaO-Bi₂O₃ phases, including corrected compositions for Ca₄Bi₆O₁₃ and Ca₂Bi₂O₅. The ternary system contains no new ternary phases which can be formed in air at ~700–900 °C.

1. Introduction

The discovery of superconductivity in cuprates by Bednorz and Müller [1], and its confirmation by Takagi et al. [2] as being due to the phase La_2−xBa_xCuO₄, led to a world-wide search for other compounds with higher T_c’s. Identification of the superconducting phase Ba₂YCu₃O_6+x [3], with a critical temperature T_c ~90 K [4], has resulted in hundreds of published reports on the properties of this and related phases.

Phases with still higher T_c’s were found in the systems SrO-CaO-Bi₂O₃-CuO and BaO-CaO-Tl₂O₃-CuO [5,6]. These phases belong mostly to a homologous series A₂Ca_n−1B₂Cu_nO_2n+4 (A=Sr, Ba; B = Bi, Tl). In the Bi⁺³ containing systems a phase with n =2 and T_c ~80 K is easily prepared. The exact single-phase region of this phase is not well known, and a structure determination has not been completed because of very strong incommensurate diffraction that is apparently due to a modulation of the Bi positions. Higher n (and higher T_c) phases have not been prepared as single-phase bulk specimens (without PbO). We undertook a comprehensive study of phase equilibria and crystal chemistry in the four component system SrO-CaO-Bi₂O₃-CuO in the hope that such a study will define the optimum processing parameters for reproducible synthesis of samples with useful properties.

A prerequisite to understanding the phase equilibria in the four component system is adequate definition of the phase relations in the boundary binary and ternary systems. The ternary system SrO-CaO-CuO was the first to be investigated [7,8], followed by the ternary system SrO-Bi₂O₃-CuO and its binary subsystems [9,10,11,12]. Preliminary versions have been published of the systems CaO-Bi₂O₃-CuO and SrO-CaO-Bi₂O₃ [13], and the details of the system SrO-CaO-Bi₂O₃ will appear in the near future [14]. The experimental details, phase relations, and crystal chemistry of the binary CaO-Bi₂O₃ and the ternary system CaO-Bi₂O₃-CuO are the subject of this publication.

In the following discussion of phase equilibria and crystal chemistry, the oxides under consideration will always be given in the order of decreasing ionic radius, largest first, e.g., CaO:1/2Bi₂O₃:CuO. The notation 1/2Bi₂O₃ is used so as to keep the metal ratios the same as the oxide ratios. The “shorthand” notation is used to designate the phases with C = CaO, B = 1/2Bi₂O₃ and Cu=CuO. Thus compositions may be listed simply by numerical ratio e.g., the formula Ca₄Bi₆O₁₃ can be written as C₂B₃ or simply 2:3.

2. Experimental Procedures

In general, about 3.5 g specimens of various compositions in binary and ternary combinations were prepared from CaCO₃, Bi₂O₃ and CuO. Neutron activation analyses of the starting materials indicated that the following impurities (in μg/g) were present: in CuO-3.9Cr, 2.8Ba, 28Fe, 410Zn, 0.09Co, 1.9Ag, 0.03Eu, 14Sb; in Bi₂O₃-2.1Cr, 0.0002SC, 26Fe, 21Zn, 0.6Co, 0.5Ag, 0.0008Eu, 0.2Sb; in CaCO₃-1.1Cr, 6Ba, 160Sr, 0.0001Sc, 5Fe, 14Zn, 0.14Co, 0.01Ag, 0.0005Eu, 0.02Sb. The constituent chemicals were weighed on an analytical balance to the nearest 0.0001 g and mixed either dry or with acetone in an agate mortar and pestle. The weighed specimen was pressed into a loose pellet in a stainless steel dye and fired on an MgO single crystal plate, or on Au foil, or on a small sacrificial pellet of its own composition. The pellets were then calcined several times at various temperatures from ~600 to 850 °C, with grinding and repelletizing between each heat treatment. Duration of each heat treatment was generally about 16–20 h. For the final examination a small portion of the calcined specimen was refired at the desired temperature (1–8 times), generally overnight, either as a small pellet or in a small 3 mm diameter Au tube, either sealed or unsealed. Too many heat treatments in the Au tube generally resulted in noticeable loss of Cu and/or Bi.

When phase relations involving partial melting were investigated, specimens were contained in 3 mm diameter Au or Pt tubes and heated in a vertical quench furnace. This furnace was heated by six MoSi₂ hairpin heating elements with a vertical 4 in diameter ZrO₂ tube and a 1 in diameter Al₂O₃ tube acting as insulators. The temperature was measured separately from the controller at a point within approximately 1 cm of the specimen by a Pt/90Pt10Rh thermocouple, calibrated against the melting points of NaCl (800.5 °C) and Au (1063 °C). After the appropriate heat treatment, the specimen was quenched by being dropped into a Ni crucible, which was cooled by He flowing through a copper tube immersed in liquid N₂.

In order to approach equilibrium phase boundaries by different synthesis routes, many specimens were prepared from pre-made compounds or two phase mixtures as well as from end members. These were weighed, mixed, and ground in the same way as for the previously described specimens. Also, some specimens were: 1) annealed at temperature (T₁) and analyzed by x-ray powder diffraction; 2) annealed at a higher or lower temperature (T₂) where a different assemblage of phases was observed; 3) returned to T₁ to demonstrate reversal of the reaction(s) between T₁ and T₂. All experimental details are given in Tables 1a and 1b. Phase identification was made by x-ray powder diffraction using a high angle diffractometer with the specimen packed into a cavity 0.127 or 0.254 mm deep in a glass slide. The diffractometer, equipped with a theta compensator slit and a graphite diffracted beam monochromator, was run at 1/4° 2 θ/min with CuKα radiation at 40 KV and 35 MA. The radiation was detected by a scintillation counter and solid state amplifier and recorded on a chart with 1°/2 θ = 1 in. For purposes of illustration and publication, the diffraction patterns of selected specimens were collected on a computer-controlled, step scanning goniometer and the results plotted in the form presented.

Table 1a.

Experimental data for the system CaO-Bi₂O₃-CuO

Spec. no.		Composition mole percent			Heat treatmentb temp °C		Phys. obser.c	Results of x-ray diffractiond
	CaO	1/2Bi2O3	CuO	Initial	final	Time h
	100	0	0
				500				CaCO3
				600				CaO+CaCO3
				600×2				CaO
	66.7	0	33.3
				700
				850
				1000×3				C2Cu
	60	0	40
		nitrates		500				CaO+CuO
					750	48		CaO+CuO+C1−xCu
					$\begin{array}{c}700\\ 800\end{array}\}$	$\begin{array}{c}24\\ 12\end{array}\}$		CuO+CaO+C2Cu
				750×2
					900			C2Cu+CuO
					745	2.0−O2		C2Cu+CuO
					$\begin{array}{l}800\hfill \\ 875\times 2\hfill \end{array}\}$			C2Cu+CuO
					950			C2Cu+CuO
					980	16		C2Cu+CuO
					990	0.66		C2Cu+CuO+CCu2
					990	14.0		C2Cu+CCu2
					1000			C2Cu+CCu2
					1000×2			C2Cu+CCu2
					10000×3			C2Cu+CCu2
					1007	0.16
					1011	1.0		C2Cu+Cu2O+CCu2
					1014	0.5		C2Cu+Cu2O
	50	0	50
#1		ppt. hydrox-carb.		450
					740	6.0		C1−xCu+CaO+CuOtr
					740	15.0		C1−x, Cu+CaO
				740				C1−xCu+CaO
					800	16.0		C2Cu + CuO
#2		ppt. hydrox-carb.		500				CuO+C1−xCu
					550			CuO+C1−xCu + CaO
					600			C1−xCu+CaO+ CuO
					650			C1−xCu+CuO+CaO
					700			C1−xCu+CuO+Ca(OH)2
					740			C1−xCu+CaO+CuO
					740	62.5		C1−xCu+CaO+C2Cutr
					760			C1−xCu+CaO+CuO
					780			C1−xCu+CaO+CuO
					800			C1−xCu+CaO+CuOtr
#3				600				CuO+CaO+CaCO3+C1−xCu
				600×2				CuO+CaO+CaCO3+C1−xCu
				600×3				CuO+CaO+CaCO3+C1−xCu
				600×4				CuO+CaO+CaCO3+C1−xCu
				675				CuO+CaO+C1−xCu
				675×5				C1−xCu+CaO+CuO
				675×11				C1−xCu+CaO+CuO
				675×16				C1−xCu+CaO+CuO
				675×21				C1−xCu+CaO+CuO
				675×26				C1−xCu+CaO+CuO
				675×31				C1−xCu+CaO+CuO
				675×36				C1−xCu+CaO+CuO
				750×2				CaO+CuO+C2Cu
				850				CaO+CuO+C2Cu
				900				C2Cu+CuO+CaO
				600
				750
				900				C2Cu+CuO+CaO
					675	70		C2Cu+CuO+CaO
					675×4			C2Cu+CuO+CaO
#4		nitrates		500
				600
					995	1.0		C2Cu+CuO+CCu2
					1007	10.0		C2Cu+CCu2+Cu2O
					1011	1.0		C2Cu+Cu2O+CCu2
					1013	1.0		C2Cu+Cu2O+CCu2tr
					1007 1013	$\begin{array}{l}10\hfill \\ 24\hfill \end{array}\}$		C2Cu+Cu2O+CuO+CCu2tr
					1014	0.5		C2Cu+Cu2O+CuO+CCu2tr
					1018	0.5		C2Cu+Cu2O+CuO+CCu2tr
					1022	0.5	n.m.	C2Cu+Cu2O+CuO+CCu2tr
					1028	0.5	p.m.	C2Cu+Cu2O+CCu2tr
					1032	0.5	p.m.	C2Cu+Cu2O+CCu2tr
					1036	0.5	p.m.	CaO+C2Cu+Cu2O+CCu2tr
					1040	0.5	p.m.	CaO+C2Cu+Cu2O+CCu2tr
#5		citrates			700	22		C1−xCu+CaO
					700	18−O2		C1−xCu+CaO
	47.37	0	52.63
		(9:10)
		citrates			700	18		C1−xCu+CaO
					700	78−O2		C1−xCu+CaO
	45.45	0	54.54
		(5:6)
		citrates			700	18		C1−xCu
					700	21−O2		C1−xCu+CaO
					700	39−O2		C1−xCu+CaO
					700	78−O2		C1−xCu+CaO
	45.33	0	54.67
		citrates			700	86−O2		C1−xCu
	45.20	0	54.80
		citrates			700	16
					700	24−O2		C1−xCu
	44.95	0	55.05
		citrates		700	16
					700	24−O2		C1−xCu+CuOtr
	44.70	0	55.30
		titrates		700	16
					700	24−O2		C1−xxCu+CuO
	40	0	60
		citrates		700	60			C1−xCu+CuO
				700	18−O2			C1−xCu+CuO
				800
	33.3	0	66.7
				800
				875×2				C2Cu+CuO
					965	25.0		C2Cu+CuO
					1000	19.0		CCu2+C2Cu+CuO
					1000×2			CCu2+C2Cu+CuO
	30	0	70
#1		nitrates		500				CuO+CaO
				750				CuO+CaO
				770				CuO+CaO
				750×2				CuO+CaO+C2Cu
				990				CuO+C2Cu
				500
					980	16.0		CuO+C2Cu
					990	22.0		CCu2+CuO+C2Cu
					1000	16.0		CCu2+Cu2Otr+C2Cutr
					1010	0.5		CCu2+Cu2O+C2Cutr
					1014	0.5		Cu2O+C2Cu+CCu2
					1016	24.0		Cu2O+C2Cu+CCu2tr
#2		citrates			700	86−O2
	25	0	75
#1				600
				750
					950			CuO+C2Cu
					975			CuO+C2Cu
					1000			CCu2+CuO+Cu2O+C2Cu
					1025			Cu2O+C2Cu+CuO
#2		nitrates			450
				500
				600				CuO+CaO
					750	72−O2		CuO+C1−xCu
					770	48−O2		CuO+C1−xCu
					780	68−O2		CuO+C1−xCu
					790	30−O2		CuO+C1−xCu+CaOtr
					800	36−O2		CuO+C1−xCu
					820	42−O2		CuO+C1−xCu
					830	72−O2		CuO+C1−xCu+C2Cutr
					840	36-O2		CuO+C1−xCu+C2Cu
					880	36−O2		CuO+C2Cu
					750	54		CuO+CaO+C1−xCu
					760	120		CuO+C2Cu
					780	120		CuO+C2Cu
					800	20		CuO+C2Cu+CaO
					840	64		CuO+C2Cu
					1012	1.0	p.m.	Cu2O+C2Cu+CCu2
					1020	0.5	p.m.	Cu2O+C2Cu+CCu2+CaO
	20	0	80
		nitrates		500
				600
					1007	1.0		CuO+CCu2+Cu2Otr
					1011	1.0		CCu2+Cu2O+CuO
					1014	0.16	p.m.	CCu2+Cu2O+CuO
					1016	0.5	p.m.	Cu2O+C2Cu+CuO+CCu2
					1020	0.5	c.m.	Cu2O+C2Cu+CuO+CCu2
	15	0	85
		nitrates		500
				600	1016	0.16	p.m.	CuO+Cu2O+CCu2
					1020	0.33	c.m.	Cu2O+CuO+CCu2
	10	0	90
		nitrates		500
				600	1020	0.16	p.m.	Cu2O+CCu2+CuO
	5	0	95
		nitrates		500
				600	1016	0.16	p.m.	CuO+Cu2O+CCu2
					1020	0.16	p.m.	CuO+Cu2O+CCu2
	10	90	0
				700
				750				rhomb+fcc′
					850	0.33	s.m.	rhomb+fcc′+fcc″
					860	0.33	p.m.
					870	0.33	c.m.	fcc′+rhombtr
	20	80	0
				700
				750				rhomb
					650			rhomb
					835	0.33		rhomb+fcc′
					875	0.33	s.m.	rhomb+fcc′
					875	0.66	s.m.	rhomb+fee′
					890	0.33	c.m.	rhomb+fcc′
					$\begin{array}{l}700\to 875\hfill \\ 875\to 650\hfill \end{array}\}$	at 3°/h		rhomb+C5B14
					$\begin{array}{l}750\to 870\hfill \\ 870\to 845\hfill \end{array}\}$	at 1°/h		rhomb
	23	77	0
				700				rhomb+C2B3
				800				rhomb+C2B3
					840	0.5	fcc′
					870	0.33	n.m.	fcc′
					880	0.33	n.m.	fcc′+rhomb
					880	0.33	n.m.	fcc′
					890	0.33	cm.	fcc′
				850
				750×2				rhomb
	25	75	0
				700
				750				rhomb+CB2+C5B14
					650	16		rhomb+C5B14
					750	1		rhomb
					780	0.5		rhomb
					800	1		rhomb
					950	1.2	c.m	fcc′
				850				rhomb
				750×2				rhomb
	26	74	0
				700
				750				rhomb+C2B3
					820	0.33	n.m.	fcc′+rhombtr
					880	0.33	p.m.	fcc′+bcctr
					890	0.33	cm.	fcc′
	26.32	73.68 (5:14)	0
#1				750
				650				C5B14+rhomb+C2B3
					750	16		rhomb+C2B3+C5B14
					1000	1.75	c.m.	fcc′+bcctr
					650			C5B14
#2				650×2				rhomb+C2B3+CB2
				650×5				rhomb+CB2+C5B14
				750×3				rhomb+C5B14+CB2tr
#3				750				rhomb+C2B3
				750×2
				925		0.33	c.m.	fcc′
				750×3				rhomb+CB2+C5B14
					925	0.33	c.m.	fcc′
					1000	1.0	c.m.
					650	16		C5B14
					650	336		C5B14
				750×5				rhomb+CB2+C5B14
					700	100 MPa		rhomb
	27.27	72.72 (3:8)	0
				750
					650			rhomb+CB2+C2B3+C5B14
				750×5				CB2+C5B14+rhomb
					750	16.0		CB2+rhomb+ C5B14
				850
				750×2				C5B14+CB2+rhombtr
	28	72	0
				700
				750
					860	0.33		fcc′
					870	0.33	n.m.	fcc′
					880	0.33	p.m.	fcc′
					900	0.66	c.m.	fcc′
	30	70	0
				750
					650			CB2+C5B14+C2B3+rhomb
				750×5				CB2+C5B14+rhomb
					750	1.33		CB2+C5B14+rhomb
				850
				750×2				CB2+C5B14+rhomb
	33.33 (1:2)	66.67	0
#1				800
				1000	0.166		c.m.
				750				C2B3+C5B14+CB2
					750	16.0		C2B3+C5B14+rhomb
#2				700
				750				CB2+C5B14+C2B3+rhomb
					65	96		CB2+C5B14+C2B3
					850	16		fcc′+bcctr
				800				fcc′+C2B3
				850
				750×2				CB2+rhomb+C5B14
				1000		1.75	c.m.	fcc′+bcctr
				650		16		CB2+C2B3tr
#3				750×5				CB2+rhomb+C2B3tr
					750	1.33		CB2+rhomb
					$\begin{array}{l}925\hfill \\ 700\hfill \end{array}\}$	0.13 312	c.m.	CB2+C2B3†
					$\begin{array}{l}1000\hfill \\ 650\hfill \end{array}\}$	1.0 17	c.m.	CB2+C5B14+C2B3
				650×4
				650×5				CB2+C2B3tr+C5B14tr
				700				CB2+C5B14+C2B3tr
				750×3				CB2
				750				C2B3+rhomb
				750×3				CB2+C2B3tr
				750×5				CB2+C2B3tr
					650 100 MPa			CB2+C2B3
#5	lactate			450
				650×3				CB2+C5B14
				650×4				CB2+C5B14
					700			CB2+C5B14
					750			CB2+C2B3+rhomb+C5B14tr
	35	65	0	750				C2B3+rhomb+fcc
					770	60		C2B3+rhomb+fcc′
						780 0.33		C2B3+rhomb+fcc
					790	0.66		C2B3+fcc′+rhombtr
					820	0.33		C2B3+fcc′
					830	0.33		C2B3+fcc′
					830	8.0		C2B3+fcc′+bcctr
					840	0.33		C2B3+fcc′+bcctr
					840	13.0		bcc
					850	0.33		bcc+fcc′+unknown
					850	1.0		bcc
					920	0.16	p.m.	bcc+fcc′
	37.5	62.5 (3:5)	0
				750
				650				C2B3+CB2+C5B14
				750×5				C2B3+CB2
	40	60 (2:3)	0
#1				750
				650				C2B3+CB2+C5B14+CB+CaO
				750×5				C2B3
#2				750
				650
				750×5				C2B3
				800				C2B3
				850				C2B3
					900	1.0		bcc
#3				700
				700×5				C2B3
				850				C2B3
				900				bcc+C-mon+unknown
					750			C2B3
#4				700
				800
				900×2				C2B3+unknown
				750				C2B3
					700	240		C2B3
					875	16		bcc
					$\begin{array}{l}1000\hfill \\ 700\hfill \end{array}\}$	1.0 240		C2B3
#5				700
				850
				900×2
				825				C2B3
#6				700
				750
					860	0.33		bcc
					935	0.33	n.m.	bcc
					950	0.33	p.m.	bcc
	41.18	58.82 (7:10)	0
				750
				650				C2B3+CB2+CB+CaO
					825	17		C2B3+CB
					900	20		bcc+C-mon+fcc′
				750×5				C2B3+CB
	42.86	57.14 (3:4)	0
				700
				750
				850				C2B3+CB
	45	55	0
				700
				750				C2B3+CB+CB2+CaO
					650	96		C2B3+CB+CaO
					850	16		C2B3+CB+CaO
					870	0.66		bcc+CB
					890	0.33		bcc+C-mon+CB
					900	0.33		bcc+C-mon+CBtr
					900	1.00		bcc+C-mon
					940	1.00		bcc+CB+C-mon
					880	1.00
					950	0.33	p.m.	bcc+C-montr
					1000	1.75	c.m.	bcc
	48	52	0
				700
				800
				900				CB+bcc
					955	0.33		C-mon+bcc+CaO
					960	0.33		bcc+C-mon+CaO
					940	0.33
					970	0.33	p.m.	bcc+CaO
	50	50	0
#1				700
				750				CB+C2B3+CaO
					650	96		CB+C2B3+CaO
					850	16		CB+C2B3
					900	1.0		CB
				900
					940	1.0
					$\begin{array}{l}940\hfill \\ 820\hfill \end{array}\}$	2.0 15		C-mon CB+Czmon
					1000	1.0	c.m.	bcc+CaO
#2				750				C2B3+CB+CaO
					860	10.0		CB
					880	1.0		CB+unknown+CaO
					940	0.33		C-mon
					940	2.0		C-mon
					950	0.25		C-mon
					960	0.5	n.m.	C-mon+bcc+CaO
					970	0.33	p.m.	bcc+CaO
				940		2.0		C-mon
					850	3.0		C-mon
					880	11.0		CB
					$\begin{array}{l}1000\hfill \\ 940\hfill \end{array}\}$	0.16 24.0		bcc+CaO
#3				700
				800
				900				CB
				825				CB
					940			CB
				940				CB
#4				700
				750×4
				850				CB
				900				CB
	53.85	46.15 (7:6)	0
#1				750
				650				C2B3+rhomb+CB+CaO
				750×5				CB+CaO
#2				750
				650
				900				CB+CaO
#3				700
				800
				900				CB+CaO
				825				CB+CaO
					940	16.0		CB+CaO
	54	46	0
				750
				650
					930	2.0	n.m.	C-Mon+CaO
					940	2.0
					920	2.0		C-Mon+CaO
	57.14	42.86 (4:3)	0
				750
				850				CB+CaO+C2B3tr
				900				CB+CaO
	60	40	0
#1				900				CB+CaO
				900×2				CB+CaO
#2				750
				650				CB+C2B3+CaO
				750×5				CB+CaO
	66.67	33.33	0
				750×2				CB+CaO
					920	0.33	n.m.	CB+CaO
					930	0.33	n.m.	C-Mon+CaO
					940	0.33	n.m.	C-Mon+CaO
					950	0.33	n.m.	C-Mon+CaO
					960	0.33	n.m.	bcc+CaO
	71.43	28.57 (5:2)	0
				750×5				CB+CaO
	11.11	44.44	44.44
				700
				750				rhomb+CuO+B2Cu
				750×5				rhomb+CuO+B2Cu
	20	40	40
				700
				750				CuO+rhomb+CB2
				750×5				CuO+CB2+rhomb
	33.33	33.33	33.33
				700
				750				CB+C2B3+CuO
				750×5				CB+C2B3+CuO
	44.02	7.14	48.84
	Ca4Bi6O13+Ca2Bi2O5+C1−xCuO2
		1:1:10						C1−xCu+C2B3+CB
				700				C1−xCu+CB+C2B3
				700×2				C1−xCu+CB+C2B3tr
				700×3				C1−xCu+CB
				700×4				C1−xCu+CB
	44.44	22.22	33.33
	Ca2CuO3+Bi2CuO4
		2:1						C2Cu+B2Cu
				700				C2Cu+C2B3+B2Cu+CuO
				700×2				C2Cu+C2B3+B2Cu+CuO+CB
				700×3				C2Cu+C2B3+CuO+CB+B2Cue
	45	45	10
				700
				750
					920	0.33	p.m.	bcc+C-mon+CaO
					940	0.33	c.m.	bcc+CaO+C-montr
	49	49	2
				700
				750
					900	0.33		CB
					910	0.33		CB
					915	16.0	p.m.	CB
					930	0.33	p.m.	bcc+CaO
	50	25	25
				700
				750				CB+CuO+CaO
					800			CB+CuO+CaO
				750×5				CB+CuO+CaO
	54	23	23
				700
				750×6				CB+CaO+CuO+C1−xCu
	54.95	14.63	30.41
	Ca4Bi6O13+Ca2CuO3+C1−xCuO2
		1:7:3						C2B3+C2Cu+C1−xCu
				700				C2B3+C2Cu+C1−xCu+CB
				700×2				C2Cu+C1−xCu+CB+C2B3
				700×3				C2Cu+C1−xCu+CB+C2B3
	56	24	20
	Ca4Bi6O13+Ca2CuO3
		1:5						C2Cu+C2B3
#1				700				C2Cu+C2B3+CB
				700×2				C2Cu+C2B3+CB+CuO
				700×3				C2Cu+CB+C2B3+CuO
					700	O2		C2Cu+CB+C2B3+CuO
					750			C2Cu+CB+C2B3+CuOtr
#2					750×2			C2Cu+CB+C2B3+CuOtr
					750×2
					700	336		C2Cu+CB+CuOtr
#3	+C1−xCutr							CB+C2Cu+C2B3
#4	+C1−xCu(more)							CB+C2Cu+C2B3+C1−xCu
					700			CB+C2Cu+C2B3+C1−xCu
					700×2
					700×3f
					700×4f
					700×5f
	57.14	9.52	33.33
	Ca2CuO3+Bi2CuO4
	6:1							C2Cu+B2Cu
				700				C2Cu+B2Cu+C2B3+CuO
				700×2				C2Cu+C2B3+B2Cu+CuO
				700×3				C2Cu+CB+C2B3+CuO
	60	20	20
				700
				750				CB+CaO+CuO
				750×5				CB+CaO+Ca1−xCu+CuO
				750×9				CB+CaO+Ca1−xCu+CuO
	61.29	19.35	19.35
	Ca2CuO3+Ca7B6O16
		6:1		750×2				CB+C2Cu+CaO
					700	336		CB+C2Cu+CaOtr
	70	15	15
				700
				750×5				CaO+CB+Ca1−xCu+CuO
					800			CaO+CB+Ca1−xCu+CuO
					850			CaO+CB+C2Cu
					900			CaO+C-mon+C2Cu
					900
					750			CaO+CB+C2Cu
					$\begin{array}{l}900\hfill \\ 750\hfill \end{array}\}$			CaO+Czmon+C2Cu
					900×7,126

^aStarting materials CaCO₃, Bi₂O₃, CuO except when listed in italics. Compositions given in italics were formulated from the listed pre-reacted compounds or compositions.

^bSpecimens were given all previous heat treatments listed in the initial column, sequentially, and held at temperature 16–24 h, with grinding in between, for the number of times shown and then reheated at the final temperature for the indicated number of hours. (if hours are not specified heat treatment was overnight). O₂=heat treatment in one atmosphere of purified oxygen.

^cp.m. = partially melted, c.m. = completely melted, n.m. = no melting, s.m. = slightly melted.

^dCompounds are listed in order of estimated amounts, most prevalent first.

tr=trace, just barely discernable.

C₂Cu = Ca₂CuO₃

C_1−xCu = Ca_1−xCuO₂

CCu₂=CaCu₂O₃

rhomb=rhombohedral solid solution

fcc=face centered cubic solid solution; symmetry often distorted and generally with superstructure

fcc′-very slight rhombohedral distortion of cubic symmetry, with incommensurate superstructure perpendicular to the hexagonal c* (corresponding to α′, of [20].

fcc″-metastablephase with larger rhombohedral distortion of cubic symmetry, with superstructure equal to 42 and faint incommensurate superstructure perpendicular to the hexagonal [hOl] plane.

bcc=body centered cubic solid solution; symmetry often distorted and generally with superstructure.

C₅B₁₄ = Ca₅Bi₁₄O₂₆

CB₂=CaBi₂O₄

C₂B₃ = Ca₄Bi₆O₁₃

CB = Ca₂Bi₂O₅(triclimic)

C-mon = metastable C-centered monochnic phase near Ca₆Bi₇O_16.5.

^eAlthough Ca₄Bi₆O₁₃ has formed during first 700 °C heat treatment, further heating and grinding resulted in formation of Ca₂Bi₃O₅, which increased with the third heat treatment, indicating that the 2:3 phase was formed metastably but the 1:1 compound is the stable phase.

^fAmount of 2:3 decreasing and amount of Ca_1−xCuO₂ may be increasing very slightly.

Table 1(b).

Experimental conditions for crystal growth experiments

Charge	Flux	Container	Temperature cycle	Results
CaO:1/2Bi2O3 1:6	(KNa)Cl	Small dia Au sealed	700 °C 595 h	biaxial xtals Rhomb (Orth)
90 wt%	10 wt%
CaO:1/2Bi2O3 1:4		Small dia Au sealed	700→875 °C @ 10 °C/h 875→650 °C @ 3 °C/h
CaO:1/2Bi2O3 5:14	(KNa)Cl	Large dia Pt sealed	750 °C→645 °C @ 1 °C/h 645 °C 64 h
20 wt%	80 wt%
CaO:1/2Bi2O3 5:14	(KNa)Cl	large dia Pt	750 °C→645 °C @ 1 °C/h
20 wt%	80 wt%		645 °C 64 h
CaO:1/2Bi2O3 5:14	10μLH2O	Small dia Au sealed	Hydrothermal unit 700 °C 100 MPa
CaO:1/2Bi2O3 5:14	(KNa)Cl	Large dia Au sealed	650 °C→750 °C @ 10 °C/h
80 wt%	20 wt%		750 °C→640 @ 1 °C/h
CaO:1/2Bi2O3 5:14	None	Small dia Au open	900 °C, 20 min. quenched (liq N2 cooled He cup) crushed
		Small dia Au open	780 °C 67.5 h quenched (liq N2 cooled He cup)	fcc′
CaO:1/2B2O3 5:14	None	Small dia Au sealed	925 °C→850 °C @ 3 °C/h 850 °C 24 h quenched (liq N2 cooled He cup)	Ca5Bi14O26
		Small dia Au open	650 °C 2 weeks
CaO:1/2Bi2O3 5:14	None	Small dia Au sealed	925 °C→850 °C @ 3 °C/h
		Small dia Au open	650 °C 16 h
CaO:1/2Bi2O3 3:8	None	Small dia Au open	900 °C 22 h quenched (liq N2 cooled He cup) crushed
		Small dia Au open	−800 °C 3 d quenched (liq N2 cooled He cup)
			−760 °C 15 min pulled from furnace
			−800 °C 1 h quenched (liq N2 cooled He cup)
			−760 °C 10 min quenched (liq N2 cooled He cup)	fcc″
CaO:1/2Bi2O3 33:67	(KNa)Cl	Small dia Au sealed	775 °C (18h)→645 °C @ 1 °C/h
80 wt%	20 wt%
CaO:1/2Bi2O3 33:67	(KNa)Cl	Small dia Au sealed	775 °C(18h)→645 °C @ 1 °C/h	CaBi2O4
20 wt%	80 wt%
CaO:1/2Bi2O3 33:67	(KNa)Cl	Small dia Au sealed	775 °C(18h)→645 °C @ 1 °C/h	CaBi2O4
50 wt%	50 wt%
CaO:1/2Bi2O3 1:2	(KNa)Cl	Large dia Ft sealed	750 °C→645 °C @ 1 °C/h 645 °C 64 h
20 wt%	80 wt%
CaO:1/2Bi2O3 1:2	(KNa)Cl	Large dia Pt	750 °C→645 °C @ 1 °C/h 645 °C 64 h
20 wt%	80 wt%
CaO:1/2Bi2O3 1:2	(KNa)Cl	vycor cruc.	675 °C 144 h
20 wt%	80 wt%
CaO:1/2Bi2O3 1:2	None	Small dia Au sealed	925 °C→850 °C @ 3 °C/h 850 °C 24 h quenched (liq N2 cooled He cup) crushed
		Small dia Au open	500 °C→700 °C @ 3 °C/h 700 °C 168 h
CaO:1/2Bi2O3 1:2	None	Small dia Au sealed	925 °C→850 °C @ 3 °C/h
		Small dia Au open	650 °C 16 h
CaO:1/2Bi2O3 1:2	(KNa)Cl	Large dia Au sealed	650 °C→750 °C @ 10 °C/h
80 wt%	20 wt%		750 °C→640 °C @ 1 °C/h
CaO:1/2Bi2O3 1:2	10μL H2O	Small dia Au sealed	Hydrothcrnal unit 700 °C 100 MPa
CaO:1/2Bi2O3 1:2	None	Large dia Au sealed	750 °C→875 °C @ 25 °C/h 875 °C→845 °C @ 1 °C/h
CaO:1/2Bi2O3 1:2	None	Small dia Au sealed	925 °C 10 min quenched (liq N2 cooled He cup) crushed to a fine powder
		Small dia Au open	500 °C→700 °C @ 3 °C/h
CaO:1/2Bi2O3 2:3	None	Small dia Au sealed	1000 °C→900 °C @ 1°C/h crushed
		Small dia Au sealed	825 °C 190 h furnace cooled
CaO:1/2Bi2O3 2:3	None	Small dia Au sealed	1000 °C 1 h quenched (liq N2 cooled He cup)	Ca4Bi6O13
			875 °C 260 h
CaO:1/2Bi2O3 2:3	(KNa)Cl	Large dia Au sealed	840 °C→640 °C @ 1 °C/h
98 wt%	2 wt%
CaO:1/2Bi2O3 2:3	(KNa)Cl	Large dia Au sealed	840 °C→640 °C @ 1 °C/h
80 wt%	20 wt%
CaO:1/2Bi2O3 2:3	(KNa)Cl	Large dia Au sealed	840 °C→640 °C @ 1 °C/h
50 wt%	50 wt%
CaO:1/2Bi2O3 2:3	(KNa)Cl	Large dia Au sealed	840 °C→640 °C @ 1 °C/h
20 w%	80 wt%
CaO:1/2Bi2O3 7:10	(KNa)Cl	Large dia Pt sealed	750 °C→645 °C @ 1 °C/h 645 °C 64 h	Ca4Bi6O13
20 wt%	80 wt%
CaO:1/2Bi2O3 7:10	(KNa)Cl	Large dia Pt	750 °C→645 °C @ 1 °C/h
20 wt%	80 wt%
CaO:1/2Bi2O3 6:7	CaCl2	Large dia Au open	900 °C 20 h
80 wt%	20 wt%
CaO:1/2Bi2O3 1:1	(KNa)Cl	Small dia Au sealed	650 °C→950 °C @ 100 °C/h 950 °C→900 °C @ 1 °C/h
80 wt%	20 wt%
CaO:1/2Bi2O3 1:1	(KNa)Cl	Small dia Au sealed	650 °C→950 °C @ 100 °C/h 950 °C→900 °C @ 1 °C/h
50 wt%	50 wt%
CaO:1/2Bi2O3 1:1	(KNa)Cl	Small dia Au sealed	650 °C→950 °C @ 100 °C/h 950 °C→900 °C @ 1 °C/h
20 wt%	80 wt%
CaO:1/2Bi2O3 7:6	(KNa)Cl	Large dia Pt sealed	750 °C→645 °C@ 1 °C/h 645 °C 64 h	Ca2Bi2O5
20 wt%	80 wt%
CaO:1/2Bi2O3 7:6	(KNa)Cl	Large dia Pt	750 °C→645 °C @ 1 °C/h
20 wt%	80 wt%
CaO:1/2Bi2O3 7:6	(KNa)Cl	Large dia Au sealed	900 °C 19.5 h
80 wt%	20 wt%

Equilibrium in this system has proven to be so difficult to obtain that a few specimens were prepared by utilizing lactic acid in an organic precursor route to obtain more intimate mixing at low temperatures [9]. This procedure yielded an essentially single phase amorphous precursor for the composition that contains 66.7 mol % Bi₂O₃. At higher Bi contents, pure Bi metal was formed by carbothermic reduction under even the lowest temperature drying procedures in air.

Specimens for solidus and liquidus determinations in the CaO-CuO system were prepared by dissolving mixtures of cupric nitrate and calcium nitrate in distilled water and then drying. The specimens were calcined two or three times between 500 and 700 °C with intermittent grinding. Samples of Ca_1−xCuO₂ were heated in a horizontal tube furnace for 36 to 120 h in air or in oxygen. In determining the exact stoichiometry of the compound previously reported as “CaCuO₂” [7], however, a citrate synthesis route was used [15]. Dried anhydrous calcium carbonate and basic cupric carbonate (Cu(OH)₂:CuCO₃) were dissolved in dilute nitric acid and complexed with excess citric acid monohydrate. After drying, the resulting friable, low-density material was calcined at 700 °C either in air or in a flowing oxygen atmosphere until x-ray diffraction revealed the presence of fewer than three phases. It took 18 to 84 h for these synthesis reactions to reach completion.

3. Experimental Results and Discussion

Most of the experiments performed on the binary and ternary mixtures of CaO-Bi₂O₃-CuO are reported in Table 1a. Additional experiments specifically designed in an attempt to obtain crystals large enough for x-ray single crystal studies are detailed in Table 1b. Crystallographic data for various phases are reported in Table 2.

Table 2.

Crystal structure data

Chemical formula	Symmetry phase (T °C)	a (Å)	b (Å)	c (Å)	α degrees	β degrees	γ degrees
Ca1−x,CuO2 x =0.172	Fmmma T ~700 °C	2.8047b (7)	6.321 (2)	10.573 (2)
CaO:1/2Bi2O3 1:6	$\mathrm{R}\overline{3}$ T ~750 °C	3.9448 (8)		27.8400 (8)
	Cmmm T ⩽735 °C	6.8188 (3)	3.9531 (2)	27.830 (1)
CaO:1/2Bi2O3 3:8	$\mathrm{R}\overline{3}$ α′ (T ~780 °C)	7.7427 (9)		9.465 (1)
	B2/m α″(T ~760 °C)	15.5819 (3)	3.8077 (1)	10.8955 (3)		91.829 (2)
Ca5Bi12O41	$\mathrm{P}\overline{1}$	9.934 (1)	15.034 (2)	15.008 (2)	82.65 (1)	85.27 (1)
CaBi2O4	C2/c	16.6295 (8)	11.5966 (5)	14.0055 (6)		134.036 (3)
Ca4Bi6O13	C2mm	17.3795 (5)	5.9419 (2)	7.2306 (2)
CaO:1/2Bi2O3 9:10	“bcc” T ~1000 °C	4.2458 (1)
Ca2Bi2O5	$\mathrm{P}\overline{1}$	10.1222 (7)	10.146 (6)	10.4833 (7)	116.912 (5)	107.135 (6)	92.939 (6)
Ca6+xSr6−xBi14O33 x→6	C-centered monoclinic	21.295 (4)	4.3863 (8)	12.671 (2)		102.74 (1)

^aIndicates a subcell.

^bNumbers in parentheses indicate uncertainties in final digits.

3.1 The System Bi₂O₃-CuO

A phase diagram for this system was already published [16], and was redrawn as Fig. 6392 in Phase Diagrams for Ceramists (PDFC) [17]. It apparently contains only one compound Bi₂CuO₄, (B₂Cu). No attempt was made to reinvestigate the melting relations of this system because it does not have any great effect on the phase equilibria of the ternary system with CaO.

3.2 The System CaO-CuO

Although a revised phase diagram for this system was previously reported [7], further experimental evidence (Table 1a) was accumulated in this study and the diagram was revised again [18] as shown in Fig. 1. The CaCu₂O₃ compound, which was reported to be stable only above 950 °C [19], was found to be stable between 985 and 1018 °C. Previously determined temperatures, 1020 and 1013 °C [20,7] for the decomposition of CaCu₂O₃(CCu₂) and for eutectic melting, respectively, are within experimental error of the new values, 1018 ± 2 °C and 1012 ± 2 °C.

Fig. 1.

CaO-CuO phase diagram.

3.2.1 Ca₂CuO₃

The Ca₂CuO₃(C₂Cu) compound decomposes into CaO plus liquid above 1034 ± 2 °C, which is slightly above the previous estimate of 1030 °C [20,7]. The composition of the eutectic reaction is 20CaO−80CuO±5%, as determined from the presence or absence of the Ca₂CuO₃ phase in samples of varying compositions that were quenched from 1020 °C.

3.2.2 Ca_1−xCuO₂

Samples prepared with an original Ca:Cu ratio of 45.33:54.67 contained no detectable CaO or CuO after heating in oxygen at 700 °C, as demonstrated by x-ray diffraction (Fig. 2 and Table 3). Compositions with original Ca:Cu ratios of 45.20:54.80 and 45.45:54.54 (≈5:6) yielded x-ray patterns which indicated the presence of excess CuO and excess CaO, respectively. Therefore, the Ca:Cu ratio for this compound is 0.453:0.547 or Ca_1−xCuO₂ with the composition Ca_0.828CuO₂ (x = 0.172) at 700 °C in oxygen. The single phase region for this phase probably varies with temperature and partial pressure of oxygen. The composition and structural analyses of this phase have been recently reported [15]. The x-ray powder diffraction pattern for Ca_1−xCuO₂ is shown in Fig. 2 and the indexed data is given in Table 3. This compound decomposes into Ca₂CuO₃ plus CuO above 755 °C in air and 835 °C in oxygen. In Fig. 1, the experiments conducted in air and those conducted in an oxygen atmosphere are indicated by the dashed line and the crosses, respectively. At 675 °C, Ca_1−xCuO₂ can be synthesized from CaCO₃ plus CuO but the run product never fully equilibrates to a single- or two-phase assemblage. Rather, the metastable three-phase assemblage Ca_1−xCuO₂+CaO+CuO persists: after five cycles of heating with intermittent grinding the relative proportions of phases were Ca_1−xxCuO₂>CaO> CuO and they remained that way for an additional overnight heat treatments. Because of its greattional 31 overnight heat treatments. Because of its great persistence, Ca_1−xCuO₂ is interpreted as being an equilibrium phase, but it should be noted that reversal of its decomposition (synthesis from CuO+Ca₂CuO₃) was not successfully demonstrated.

Fig. 2.

Ca_1−xCuO₂ x-ray diffraction powder pattern (CaO:CuO 45.328:54.672).

Table 3.

x-ray powder diffraction data for the compound Ca_1−xCuO₂

d obs(Å)	Rel I (%)	2θ obs	2θ calca	hkl
5.273	13	16.80	16.76	002
3.1554	21	28.26	28.21	002
3.0994	1	28.78b
2.8914	6	30.90	30.91	1−8δ,1,1−δc
2.8245	3	31.65	31.66	1−8δ,1,1+δc
2.7106	100	33.02	32.99	022
2.6407	22	33.92	33.89	004
2.4887	23	36.06	36.02	111
2.3218	6	38.75	38.77	1−δa,1,3−δc
2.2207	7	40.59	40.60	1−δa,1,3+δc
2.0720	61	43.65	43.62	113
1.7666	4	51.70	51.72	1−δa,3,1−δc
1.7613	6	51.87	51.84	600
1.7571	6	52.00	51.95	1−δa,1,5−δc
1.7527	8	52.14	52.21	1−δa,3,1+δc
1.6840	2	54.44	54.39	1−δa,1,5+δc
1.6632	10	55.18	55.16	131
1.6306	29	56.38	56.36	115
1.6088	2	57.21	57.23	1−δa,3,3−δc
1.5802	12	58.35	58.34	040
1.5397	18	60.04	60.06	026
1.5200	16	60.90	60.90	133
1.4811	1	62.67b
1.4545	1	63.95b
1.4467	1	64.34b
1.4129	1	66.07b
1.4025	6	66.63	66.64	200
1.3702	1	68.41	68.42	1−δa,1,7−δc
1.3565	12	69.20	69.21	044
1.3471	2	69.75b
1.3208	13	71.35	71.33	1−δa,1,7+δc
1.3186	15	71.49	71.55	135
1.3018	5	72.56	72.59	117
1.2819	5	73.87	73.87	220

^aCalculated on the basis of an orthorhombic subcell, Fmmm, a =2.8047 (7), b =6.321 (2), and c = 10.573 (2) Å.

^bSuperstructure probably not accounted for by δ-vectors.

3.2.3 Cu₂O in the Binary System

Cu₂O, which is known to be stable in air only above 1026 °C, was found in this system above 1012 °C. Therefore, Cu⁺ and Cu²⁺ must have coexisted in the samples that were quenched in air from temperatures between 1012 and 1026 °C. The Cu₂O observed in samples that were quenched from below 1026 °C is probably formed during solidification of the liquid phase; i.e., an oxygen deficiency in the liquid may result in the solidification of Cu₂O as well as CuO.

3.3 The System CaO-Bi₂O₃

The phase equilibria diagram for the system CaO-Bi₂O₃ was reported in [21] and redrawn as Fig. 6380 in PDFC [17]. It is reproduced here as Fig. 3 with the scale changed to l/2Bi₂O₃-CaO instead of Bi₂O₃-CaO, to maintain consistency with the other phase diagrams in this report. An interpretation of the experimental results recorded in Table 1 was published in [19] and it is shown in Fig. 4 (cf. Fig. 3). The major differences between our new diagram and the one presented in [21] are: 1) the composition of “Ca₇Bi₁₀O₂₂” [21,22] is revised to Ca₄Bi₆O₁₃ (2:3) and its crystal structure is reported in [23]; 2) the composition of “Ca₇Bi₆O₁₆” [21,22] is now reported as Ca₂Bi₂O₅, and its crystal structure is given in [24]; 3) a metastable phase ~Ca₆Bi₇O_16.5 was formed at about 925 °C on the CaO-rich side of Ca₂Bi₂O₅, but at about 885 °C on the CaO-poor side; 4) melting relations have been determined in the region of 20–50 mol % CaO.

Fig. 3.

CaO-1/2Bi₂O₃ phase diagram as changed from PDFC 6380-Conflant et al.

Fig. 4.

CaO-1/2Bi₂O₃—present phase diagram.

3.3.1. Rhombohedral Solid Solution (Sillen Phase-Rhomb)

The rhombohedral solid solution was first reported by Sillen [25]. Phase relations in the CaO-rich region of the Sillen phase field were previously [20] represented as exhibiting a congruent transition to the fcc solid solution, and the present experiments indicate such a point at (~22 mol % CaO, ~835 °C). Conflant et al. [21] reported a phase transition from one rhombohedral phase to another at about 735–740 °C. Differential thermal analysis of a 1:6 ratio CaO:1/2Bi₂O₃ specimen confirms the presence of a reversible transition at about 735 °C. Samples quenched from ~750 °C are clearly rhombohedral as previously reported [21,22], but x-ray patterns (Figs. 5a, 5b; Tables 4, 5, 6) from samples that were quenched from ⩽735 °C exhibit peak splitting and faint superstructure reflections (Fig. 5b). The diffraction patterns for both the high and low temperature forms are much sharper if the specimens are not ground after quenching. Apparently, it is easy to induce mechanical deformation in these samples by grinding. The peak splitting can be indexed with an orthorhombic cell a =6.8188(3), b =3.9531(2), and c =27.830(1) Å, which is most easily observed in the rhombohedral (0,2,13) and (3,0,9) reflections corresponding to (2,2,13)+ (4,0,13) and (3,3,9)+ (6,0,9), respectively, in the orthorhombic indexing (Figs. 5a, 5b, and Tables 5, 6). Dimensionally the unit cell is orthorhombic, but the symmetry cannot be higher than monoclinic because it is the derivative of a rhombohedral (rather than hexagonal) high symmetry phase. Single crystals prepared at 700 °C with a salt eutectic flux (Table 1b) give a biaxial interference figure, in polarized light, parallel to the pseudo-rhombohedral c axis.

Fig. 5a.

x-ray powder diffraction pattern CaO:1/2Bi₂O₃ 1:6 quenched from 740 °C.

Fig. 5b.

x-ray powder diffraction pattern of CaO:1/2Bi₂O₃ 1:6 quenched from 740 °C (rhombohedral indexing) and 725 °C (orthorhombic indexing).

Table 4.

x-ray powder diffraction data for the high temperature rhombohedral (Sillen phase) indexing of CaO:1/2Bi₂O₃ 1:6

d obs(Å)	Rel I(%)	2 θ obs	2 θ calca	hkl
9.254	4	9.55	9.52	003
4.633	8	19.14	19.11	006
3.3897	23	26.27	26.26	101
3.3166	31	26.86	26.85	012
3.0922	93	28.85	28.84	009
3.0651	100	29.11	29.09	104
2.9099	56	30.70	30.68	015
2.5896	16	34.61	34.58	107
2.4372	17	36.85	36.84	018
	2	39.90b
2.1578	10	41.83	41.82	1,0,10
	2	43.67b
2.0326	17	44.54	44.52	0,1,11
1.9726	57	45.97	45.98	110
1.9283	1	47.09	47.07	113
1.8554	12	49.06	49.04	0,0,15
1.8149	57	50.23	50.22	116
			50.24	1,0,13
1.7188	24	53.25	53.26	0,1,14
1.7043	8	53.74	53.72	021
1.6953	10	54.05	54.05	202
1.6629	72	55.19	55.19	119
1.6333	16	56.28	56.29	205
1.5694	6	58.79	58.79	027
1.5500	10	59.60	59.58	1,0,16
1.5467	18	59.74	59.74	0,0,18
1.5334	6	60.31	60.31	208
1.4770	12	62.87	62.88	0,1,17
1.4561	2	63.88	63.89	0,2,10
1.4157	6	65.93	65.92	2,0,11
1.3516	7	69.49	69.49	1,1,15
1.3355	12	70.45	70.46	0,2,13
1.2956	8	72.96	72.95	2,0,14
1.2891	10	73.39	73.39	0,1,20
1.2856	11	73.62	73.61	122
1.2693	15	74.73	74.71	214
1.2579	13	75.52	75.53	125
1.2280	4	77.70	77.69	217
1.2171	21	78.53	78.53	1,1,18
1.2105	5	79.04	79.03	128
1.1868	14	80.94	80.95	1,0,22
1.1823	9	81.31	81.33	2,0,17
1.1712	2	82.25	82.24	2,1,10
1.1598	3	83.24	83.22	0,0,24
1.1503	5	84.08	84.09	1,2,11
1.1407	8	84.95	84.93	0,1,23
1.1386	12	85.15	85.13	300
1.1122	1	87.67	87.68	0,2,19
1.1059	13	88.30	88.30	306
			88.31	2,1,13
1.0828	7	90.70	90.68	1,2,14
1.0790	2	91.11	91.10	2,0,20
1.0686	10	92.25	92.24	309
1.0587	2	93.37	93.36	1,0,25
1.0368	2	95.97	95.95	2,1,16
1.0309	7	96.70	96.67	0,0,27
1.0217	8	97.86	97.86	0,1,26
1.0169	8	98.49	98.50	0,2,22
1.0141	9	98.86	98.87	1,2,17
0.9999	3	100.77	100.78	1,1,24
0.9876	3	102.52	102.52	2,0,23
0.9863	4	102.70	102.72	220
0.9707	1	105.04	105.05	3,0,15
0.9469	4	108.88	108.87	131
0.9454	4	109.14	109.15	312
0.9394	8	110.16	110.13	229
0.9341	4	111.10	111.11	315
0.9330	3	111.31	111.33	0,2,25
0.9243	2	112.90	112.91	0,1,29
0.9218	3	113.36	113.38	137
0.9171	7	114.27	114.28	3,0,18
0.9141	10	114.84	114.83	318
0.9076	3	116.14	116.15	2,2,12
0.9072	3	116.22	116.22	2,0,26
0.9038	7	116.92	116.93	2,1,22
0.8970	1	118.35	118.36	1,3,10
0.8875	2	120.45	120.47	3,1,11
0.8832	3	121.43	121.45	1,2,23
0.8686	6	124.95	124.97	1,0,31
0.8665	7	125.50	125.49	1,3,13
0.8554	4	128.46	128.46	3,1,14

^aCalculated on the basis of a rhombohedral unit cell, $\mathrm{R}\overline{3}$, a =3.9448(8) and c =27.8400(8) Å.

^bApparently due to an unidentified structure.

Table 5.

x-ray powder diffraction data for the low temperature orthorhombic indexing of CaO:1/2Bi₂O3 1:6

d obs(Å)	Rel I(%)	2 θ obs	2 θ calca	hkl
9.283	1	9.52	9.53	003
4.6405	10	19.11	19.12	006
	1	25.15b
3.3922	17	26.25	26.23	111
3.3190	24	26.84	26.82	112
3.0911	100	28.86	28.85	009
3.0703	84	29.06	29.07	114
2.9127	47	30.67	30.66	115
2.5911	14	34.59	34.57	117
2.4391	13	36.82	36.82	118
2.4359	14	36.87	36.88	208
	1	38.29b
	1	38.90b
	1	40.76b
2.1588	7	41.81	41.81	1,1,10
2.1563	7	41.86	41.87	2,0,10
	1	43.01b
2.0339	15	44.51	44.51	1,1,11
2.0326	1	44.54	44.56	2,0,11
1.9775	25	45.85	45.87	020
1.9726	40	45.97	46.00	021
	1	47.17b
	1	48.20b
1.8550	5	49.07	49.06	0,0,15
1.8152	51	50.22	50.24	1,1,13
1.8142	49	50.25	50.27	316
	1	51.92b
	1	52.07b
	2	52.90b
1.7188	22	53.25	53.26	1,1,14
1.7174	15	53.30	53.30	2,0,14
1.7070	6	53.65	53.66	221
1.7011	5	53.85	53.84	401
1.6976	6	53.97	53.98	222
1.6924	5	54.15	54.16	402
1.6660	34	55.08	55.10	029
1.6618	54	55.23	55.23	319
1.6607	47	55.27	55.28	224
1.6563	28	55.43	55.45	404
1.6343	10	56.24	56.23	225
1.6298	9	56.41	56.41	405
	1	56.98b
	2	58.34b
1.5704	4	58.75	58.73	227
1.5662	4	58.92	58.90	407
1.5464	18	59.75	59.76	0,0,18
1.5348	5	60.25	60.26	2,2,18
1.5309	3	60.42	60.43	408
	1	61.15b
1.4764	10	62.90	62.89	1,1,17
1.4753	9	62.95	62.93	2,0,17
1.4567	1	63.85	63.84	2,2,10
	2	63.90b
1.4532	1	64.02	64.00	4,0,10
1.4164	3	65.89	65.87	2,2,11
1.4139	3	66.02	66.03	4,0,11
1.3526	4	69.43	69.42	0,2,15
1.3506	4	69.55	69.54	3,1,15
1.3362	9	70.41	70.41	2,2,13
1.3335	10	70.57	70.57	4,0,13
	1	71.22b
1.2964	6	72.91	72.91	2,2,14
1.2942	6	73.05	73.06	4,0,14
1.2889	9	73.40	73.40	1,1,20
1.2852	7	73.65	73.64	422
1.2719	6	74.55	74.54	134
1.2694	8	74.72	74.73	424
1.2678	9	74.83	74.84	514
1.2603	6	75.35	75.36	135
1.2575	7	75.55	75.55	425
1.2562	7	75.64	75.66	515
	2	77.45b
1.2263	3	77.83	77.83	517
1.2167	17	78.56	78.58	3,1,18
1.1866	13	80.96	80.97	1,1,22
1.1862	12	80.99	81.01	2,0,22
1.1734	2	82.06	82.08	1,3,10
1.1699	1	82.36	82.37	5,1,10
1.1594	2	83.27	83.25	0,0,24
1.1496	3	84.14	84.12	4,2,11
1.1409	6	84.93	84.95	1,1,23
1.1404	7	84.98	84.99	2,0,23
1.1399	7	85.03	85.02	330
1.1364	5	85.35	85.35	600
	2	85.60b
1.1266	1	86.27	86.25	5,1,12
	1	87.50b
1.1075	4	88.14	88.16	1,3,13
1.1070	5	88.19	88.18	336
1.1054	6	88.35	88.34	4,2,13
1.1045	7	88.44	88.45	5,1,13
1.1039	6	88.50	88.51	606
1.0842	3	90.55	90.53	1,3,14
1.0827	4	90.71	90.71	4,2,14
1.0818	4	90.80	90.82	5,1,14
1.0793	3	91.07	91.07	2,2,20
1.0780	3	91.22	91.22	4,0,20
1.0694	5	92.16	92.14	339
1.0666	6	92.47	92.46	609
1.0586	2	93.38	93.39	1,1,25
1.0356	2	96.11	96.10	5,1,16
1.0306	5	96.74	96.72	0,0,27
1.0216	5	97.88	97.89	1,1,26
1.0170	6	98.48	98.48	2,2,22
1.0157	6	98.65	98.62	4,0,22

^aCalculated on the basis of an orthorhombic unit cell, Cmmm, a = 6.8188(3), b =3.9531(2), and c =27.830(1) Å.

^bApparently due to an unidentified structure.

Table 6.

x-ray powder diffraction data for the high temperature rhombohcdral (Sillen phase) indexing versus the orthorhombic indexing of CaO:1/2Bi₂O₃ 1:6

2 θ obs	Rhombohedral		Orthorhombic
	hkla	hklb	2 θ obs
9.55	003	003	9.52
19.14	006	006	19.11
			25.15b
26.27	101	111	26.25
26.86	012	112	26.84
28.85	009	009	28.86
29.11	104	114	29.06
30.70	015	115	30.67
34.61	107	117	34.59
36.85	018	118	36.82
		208	36.87
			38.29b
			38.90b
39.90b
			40.76b
41.83	1,0,10	1,1,10	41.81
		2,0,10	41.86
			43.01b
43.67b
44.54	0,1,11	1,1,11	44.51
		2,0,11	44.54
		020	45.85
45.97	110	021	45.97
47.09	113
			47.17b
			48.20b
49.06	0,0,15	0,0,15	49.07
50.23	116	1,1,13	50.22
	1,0,13
		316	50.25
			51.92b
			52.07b
			52.90b
53.25	0,1,14	1,1,14	53.25
		2,0,14	53.30
		221	53.65
53.74	021
		401	53.85
		222	53.97
54.05	202
		402	54.15
		029	55.08
55.19	119	319	55.23
		224	55.27
		404	55.43
56.28	205	225	56.24
		405	56.41
			56.98b
			58.34b
58.79	027	227	58.75
		407	58.92
59.60	1,0,16
59.74	0,0,18	0,0,18	59.75
		2,2,18	60.25
60.31	208
		408	60.42
			61.15b
62.87	0,1,17	1,1,17	62.90
		2,0,17	62.95
63.88	0,2,10	2,2,10	63.85
			63.90b
		4,0,10	64.02
65.93	2,0,11	2,2,11	65.89
		4,0,11	66.02
		0,2,15	69.43
69.49		1,1,15
		3,1,15	69.55
70.45	0,2,13	2,2,13	70.41
		4,0,13	70.57
			71.22b
72.96	2,0,14	2,2,14	72.91
		4,0,14	73.05
73.39	0,1,20	1,1,10	73.40
73.62	112	422	73.65
		134	74.55
74.73	214	424	74.72
		514	74.83
		135	75.35
75.52	125	425	75.55
		515	75.64
			77.45b
77.70	217
		517	77.83
78.53	1,1,18	3,1,18	78.56
79.04	128
80.94	1,0,22	1,1,22	80.96
		2,0,22	80.99
81.31	2,0,17
		1,3,10	82.06
82.25	2,1,10
		5,1,10	82.36
83.24	0,0,24	0,0,24	83.27
84.08	1,2,11
		4,2,11	84.14
84.95	0,1,23	1,1,23	84.93
		330	85.03
85.15	300
		600	85.35
			85.60b
		5,1,12	86.27
			87.50b
87.67	0,2,19
		1,3,13	88.14
		336	88.19
88.30	306
	2,1,13
		4,2,13	88.35
		5,1,13	88.44
		606	88.50
		1,3,14	90.55
90.70	1,2,14
		4,2,14	90.71
		5,1,14	90.80
91.11	2,0,20	2,2,20	91.07
		4,0,20	91.22
92.25	309	339	92.16
		609	92.47
93.37	1,0,25	1,1,25	93.38
95.97	2,1,16
		5,1,16	96.11
96.70	0,0,27	0,0,27	96.74
97.86	0,1,26	1,1,26	97.88
98.49	0,2,22	2,2,22	98.48
		4,0,22	98.65
98.86	1,2,17

^aCalculated on the basis of a rhombohedral unit cell, $\mathrm{R}\overline{3}$, a =3.9448(8) and c =27.8400(8) Å.

^bCalculated on the basis of an orthorhombic unit cell, Cmmm, a =6.8188(3), b =3.9531(2), and c =27.830(1) Å.

^cApparently due to an unidentified superstructure.

3.3.2. “Face-Centered-Cubic” Solid Solution (“fcc”)

Levin and Roth [26] demonstrated that the solidus temperature of fcc Bi₂O₃ (α₁ in [21]) increases with additions of CaO. Conflant et al. [21] depicted its homogeneity range as extending to temperatures above the rhombohedral Sillen phase, and they did not include a congruent melting point. The present work and [18], however, indicate that there is a congruent melting point between 20 and 23 mol % CaO at about 885 °C. The phase diagram in [21] includes a dashed line which defines a small α₁′ region in the CaO-rich, low temperature portion of the fcc field. Present results are essentially in agreement with this finding; i.e., all x-ray diffraction patterns from quenched “fcc” samples that contain at least 20 mol % CaO exhibit the superstructure peaks described in [21] plus a very slight splitting of cubic diffraction maxima that was not described in [21] (Fig. 6, Table 7). The observed splitting of substructure peaks of α₁′ fits rhombohedral symmetry with a_H=7.7427(9), c_H = 9.465(1) Å, c/a = 1.2224. The complete field, extending to about 30 mol % CaO, is labeled “fcc” because neither the data presented here nor that in [20] provides a sound basis for drawing definitive phase boundaries. The minimum shown in Fig. 4 at ~773 °C for the CaO-rich end of this solid solution is in relatively good agreement with the value of 785 °C which can be interpreted from [21] (Fig. 3). When a single-phase specimen of composition near this minimum (5:14-3:8, CaO:1/2Bi₂O₃) is quenched after 10 min annealing at ~760 °C (~13 °C below the equilibrium minimum), the rhombohedral splitting of cubic maxima was greatly enhanced; this is the α₁″ phase of [21] (Fig. 6; Table 8). As with the rhombohedral Sillen-type phases, these rhombohedrally distorted fcc phases are highly susceptible to mechanical damage during routine grinding, therefore the line splitting of α₁’ can only be seen if the quenched specimen is not ground. X-ray analysis of this sample yielded a_H = 7.616, c_H = 9.6477, c/a =1.2668, whereas hexagonal indexing of a truly cubic pattern would give c/a= 1.2247; [1,1,1]_c=[0,0,0,3]_H and ${[2,2,0]}_{\mathrm{c}}={[2,2,4\overline{4},0]}_{\mathrm{H}}$. Thus, the rhombohedrally distorted phase that was quenched from the stable “fcc” region (α₁′) had a c/a ratio that was slightly smaller than the cubic value, but the metastable lower-temperature phase (α₁″) that was quenched from below the “fcc” region had a c/a ratio that was considerably larger than the cubic value. Single crystal x-ray precession patterns from the α₁″ phase (Fig. 7) can be indexed with either a monoclinic or a rhombohedral cell with a =4a_sub as shown in Table 8.

Fig. 6.

x-ray powder diffraction pattern of the fcc phase showing splitting and superstructure of α₁′ and α₁″.

Table 7.

x-ray powder diffraction data for the α₁′ phase (CaO:1/2Bi₂O₃ mol ratio 3:8, 780 °C quench, sample not ground)

d obs(Å)	Rel I (%)	2 θ obs	2 θ calca	hkl
8.990	2	9.83
4.669	4	18.99
3.5296	7	25.21
3.5050	6	25.39
3.1565	100	28.25	28.26	003
2.9946	2	29.81
2.9492	1	30.28
2.7339	58	32.73	32.71	202
2.3510	4	38.25
2.0031	5	45.23
1.9517	3	46.49
1.9341	54	46.94	46.96	024
1.8882	2	48.15
1.8801	5	48.37
1.7875	1	51.05
1.7752	2	51.43
1.6940	1	54.09
1.6492	51	55.69	55.72	205
1.6184	1	56.84
1.5799	5	58.36	58.35	042
1.5770	5	58.48	58.46	006
1.5666	1	58.90
1.5482	2	59.67
1.4401	1	64.67
1.3906	2	67.27
1.3680	6	68.54	68.55	404
1.3515	1	69.49
1.3078	2	72.17
1.2762	1	74.25
1.2581	1	75.50
1.2558	8	75.67	75.66	241
1.2537	8	75.82	75.80	027
1.2231	8	78.07	78.09	226
1.2089	1	79.16
1.1828	1	81.27
1.1796	1	81.53
1.1528	1	83.85
1.1174	5	87.16	87.15	600
1.1155	4	87.35	87.33	208
1.0533	5	94.00	94.03	425
1.0245	7	97.50
1.0077	7	99.70

^aCalculated on the basis of a rhombohedral unit cell, $\mathrm{R}\overline{3}$, a =7.7427(9) and c =9.465(1) Å.

Table 8.

x-ray powder diffraction data for the α₁″ phase (CaO:1/2Bi₂O₃ mol ratio 3:8, 760 °C quench, not ground)

d obs (Å)	Rel I (%)	2 θ obs	2 θ calca	hkla	2 θ calcb	hklb
8.812	<2	10.03	10.05	300	10.05	101
4.631	1	19.15	19.16	051	19.16	301
	<1	21.41	2:3		2:3
3.5618	15	24.98	24.99	502	24.99	$10\overline{3}$
3.5120	11	25.34	25.35	701	25.35	$11\overline{1}$
3.2156	27	27.72	27.72	003	27.72	$40\overline{2}$
3.1208	100	28.58	28.58	081	28.58	$40\overline{2}$
	2	29.38	2:3		2:3
3.0225	7	29.53	29.55	303	29.55	$30\overline{3}$
	1	30.80c
	<1	31.09c
	1	32.27c
2.7226	55	32.87	32.87	802	32.87	004
	<1	34.39c
	<1	34.57c
2.5817	<1	34.72	34.73	381	34.73	113
2.3417	4	38.41	38.41	832	38.41	511
2.3265	3	38.67	38.65	0,11,1	38.66	503
2.3231	3	38.73	38.73	850	38.74	313
2.1934	2	41.12	41.12	054	41.12	701
2.1707	<1	41.57	41.56	244	d
2.1485	1	42.02	42.00	514	42.04	105
2.0322	8	44.55	44.57	704	44.56	$51\overline{3}$
1.9866	4	45.63	45.64	13,0,1	45.65	305
1.9466	28	46.62	46.62	084	46.62	800
1.9039	34	47.73	47.73	880	47.73	020
8.812	<2	10.03	10.05	300	10.05	101
4.631	1	19.15	19.16	051	19.16	301
	<1	21.41	2:3		2:3
1.9866	4	45.63	45.64	13,0,1	45.65	305
1.9466	28	46.62	46.62	084	46.62	800
1.9039	34	47.73	47.73	800	47.73	020
1.8828	9	48.30	48.29	853	48.30	115
					48.30	711
1.8382	<1	49.55	49.54	235	d
1.8125	4	50.30	50.31	505	51.31	505
1.7929	3	50.89	50.90	384	50.90	$31\overline{5}$
1.7613	<1	51.87	51.88	13,3,1	51.89	315
					51.89	$32\overline{1}$
1.7176	4	53.29	53.29	075	53.29	713
1.7008	1	53.86	53.86	0,11,4	53.87	901
1.6786	4	54.63	54.62	3,13,2	54.62	$12\overline{3}$
1.6652	12	55.11	55.10	805	55.10	$40\overline{6}$
1.6384	34	56.09	56.09	883	56.09	422
1.6253	20	56.58	56.58	16,0,1	56.58	406
1.6102	4	57.16	57.14	11,5,3	57.14	$32\overline{3}$
					57.15	$52\overline{1}$
1.6079	4	57.25	57.25	006	57.25	$80\overline{4}$
1.5821	4	58.27	58.29	306	58.28	$70\overline{5}$
					58.29	$90\overline{3}$
1.5650	4	58.97	58.94	835	58.95	$91\overline{1}$
1.5602	13	59.17	59.17	0,16,2	59.17	024
					59.17	804
1.5526	4	59.49	59.48	13,0,4	59.48	$10\overline{7}$
1.5490	2	59.64	59.63	295	d
1.5033	1	61.65	61.64	11,0,5	61.64	$30\overline{7}$
	<1	62.58c		*
1.4738	<1	63.02	63.03	16,3,1	63.03	523
1.4382	1	64.77	64.78	13,3,4	64.78	$11\overline{7}$
					64.79	$72\overline{1}$
1.4303	1	65.17	65.18	16,1,3	65.18	913
1.4218	1	65.61	65.63	8,13,1	65.63	715
1.3773	3	68.01	68.01	13,8,2	68.01	317
1.3743	3	68.18	68.18	19,0,1	68.18	325
1.3614	6	68.92	68.93	16,0,4	68.93	008
					68.93	820
1.3338	1	70.55	70.56	18,0,3	70.57	$11,0,\overline{3}$
1.3221	4	71.27	71.27	856	71.27	$51\overline{7}$
					71.27	$11,1,\overline{1}$
1.3127	2	71.86	71.86	3,13,5	71.86	$52\overline{5}$
1.2942	2	73.05	73.04	707	73.03	$70\overline{7}$
					73.04	915
1.2717	2	74.56	74.55	11,11,3	74.56	$12,0,\overline{2}$
			74.57	087	74.57	$81\overline{6}$
1.2687	2	74.77	74.79	16,3,4	74.80	921
1.2536	4	75.83	75.83	0,16,5	75.84	12,0,2
1.2360	11	77.10	77.09	8,16,1	77.09	426
1.2285	4	77.66	77.66	886	77.66	$82\overline{4}$
1.2256	4	77.88	77.89	387	77.88	$71\overline{7}$
1.2168	3	78.55	78.56	11,5,6	78.56	$92\overline{3}$
1.2065	8	79.35	79.33	16,8,2	79.34	824
1.2011	2	79.78	79.78	10,15,1	79.79	$10,0,\overline{6}$
			79.79	208
1.1798	1	81.52	81.51	3,16,5	81.51	$32\overline{7}$
1.1703	1	82.33	82.34	21,0,3	82.34	309
1.1526	2	83.87	83.88	13,8,5	83.87	$11\overline{9}$
1.1489	2	84.21	84.23	078	84.23	$11,1,\overline{5}$
1.1402	1	85.00	84.99	18,6,3	85.00	$23\overline{4}$
			85.00	13,0,7	85.00	$50\overline{9}$
					85.00	630
					85.00	$13,1,\overline{1}$
1.1331	2	85.66	85.67	16,1,6	85.66	$31\overline{9}$
					85.67	$52\overline{7}$
1.1272	1	86.22	86.23	0,19,5	86.24	11,2,1
					86.24	13,0,3
1.1226	1	86.66	86.69	11,13,4	86.69	$53\overline{3}$
1.1074	5	88.15	88.16	8,16,4	88.16	028
					88.16	$43\overline{4}$
					88.16	12,1,4
1.0990	4	88.96	88.97	24,0,0	88.98	808
1.0922	2	89.70	89.69	16,10,3	88.69	228
			89.70	13,3,7	89.69	$51\overline{9}$
					89.69	10,2,4
					89.70	11,2,3
1.0768	1	91.35	91.38	5,19,4	91.38	$33\overline{5}$
1.0641	1	92.75	92.76	309	92.75	$11,0,\overline{7}$
					92.75	$13,0,\overline{5}$
1.0575	1	93.51	93.51	16,0,7	93.50	$4,0,1\overline{0}$
					93.51	12,2,2
1.0468	3	94.76	94.74	16,8,5	94.74	832
					94.74	12,2,2
1.0402	4	95.55	95.56	24,0,3	95.56	4,0,10
			95.57	7,12,7	95.56	12,0,6
1.0343	1	96.28	96.27	2,12,8	d
1.0212	<1	97.93	97.93	4,15,7	d
1.0203	<1	98.05	98.06	639	d
1.0115	1	99.20	99.22	21,8,1	99.22	719
1.0002	1	100.73	100.72	3,13,8	100.72	$15,1,\overline{1}$
0.9968	1	101.21	101.19	16,13,3	101.19	329
					101.20	11,2,5
0.9946	1	101.52	101.50	8,13,7	101.50	15,1,1
0.9898	1	102.20	102.20	26,1,1	102.18	15,0,3
0.9781	1	103.92	103.90	19,0,7	103.90	$52\overline{9}$
0.9733	2	104.64	104.64	859	104.64	$15,1,\overline{3}$
0.9622	1	106.37	106.37	0,2,10	106.36	$14,0,\overline{6}$
0.9520	2	108.03	108.02	16,16,0	108.03	828
					108.04	040
0.9432	1	109.51	109.52	5,25,1	109.54	16,1,0
0.9371	1	110.57	110.58	21,8,4	110.58	3,1,11
0.9332	1	111.26	111.27	26,2,3	111.29	$93\overline{5}$
0.9289	1	112.05	112.05	11,5,9	112.05	$11,2,\overline{7}$
0.9258	1	112.61	112.60	0,25,5	112.62	15,0,5
0.9242	1	112.91	112.91	2,7,10	112.92	2,3,
			112.92	2,24,5
0.9127	2	115.13	115.11	3,20,7	115.11	12,2,6
0.9104	5	115.58	115.56	0,19,8	115.57	15,2,1
					115.57	17,0,1
0.9074	3	116.19	116.17	24,0,6	116.18	12,3,0
			116.21	9,13,8	116.18	16,0,4
0.8984	2	118.05	118.06	20,4,7	118.07	$12,3,\overline{2}$
0.8939	1	119.02	119.00	29,0,2	119.01	7,0,11
0.8780	1	122.64	122.66	29,2,0	d
0.8755	1	123.25	123.23	5,24,5	123.23	1,2,11
					124.24	139
0.8738	1	123.66	123.66	13,11,8	123.66	$11,3,\overline{5}$
0.8732	1	123.80	123.81	21,13,2	123.79	139
					123.80	$74\overline{1}$
0.8710	1	124.35	124.37	5,18,8	d
0.8665	1	125.49	125.49	27,6,0	d

^aCalculated on the basis of a rhombohedral unit cell, $\mathrm{R}\overline{3}$, a =30.4640(5) and c =9.6477(2) Å.

^bCalculated on the basis of a monoclinic unit cell, B2/m, a = 15.5819(3), b = 3.8077(1), c = 10.8955(3) Å, and β =91.829(2)°.

^cApparently due to an unidentified superstructure.

^dNot indexable by the monoclinic all.

Fig. 7.

x-ray precession photograph of the fcc α₁″ phase (Mo radiation).

3.3.3. The “Body-Centered-Cubic” Solid Solution (“bcc”)

The phase referred to as body-centered-cubic (“bcc”) solid solution was reported as a high temperature phase in [21]. In the present study this phase was found to extend from about 35 to 45 mol % CaO. The exact boundaries of the two-phase “fcc-bcc” region were not determined because the compositions of coexisting phases were not consistently reproduced. Just as with the “fcc” phase the “bcc” phase also exhibits line splitting and superstructure. Distortions from cubic symmetry (Fig. 8, Table 9), seem to be greatest in samples that are quenched from the region near the decomposition point of the 2:3 phase, (Fig. 9, Table 10). Single crystal x-ray diffraction precession data (Fig. 10) confirm the distortion recorded in Fig. 9 and Table 10 and indicate the nature of the superstructure. CaO-rich phase boundaries of the “bcc” field have not been precisely determined in part because of complications arising from the presence in many experiments of a metastable phase (see “C-mon” below). This bcc-type phase was found to be stable down to a minimum temperature of 825 ± 5 °C (Fig. 4) which is in good agreement with the value of 819 °C interpreted from [20] (see Fig. 3).

Fig. 8.

x-ray powder diffraction pattern for the bcc phase.

Table 9.

x-ray powder diffraction data for the body centered cubic phase (CaO:1/2Bi₂O₃ mol ratio 9:10, 1000 °C quench)

d obs (Å)	Rel I (%)	2 θ obs	2 θ calca	hkl
3.0006	100	29.75	29.73	110
2.1239	34	42.53	42.52	200
1.7330	51	52.78	52.77	211
1.5011	14	61.75	61.75	220
1.3430	12	70.00	70.02	310
1.2255	3	77.89	77.88	222
1.1346	10	85.52	85.51	321
1.0617	1	93.03	93.06	400
1.0008	3	100.65	100.66	330
0.9494	2	108.45	108.46	420
0.9052	1	116.64	116.63	332
0.8667	1	125.43	125.45	422
0.8326	2	135.39	135.37	510

^aCalculated on the basis of a body centered cubic cell with a = 4.2458(1) Å.

Fig. 9.

x-ray powder diffraction pattern for the distorted bcc phase with line splitting and superstructure (CaO:1/2Bi₂O₃ 2:3 860 °C).

Table 10.

x-ray powder diffraction data for the distorted body centered cubic phase with line splitting and superstructure (CaO:1/2Bi₂O₃ mol ratio 2:3, 860 °C)

d obs (Å)	Rel I (%)	2 θ obs	2 θ calca	hkl
8.699	1	10.16
7.950	1	11.12
7.783	1	11.36
4.828	3	18.36
4.635	1	19.13
4.460	1	19.89
4.2267	2	21.00
4.1698	1	21.29
4.0826	1	21.75
3.9849	1	22.29
3.8868	1	22.86
3.5379	1	25.15
3.4714	3	25.64
3.3997	2	26.19
3.3164	1	26.86
3.2291	1	27.60
3.1410	1	28.39
3.0972	3	28.80
3.0015	100	29.74	29.73	110
2.8841	4	30.98
2.8245	2	31.65
2.7801	1	32.17
2.7526	1	32.50
2.7184	1	32.92
2.5924	1	34.57
2.5467	1	35.21
2.5300	1	35.45
2.4859	1	36.10
2.4609	1	36.48
2.4143	1	37.21
2.3901	1	37.60
2.3218	1	38.75
2.3012	1	39.11
2.2861	2	39.38
2.2800	2	39.49
2.1621	4	41.74
2.1233	23	42.54	42.52	200
2.0531	2	44.07
2.0187	1	44.86
1.9815	2	45.75
1.9746	2	45.92
1.9270	1	47.12
1.8897	1	48.11
1.8440	2	49.38
1.8253	1	49.92
1.8111	1	50.34
1.7908	1	50.95
1.7720	4	51.53
1.7524	7	52.15
1.7335	49	52.76	52.77	211
1.6990	3	53.92
1.6871	2	54.33
1.6673	3	55.03
1.6626	3	55.20
1.6502	1	55.65
1.6252	1	56.28
1.6078	1	57.25
1.5278	1	60.55
1.5111	3	61.29
1.5025	9	61.68	61.75	220
1.4951	3	62.02
1.3651	2	68.70
1.3532	1	69.39
1.3481	10	69.69	70.02	310
1.3356	2	70.44
1.3235	1	71.18

^aCalculated on the basis of a body centered cubic cell with a =4.2458 (1) Å.

Fig. 10.

x-ray precession photograph of the bcc distorted phase (Mo radiation).

3.3.4. “Ca₅Bi₁₄O₂₆” (C₅B₁₄-5:14)

A compound with the composition Ca₅Bi₁₄O₂₆ was previously reported [21,22] as stable up to at least 650 °C. We have no contrary evidence and indeed an apparently single phase x-ray diffraction pattern can be obtained for the 5:14 ratio (26.32% CaO; Fig. 11, Table 11) by annealing a quenched liquid of this composition overnight at 650 °C. The exact composition should be regarded as provisional, however, pending a crystal structure determination. The x-ray pattern in Table 11 corresponds well with that published in [22] except for a small but consistent shift in observed d amounting to ~1/4° 2θ for CuKα radiation. Apparently the earlier work had an unrecognized deviation in calibration of the diffraction data. The diffraction pattern has not yet been indexed even with the aid of some single crystal data (Fig. 12). The complexity of the pattern and consideration of the single crystal data suggests tri-clinic symmetry.

Fig. 11.

X-ray powder diffraction pattern for the Ca₅Bi₁₄O₂₆ compound.

Table 11.

X-ray powder diffraction data for the compound Ca₅Bi₁₄O₄₁

d obs (Å)	Rel I(%)	2 θ obs	2 θ calea	hkl
9.840	3	8.98	8.96	011
8.972	4	9.85	9.83	110
8.316	1	10.63	10.62	101
8.133	1	10.87	10.85	111
7.419	1	11.92	11.90	002
7.279	1	12.15	12.14	020
6.932	1	12.76	12.74	012
6.632	1	13.34	13.33	$\overline{1}11$
6.549	1	13.51	13.49	$\overline{1}11$
6.334	1	13.97	13.97	012
6.307	1	14.03	14.03	$\overline{12}1$
5.690	1	15.56	15.55	121
5.521	1	16.04	16.04	022
4.849	1	18.28	18.26	030
4.800	1	18.47	18.46	211
4.782	1	18.54	18.56	031
4.593	2	19.31	19.29	122
4.537	7	19.55	19.54	$01\overline{3}$
			19.55	$2\overline{1}1$
4.467	1	19.86	19.85	031
4.3143	3	20.57	20.58	$\overline{1}03$
4.2429	1	20.92	20.94	123
4.2150	1	21.06	21.08	122
4.1298	1	21.50	21.49	$11\overline{3}$
4.0736	2	21.80	21.81	222
3.9277	2	22.62	22.60	$21\overline{2}$
3.8620	2	23.01	22.99	230
3.7652	2	23.61	23.63	$2\overline{1}2$
3.6838	13	24.14	24.11	141
			24.16	$22\overline{0}$
3.6525	5	24.35	24.33	$22\overline{2}$
3.5576	11	25.01	24.99	203
3.5534	9	25.04	25.06	223
3.4903	16	25.50	25.51	142
3.4308	8	25.95	25.97	$1\overline{3}2$
3.4063	13	26.14	26.15	$10\overline{4}$
3.3336	2	26.72	26.71	$21\overline{3}$
3.3178	4	26.85	26.85	$\overline{2}22$
3.2997	8	27.00	27.00	310
3.2877	8	27.10	27.11	033
3.2293	75	27.60	27.61	$1\overline{3}3$
3.1347	100	28.45	28.47	$0\overline{4}2$
3.1272	72	28.52	28.53	034
3.1112	97	28.67	28.69	214
3.0744	94	29.02	29.02	$32\overline{1}$
3.0539	8	29.22	29.24	$12\overline{4}$
3.0195	9	29.56	29.55	$1\overline{4}2$
2.9743	7	30.02	30.01	$\overline{2}23$
2.9361	2	30.42	30.41	$3\overline{1}1$
2.9323	2	30.46	30.44	$2\overline{2}3$
			30.48	115
2.9285	2	30.50	30.51	$31\overline{2}$
2.9053	4	30.75	30.74	$\overline{2}32$
2.8662	2	31.18	31.17	025
2.8422	1	31.45	31.47	$2\overline{1}4$
2.8212	1	31.69	31.69	$3\overline{1}2$
2.7997	2	31.94	31.94	$05\overline{1}$
2.7777	2	32.20	32.19	$14\overline{3}$
17718	2	3127	3125	303
2.7250	96	32.84	32.84	$11\overline{5}$
			32.86	252
2.6971	50	33.19	33.21	$32\overline{1}$
2.6369	2	33.97	33.99	$\overline{3}03$
2.5976	2	34.50	34.52	$2\overline{2}4$
2.5766	2	34.79	34.79	253
2.5426	1	35.27	35.27	$\overline{3}13$
2.5371	1	35.35	35.36	$\overline{2}42$
2.4861	1	36.10	36.10	154
2.4584	2	36.52	36.54	420
2.4391	2	36.82	36.81	061
2.4276	3	37.00	36.99	$\overline{2}34$
			37.01	060
2.4057	6	37.35	37.34	261
2.4001	5	37.44	37.41	422
2.3964	4	37.50	37.48	$0\overline{1}6$
			37.51	$0\overline{5}3$
2.3523	3	38.23	38.24	$22\overline{5}$
2.3185	4	38.81	38.78	$3\overline{3}2$
2.3088	4	38.98	39.00	$43\overline{1}$
2.3008	3	39.12	39.11	216
2.2952	6	39.22	39.20	$2\overline{2}5$
2.2929	6	29.26	39.29	$4\overline{1}1$
2.2896	3	39.32	39.32	$\overline{1}26$
			39.32	423
2.2868	5	39.37	39.38	$25\overline{3}$

^aCalculated on the basis of a triclinic cell, $\mathrm{P}\overline{1}$, a =9.934(1), b = 15.034(2), c = 15.008(2) Å, α = 82.65(1), β =85.27(1), and γ = 77.17(1)°.

Fig. 12.

X-ray precession photographs of Ca₅Bi₁₄O₂₆ (Mo radiation) (a) (hOl) unfiltered μ = 10°, (b) (hOl) Zr filter (c) alternate plane, unfiltered.

At 732 ± 7°C the 5:14 phase decomposes to a mixture of the rhombohedral phase plus CaBi₂O₄ (1:2). This equilibrium was demonstrated by both the breakdown of single phase material after heating above this range, and by nucleation of 5:14 in a two phase mixture of rhombohedral + 1:2 below it. This is considerably lower than the value of 772 °C which may be interpreted from [21] (Fig. 3).

3.3.5. CaBi₂O₄ (CB₂-1:2)

The compound CaBi₂O₄ was synthesized at 650 °C [22] and reported as stable up to about 800 °C [21] where it was shown (Fig. 3) to decompose to fcc plus 2:3. Apparently inconsistent data in our own work required us to determine the decomposition temperature by simultaneous quenching of single phase 1:2, originally prepared by annealing at 650 °C, and reheating a sample of quenched liquid from which fcc plus 2:3 was synthesized. These experiments suggest that the 1:2 phase is not stable above 778 ± 5 °C. This may be compared with the value of 799 °C which can be interpreted from [21] (Fig. 3). The 1:2 phase often occurs along with other phases in samples that are air quenched from temperatures greater than about 800 °C. The x-ray powder diffraction pattern of the 1:2 phase Fig. 13, Table 12, corresponds well with that reported in [22] except for the observed shift in 2 θ mentioned in section 3.3.4. Several attempts were made to synthesize single crystals of the 1:2 phase (see Table 1b), but the only procedure that succeeded was to anneal single phase 1:2 + a 50/50 NaCl/KCl flux (50/50 flux/charge) at 775 °C and then cool at 1 °C/h to 645 °C. The single crystal x-ray diffraction precession data are shown in Fig. 14. The x-ray powder diffraction pattern was indexed on the C-centered monoclinic cell C2/c obtained from the single-crystal precession data. The lattice parameters refined by least-squares analysis with the aid of calculated structure factors and the calculated powder pattern based on single crystal structure determination are a = 16.6295(8), b = 11.5966(5), c = 14.0055(6) Å, and β = 134.036(3)°.

Flg. 13.

X-ray powder diffraction pattern of the CaBi₂O₄ compound.

Table 12.

X-ray powder diffraction data for the compound CaBi₂O₄ (CaO:l/2Bi₂O₃ 33:67)

d obs (Å)	Rel I(%)	2 θ obs	2 θ calea	hkl	|F| cale
8.847	4	9.99	9.98	$11\overline{1}$	35
8.324	2	10.62	10.62	110	27
5.977	7	14.81	14.81	200	79
5.802	2	15.26	15.27	020	32
5.282	2	16.77	16.77	111	32
5.029	5	17.62	17.60	002	15
5.018	5	17.66	17.64	021	46
4.957	1	17.88	17.85	$31\overline{2}$	14
4.7413	6	18.70	18.70	$22\overline{1}$	56
4.4316	6	20.02	20.03	$22\overline{2}$	57
		21.442:3
3.8179	20	23.28	23.27	$11\overline{3}$	78
3.8018	31	23.38	23.38	022	130
3.7700	11	23.58	23.59	310	19
3.6808		24.16	24.18	130
3.6029	2	24.69	24.68	112	31
3.4308	5	25.95	25.95	$40\overline{4}$	79
3.3546	9	26.55	26.53	$42\overline{2}$	58
3.3385	14	26.68	26.67	$31\overline{4}$	81
3.3312	15	26.74	26.77	$13\overline{2}$	78
3.3190	8	26.84	26.83	221	42
3.2723	42	27.23	27.24	$20\overline{4}$	247
3.2374	8	27.53	27.52	131	72
3.1941	22	27.91	27.89	$51\overline{3}$	117
3.1631	100	28.19	28.21	$33\overline{2}$	276
3.0859	12	28.91	28.92	$33\overline{1}$	78
3.0817	12	28.95	28.96	$42\overline{1}$	59
		29.332:3
2.9879	48	29.88	29.87	400	289
2.9503	16	30.27	30.25	$33\overline{3}$	87
			30.28	311	74
2.9053	2	30.75	30.76	023	14
2.8970	1	30.84	30.82	040	5
2.8502	2	31.36	31.67	$22\overline{4}$	43
2.8178	5	31.73	31.75	$11\overline{4}$	65
2.7853	14	32.11	32.10	041	16
2.7769	17	32.21	32.24	330	22
2.7470	30	32.57	32.57	$60\overline{4}$	234
2.7058	44	33.08	33.07	132	209
2.6705	5	33.53	33.53	$24\overline{2}$	46
			33.53	$51\overline{5}$	38
2.6559	2	33.72	33.71	420	31
2.6559	6	33.90	33.92	222	17
2.6422	5	33.96	33.97	$31\overline{5}$	18
2.6086	1	34.35	34.35	240	24
2.5882	1	34.63	34.61	$33\overline{4}$	18
2.5567	1	35.07	35.04	$60\overline{2}$	23
2.5198	18	35.60	35.58	$42\overline{5}$	106
2.5185	15	35.62	35.64	004	135
2.4821	1	36.16	36.15	$62\overline{4}$	22
2.4552	1	36.57	36.56	$53\overline{2}$	15
2.4494	1	36.66	36.63	$24\overline{3}$	19
2.4359	3	36.87	36.89	$53\overline{4}$	49
2.3933	1	37.55	37.53	331	41
2.3708	2	37.92	37.93	$44\overline{2}$	43
2.3618	2	38.07	38.06	312	28
2.3571	3	38.15	38.14	241	42
2.3411	6	38.42	38.42	$62\overline{2}$	77
2.3271	5	38.66	38.67	$71\overline{4}$	59
2.3014	1	39.11	39.11	$22\overline{5}$	23
2.2957	1	39.21	39.23	$40\overline{6}$	40
2.2857	2	39.39	39.67	$15\overline{1}$	32
2.2762	2	39.56	39.55	150	42
2.2669	2	39.73	39.73	$44\overline{1}$	46
2.2500	5	40.04	40.02	133	68
2.2377	6	40.27	40.27	$53\overline{5}$	91
2.2177	3	40.65	40.64	$33\overline{5}$	58
2.1934	2	41.12	41.11	043	50
2.1598	3	41.79	41.78	151	59
2.1393	5	42.21	42.21	114	75
2.1339	7	42.32	42.32	$42\overline{6}$	67
2.1272	10	42.46	42.46	$62\overline{6}$	104
2.1225	6	42.56	42.58	$62\overline{1}$	53
2.1130	5	42.76	42.77	$35\overline{1}$	81
2.0693	8	43.71	43.73	$35\overline{3}$	98
2.0466	9	44.22	44.21	332	118
		44.672:3
2.0236	2	44.75	44.75	$73\overline{4}$	26
2.0137	7	44.98	44.97	$44\overline{5}$	80
2.0112	6	45.04	45.02	$15\overline{3}$	63
2.0061	9	45.16	45.17	$80\overline{6}$	49
2.0049	12	45.19	45.20	350	90
1.9986	28	45.34	45.35	$53\overline{6}$	173
1.9936	17	45.46	45.49	600	134
1.9767	3	45.87	45.88	$73\overline{3}$	57
1.9526	8	46.47	46.46	$82\overline{5}$	98
1.9330	24	46.97	46.98	060	170
			46.98	$71\overline{7}$	126
1.9119	12	47.52	47.52	422	104
1.9100	13	47.57	47.58	$22\overline{6}$	100
1.8987	24	47.87	47.85	$33\overline{6}$	117
			47.89	061	117
1.8953	19	47.96	47.95	204	176
1.8650	33	48.79	48.79	$73\overline{2}$	231
1.8611	24	48.90	48.93	$26\overline{2}$	77
1.8459	1	49.33	49.32	351	29
1.8244	2	49.95	49.93	$11\overline{6}$	42
1.8217	2	50.03	50.00	$91\overline{5}$	35
1.8200	2	50.08	50.06	$42\overline{7}$	40
1.8105	2	50.36	50.36	243	52
		50.442:3
1.8038	5	50.56	50.54	062	66
1.7991	10	50.70	50.69	$44\overline{6}$	123
1.7805	8	51.27	51.25	$26\overline{3}$	109
1.7785	7	51.33	51.35	153	91
1.7610	3	51.88	51.89	333	54
1.7438	6	52.43	52.43	$60\overline{8}$	118
1.7282	6	52.94	52.94	$71\overline{8}$	103
1.7156	6	53.36	53.37	$80\overline{8}$	143
1.7067	5	53.66	53.66	$46\overline{1}$	102
1.6869	12	54.34	54.32	$91\overline{3}$	110
			54.34	$84\overline{5}$	109
1.6784	4	54.64	54.64	$84\overline{4}$	66
			54.65	006	48
1.6744	4	54.78	54.76	063	63
1.6640	11	55.15	55.15	$26\overline{4}$	116
1.6544	16	55.50	55.48	$93\overline{6}$	164
1.6503	15	55.65	55.62	314	108
			55.68	$84\overline{6}$	95
1.6413	4	55.98	55.95	640	70
1.6357	5	56.19	56.18	408	71
			56.20	$91\overline{8}$	60
1.6335	5	56.27	56.29	$75\overline{3}$	66
1.6319	6	56.33	56.35	$93\overline{4}$	66
1.6227	10	56.68	56.67	460	146
1.6118	5	57.10	57.09	026	110
1.6023	1	57.47	57.46	$93\overline{7}$	38
1.5959	3	57.72	57.73	171	57
1.5874	18	58.06	58.06	532	139
			58.07	154	82
1.5834	12	58.22	58.21	$75\overline{6}$	43
1.5807	12	58.33	58.33	$66\overline{4}$	130
			58.35	$66\overline{3}$	87
1.5704	2	58.75	58.77	$91\overline{2}$	37
1.5595	1	59.20	59.20	$53\overline{8}$	30
1.5573	1	59.29	59.28	$37\overline{3}$	42
1.5425	6	59.92	59.93	$66\overline{2}$	95
1.5343	7	60.27	60.25	$31\overline{8}$	117
1.5330	8	60.33	60.33	064	82
1.5311	6	60.41	60.43	$26\overline{5}$	73
1.5188	2	60.95	60.94	$93\overline{8}$	58
1.5150	4	61.12	61.12	461	84
1.5055	3	61.55	61.58	353	81
1.4969	5	61.94	61.93	$75\overline{7}$	85
1.4941	8	62.07	62.06	800	134
			62.08	11,1, $\overline{7}$	131
1.4851	4	62.49	62.52	263	75
1.4836	4	6256	62.58	404	153
1.4793	8	62.76	62.76	$62\overline{9}$	89
1.4753	8	62.95	62.97	622	93
1.4715	5	63.13	63.12	$51\overline{9}$	65
1.4692	4	63.24	63.24	$57\overline{2}$	66
1.4649	4	63.45	63.46	$57\overline{4}$	78
1.4606	4	63.66	63.65	$24\overline{7}$	51
			63.68	11,1, $\overline{8}$	61
1.4520	6	64.08	64.06	046	110
			64.10	$20\overline{8}$	136
1.4414	3	64.61	64.60	$73\overline{9}$	42
1.4374	5	64.81	64.83	$84\overline{1}$	78
1.4346	6	64.95	64.94	081	116
1.4299	8	65.19	65.18	10,2, $\overline{9}$	103
1.4295	8	65.21	65.24	$35\overline{7}$	105
1.4216	3	65.62	65.61	$95\overline{4}$	80
1.4170	6	65.86	65.88	136	130
1.4090	1	66.28	66.28	$86\overline{4}$	28
			66.29	533	25
1.4027	1	66.62	66.61	10,0, $\overline{2}$	37
			66.63	$95\overline{7}$	39
1.4010	2	66.72	66.71	11,1, $\overline{9}$	67
1.3984	2	66.85	66.86	462	58
1.3977	3	66.89	66.91	$26\overline{6}$	57
1.3942	3	67.08	67.07	065	65
1.3923	3	67.18	67.21	$86\overline{6}$	91
1.3820	1	67.75	67.73	$28\overline{3}$	49
1.3802	1	67.85	67.85	11,3, $\overline{5}$	42
1.3750	5	68.14	68.13	750	84
1.3736	6	68.22	68.23	$55\overline{8}$	73
			68.23	12,0, $\overline{8}$	138
1.3657	2	68.67	68.67	372	63
1.3631	2	68.82	68.80	10,2, $\overline{2}$	63
1.3614	3	68.92	68.92	$46\overline{7}$	43
			68.92	$93\overline{1}$	37
1.3610	3	68.94	68.95	8,2, $\overline{10}$	56
1.3540	5	69.35	69.34	354	82
			69.38	264	78
1.3465	4	69.79	69.79	$48\overline{1}$	69
1.3457	5	69.84	69.83	$86\overline{7}$	68
			69.85	$95\overline{8}$	67

^aCalculated on the basis of a monoclinic unit cell, space group C2/c, a = 16.6295(8), b = 11.5966(5), c = 14.0055(6) Å, and β = 134.036(3)°.

Fig. 14.

X-ray precession photographs of CaBi₂O₄ (Mo radiation) (a) (h0l), (b) (hll).

3.3.6. Ca₄Bi₆O₁₃ (C₂B₃-2:3)

The compound “Ca₇Bi₁₀O₂₂”, (41.176 mol % CaO) was reported in [22] and [21], and the phase diagram shown in [21] can be interpreted as indicating that it decomposes at about 848 °C. (Fig. 3 in [20]). Experiments performed in the present work (Table 1) indicate that the composition of this phase is really 2:3 (40 mol % CaO) rather than 7:10, but the decomposition temperature (Table 1 and Fig. 4) of 855 ±5 °C is in good agreement with [21]. The x-ray powder diffraction pattern of this phase is shown in Fig. 15 and recorded in Table 13. These results agree well with those in [22] (except for the shift in 2 θ previously mentioned). Single crystals of Ca₄Bi₆O₁₃ were grown both by utilizing a 50/50 NaCl/KCl flux and by reannealing a quenched liquid. The compound is orthorhombic a =17.3795(5), b =5.9419(2), c =7.2306(2) Å, with a C-centered space group, as determined from single crystal x-ray precession photographs Fig. 16) and x-ray diffraction datarefined by least squares. A complete crystal structure determination [23] including single crystal x-ray analysis, neutron diffraction Rietveld analyses, and measurements of second harmonic generation, proved that the true space group is the non-centrosymetric C2mm. The crystal structure was reported in [23] from data collected on crystals prepared in this study. A complete discussion of the indexing of this phase with comparison to the calculated powder pattern is given in [27]. The crystal structure determination [23] reveals that Bi⁺³ occurs in two coordination types with 2/3 of the Bi⁺³ ions five-coordinate and 1/3 of the Bi⁺³ ions only three-coordinate, by oxygen. Determinations of the crystal structures of more of these phases will perhaps result in a better understanding of the role played by Bi³⁺ coordination in 3- and 4-component superconductors.

Fig. 15.

X-ray powder diffraction pattern of the Ca₄Bi₆O₁₃ compound.

Table 13.

X-ray powder diffraction data for the compound Ca₄Bi₆O₁₃

d obs (Å)	Rel I (%)	2 θ obs	2 θ calea	hkl	|F| calc
8.708	13	10.15	10.17	200	250
5.629	4	15.73	15.75	110	136
4.434	1	20.01	19.99	111	45
4.346	5	20.42	20.42	400	217
4.145	47	21.42	21.40	310	571
3.614	52	24.61	24.60	002	138
3.338	52	26.68	26.69	202	118
3.0386	100	29.37	29.35	112	748
2.9987	68	29.77	29.75	510	893
2.9694	31	30.07	30.05	020	829
2.8117	8	31.80	31.81	220	306
2.7794	44	32.18	32.18	402	766
2.7250	2	32.84	32.84	312	93
2.4519	2	36.62	36.61	420	187
2.4107	1	37.27	37.28	003	103
2.3225	1	38.74	38.74	203	116
			38.74	421	45
2.3088	3	38.98	38.98	512	158
2.2952	5	39.22	39.22	022	263
2.2918	3	39.28	39.90	710	185
2.2609	12	39.84	39.85	602	501
2.2187	3	40.63	40.62	222	165
2.1717	13	41.55	41.54	800	667
2.0847	1	43.37	43.39	313	85
2.0815	1	43.44	43.46	801	35
2.0733	1	43.62	43.61	620	64
2.0291	53	44.62	44.61	422	846
1.9686	1	46.07	46.09	130	159
1.9357	4	46.90	46.92	712	227
1.8744	7	48.53	48.54	330	437
1.8625	1	48.86	48.87	802	182
1.8368	2	49.59	49.60	910	189
1.8288	1	49.82	49.79	223	81
1.8078	14	50.44	50.44	004	917
1.7991	12	50.70	50.71	622	466
1.7699	2	51.60	51.60	204	195
1.7537	11	52.11	52.11	820	602
1.7376	9	52.63	52.62	10,0,0	679
1.7285	23	52.93	52.93	132	607
1.7206	18	53.19	53.18	114	141
			53.18	530	769
1.6688	1	54.98	54.97	404	197
1.6640	2	55.15	55.16	332	149
1.6574	10	55.39	55.40	314	423
1.6373	31	56.13	56.13	912	804
1.5782	1	58.43	58.45	822	170
1.5670	1	58.89	58.92	10,0,2	93
1.5533	2	59.46	59.44	532	183
1.5486	21	59.66	59.67	514	696
			59.67	730	142
1.5446	10	59.83	59.84	024	675
1.5265	1	60.61	60.59	11,1,0	141
1.5206	3	60.87	60.88	224	232
1.5004	7	61.78	61.79	10,2,0	599
1.4857	5	62.46	62.47	040	682
1.4645	2	63.47	63.48	240	332
1.4552	1	63.92	63.93	424	185
1.4462	1	64.37	64.37	005	112
1.4262	1	65.38	65.37	205	120
1.4233	3	65.53	65.53	732	321
1.4064	2	66.42	66.41	11,1,2	221
1.4060	2	66.44	66.46	440	235
1.3896	6	67.33	67.33	804	528
1.3831	1	67.69	67.71	930	197
1.3738	1	68.21	68.20	042	210
1.3574	1	69.15	69.16	242	168
1.3445	3	69.91	69.91	12,0,2	406
1.3314	1	70.70	70.71	134	150
1.3102	10	72.02	72.03	442	593
1.3041	6	72.41	72.40	13,1,0	618
1.3008	9	72.62	72.61	334	355
1.2914	9	73.24	73.24	932	615
1.2739	1	74.41	74.43	10,2,3	67
1.2588	5	75.46	75.47	824	490
1.2530	3	75.87	75.88	10,0,4	545
1.2466	9	76.33	76.34	534	619
1.2418	4	76.68	76.71	642	375
1.2354	1	77.15	77.17	11,3,0	142
1.2261	4	77.84	77.83	840	506
1.2249	3	77.93	77.94	12,2,2	344
1.1856	1	81.04	81.04	150	162
1.1783	5	81.65	81.64	116	472
1.1740	4	82.01	82.00	14,0,2	615
1.1690	2	82.44	82.46	11,3,2	239
1.1643	2	82.84	82.86	350	411
1.1614	3	83.10	83.11	406	527
			83.11	842	176
1.1544	4	83.71	83.71	10,2,4	494
1.1476	3	84.32	84.32	044	565
1.1378	3	85.22	85.22	244	260
1.1374	3	85.26	85.28	15,1,0	386
1.1291	2	86.04	86.03	10,4,0	466
1.1265	4	86.28	86.28	152	455
1.1243	2	86.49	86.48	550	501
1.1168	1	87.22	87.23	026	213
1.1126	1	87.63	87.63	606	323
1.1082	3	88.07	88.08	13,3,0	566
			88.08	352	149
1.0983	1	89.07	89.08	934	191
1.0918	6	89.74	89.73	14,2,2	579
1.0863	1	90.32	90.33	16,0,0	167
1.0817	5	90.82	90.83	426	551
1.0736	1	91.70	91.68	552	220
1.0578	4	93.47	93.48	13,1,4	520
1.0420	1	95.34	95.34	626	303
1.0370	1	95.94	95.95	12,4,0	154
1.0277	6	97.10	97.10	136	415
1.0200	1	98.08	98.06	16,2,0	245
1.0148	3	98.77	98.77	844	426
1.0074	4	99.75	99.73	916	556
1.0001	1	100.75	100.75	15,3,0	332
0.9968	2	101.21	101.21	12,4,2	353
0.9903	1	102.13	102.13	060	478
0.9841	1	103.03	103.05	260	254
0.9787	2	103.82	103.82	354	342
0.9745	6	104.45	104.44	952	496
0.9704	3	105.08	105.06	17,1,2	405
0.9655	2	105.85	105.84	18,0,0	557
0.9627	2	106.28	106.31	15,1,4	322
0.9576	2	107.10	107.09	10,4,4	396
0.9549	3	107.55	107.56	554	431
0.9446	3	109.27	109.25	13,3,4	484
0.9327	3	111.35	111.33	462	420
0.9263	1	112.52	112.51	12,0,6	275
0.9210	3	113.52	113.50	14,4,2	473
0.9182	3	114.05	114.04	18,2,0	516
0.9148	3	114.71	114.70	446	433

^aCalculated on the basis of an orthorhombic unit cell, space group C2rara, a = 17.3795(5), b =5.9419(2), and c =7.2306(2) Å.

Fig. 16.

X-ray precession photographs of Ca₄Bi₆O₁₃ (Mo radiation), (a) (hk0), (b) (0ld).

3.3.7. Ca₂Bi₂O₅ (C₂B₂-1:1)

The compound “Ca₇Bi₆O₁₆”, (53.846 mol % CaO) was reported in [22] and [21], and the phase diagram in [21] (redrawn as Fig. 3) can be interpreted as indicating that it decomposes at about 929 °C. Experiments performed in the present work (Table 1) combined with a structure determination performed on crystals prepared in this study [24] indicate that the composition of this phase is really 1:1 (50 mol % CaO) rather than 7:6. The x-ray powder diffraction pattern of the phase shown in Fig. 17 and Table 14 agrees well with that reported in [22] (except for the shift in 2 θ noted above). Single crystal x-ray diffraction precession photographs (Fig. 18) indicate that the 1:1 compound is triclinic, and powder x-ray diffraction data [27] yield least squared values of a = 10.1222(7), b = 10.146(6), c = 10.4833(7) Å, α = 116.912(5), β = 107.135(6), γ = 92.939(6)°. The indexing of this pattern out to high angles in 2 θ could only be accomplished with the aid of calculated structure factors and the calculated powder pattern based on the single crystal structure determination reported in [24]. The structure determination reveals a unique Bi⁺³ coordination of U-shaped Bi₃O₁₁ groups with one five-fold coordinated Bi⁺³ bridging two four-fold “saw-horse” shaped polyhedra [24].

Fig. 17.

X-ray powder diffraction pattern of the Ca₂Bi₂O₅ compound.

Table 14.

X-ray powder diffraction data for the compound Ca₂Bi₂O₅

d obs (Å)	Rel I (%)	2 θ obs	2 θ calea	hkl	|F| cale
9.461	4	9.34	9.36	100	59
8.717	7	10.14	10.12	001	56
			10.16	$0\overline{1}1$	63
8.001	11	11.05	11.07	$\overline{1}01$	109
7.303	4	12.11	12.14	$\overline{1}10$	66
6.916	4	12.79	12.81	$11\overline{1}$	70
5.069	4	17.48	17.49	$11\overline{2}$	40
			17.49	$0\overline{2}1$	71
5.013	2	17.68	17.69	$0\overline{1}2$	56
4.965	1	17.85	17.87	$\overline{2}01$	31
4.721	4	18.78	18.78	200	98
4.648	16	19.08	19.09	$\overline{1}02$	191
4.421	6	20.07	20.09	020	93
4.352	3	20.39	20.41	$0\overline{2}2$	79
4.237	8	20.95	20.97	$\overline{2}11$	141
4.182	19	21.23	21.23	$12\overline{2}$	206
3.9940	10	22.24	22.24	$\overline{2}02$	146
3.9746	7	22.35	23.33	$1\overline{1}2$	104
			22.42	111b	120
3.9209	7	22.66	22.65	$2\overline{1}1$	130
3.8341	11	23.18	23.19	210	169
3.7480	1	23.72	23.69	$1\overline{2}2$	38
3.7065	4	23.99	24.00	120	103
3.5243	3	25.25	25.23	$2\overline{2}1$	81
3.5120	3	25.34	25.33	102	82
3.4957	6	25.46	25.48	$\overline{1}21$	127
3.4530	2	25.78	25.79	$22\overline{2}$	65
3.3834	2	26.32	26.31	$22\overline{1}$	37
3.3696	3	26.43	26.43	$\overline{3}01$	98
3.3571	3	26.53	26.52	$12\overline{3}$	76
3.3361	14	26.70	26.69	021	197
3.3226	8	26.81	26.80	$\overline{2}12$	88
			26.83	012	115
3.3045	11	26.96	26.96	$0\overline{3}2$	192
3.2806	6	27.16	27.13	$0\overline{1}3$	135
			27.18	023	60
3.2501	5	27.42	27.41	$1\overline{3}1$	133
3.2179	4	27.70	27.70	$\overline{2}21$	117
3.1456	8	28.35	28.33	300	127
			28.35	$13\overline{2}$	102
3.1059	54	28.72	28.74	$31\overline{1}$	471
3.0600	3	29.12	29.15	$22\overline{3}$	97
3.0006	100	29.75	29.73	$\overline{2}03$	427
			29.74	$\overline{1}30$	410
			29.77	211	116
2.9938	57	29.82	29.82	$2\overline{2}$	469
2.9099	5	30.70	30.69	003	132
2.8989	9	30.82	30.82	$0\overline{3}3$	111
2.8897	36	30.92	30.93	$1\overline{2}3$	83
			30.93	$13\overline{3}$	380
			31.09	$\overline{3}20$b	122
2.8361	36	31.52	31.49	$\overline{3}12$	228
			31.53	112	391
			31.55	$3\overline{1}1$	82
2.7828	7	32.14	32.13	$\overline{2}30$	172
			32.17	310	99
2.7519	2	32.51	32.50	202	81
2.7234	5	32.86	32.84	$3\overline{2}1$	155
2.6620	3	33.64	33.63	$\overline{3}03$	101
2.6049	1	34.40	34.38	$32\overline{3}$	68
2.5510	12	35.15	35.14	$11\overline{4}$	259
2.5336	4	35.40	35.40	$22\overline{4}$	91
			35.41	$0\overline{4}2$	95
2.5171	2	35.64	35.64	$21\overline{4}$	68
			35.65	$\overline{4}01$	72
2.5055	1	35.81	35.83	$0\overline{2}4$	86
2.4761	2	36.25	36.24	$\overline{2}31$	117
2.4500	1	36.65	36.63	$1\overline{4}1$	73
2.4333	2	36.91	36.92	013	106
2.4182	2	37.15	37.13	$41\overline{2}$	84
2.4132	3	37.23	37.24	$0\overline{1}4$	122
2.3921	5	37.57	37.55	$3\overline{2}2$	177
2.3805	1	37.76	37.75	$\overline{3}13$	79
2.3594	4	38.11	38.09	400	144
2.3271	2	38.66	38.64	$31\overline{4}$	93
2.3116	6	38.93	38.95	$33\overline{2}$	107
2.3071	10	39.01	38.99	$32\overline{4}$	138
			39.02	$2\overline{4}1$	245
2.3003	9	39.13	39.14	$41\overline{3}$	139
			39.15	$\overline{4}20$	133
2.2896	12	39.32	39.31	$14\overline{1}$	259
2.2857	11	39.39	39.39	230	158
2.2757	13	39.57	39.56	$\overline{2}21$	348
2.2658	4	39.75	39.76	$1\overline{2}4$	163
2.2484	1	40.07	40.06	$3\overline{3}2$	55
2.2192	1	40.62	40.61	$1\overline{3}4$	69
2.2083	4	40.83	40.83	$24\overline{3}$	116
2.1722	2	41.54	41.55	$33\overline{1}$	94
2.1578	3	41.83	41.84	203	146
2.1311	3	42.38	42.40	$\overline{1}23$	146
2.1055	2	42.92	42.95	$2\overline{4}3$	85
2.0765	1	43.55	43.55	$3\overline{4}1$	96
2.0558	24	44.01	44.00	$24\overline{1}$	400
			44.01	$1\overline{4}4$	207
2.0536	24	44.06	44.06	140	140
2.0326	3	44.54	44.54	$23\overline{5}$	149
			44.54	$4\overline{3}1$	198
2.0206	4	44.82	44.81	$\overline{1}141$	39
2.0167	7	44.91	44.90	$0\overline{5}2$	159
2.0154	5	44.94	44.95	502	149
			44.95	$\overline{3}32$	137
2.0087	2	45.10	45.10	321	123
1.9911	18	45.52	45.50	$0\overline{2}5$	396
1.9841	4	45.69	45.72	$32\overline{5}$	180
1.9763	4	45.88	45.87	$34\overline{3}$	168
1.9722	6	45.98	45.96	$43\overline{3}$	202
			46.11	$\overline{5}12$b	117
1.9490	2	46.56	46.54	330	103
1.9322	3	46.99	46.98	$4\overline{1}2$	123
1.9287	4	47.08	47.05	$\overline{5}03$	104
			47.10	041	158
			47.12	$51\overline{2}3$b	109
1.9081	3	47.62	47.64	$\overline{5}21$	164
1.9043	3	47.72	47.74	$43\overline{4}$	95
1.8946	3	47.98	47.99	$15\overline{4}$	124
1.8850	1	48.24	48.26	$\overline{3}41$	124
1.8462	5	49.32	49.34	$\overline{4}14$	204
			49.82	$\overline{3}05$b	102
1.8261	7	49.90	49.90	$42\overline{5}$	266
1.8112	6	50.34	50.36	$51\overline{4}$	270
1.7939	13	50.86	50.87	$5\overline{1}1$	396
1.7743	16	51.46	51.46	$\overline{2}24$	368
			51.47	$\overline{5}30$	266
1.7660	6	51.72	51.73	$3\overline{5}2$	280
1.7569	3	52.01	52.01	$\overline{3}33$	176
1.7459	3	52.36	52.36	$52\overline{1}$	156
1.7418	2	52.49	52.47	$44\overline{3}$	107
1.7388	4	52.59	52.58	$0\overline{5}5$	100
1.7349	8	52.72	52.73	$\overline{1}42$	261
1.7306	3	52.86	52.88	$\overline{4}05$	127
1.7267	7	52.99	53.01	$44\overline{4}$	300
1.7200	4	53.21	53.23	$2\overline{5}4$	177
			53.26	322b	109
			53.38	$4\overline{3}3$b	145
1.7135	4	53.43	53.45	$25\overline{5}$	223
1.7017	12	53.83	53.84	421	377
			54.12	$3\overline{5}3$b	104
			54.12	$35\overline{3}$b	118
1.6883	9	54.29	54.27	$33\overline{6}$	250
			54.28	$0\overline{6}3$	248
1.6846	4	54.42	54.40	$\overline{2}15$	108
			54.41	$14\overline{6}$	128
			54.62	232b	113
			54.66	$4\overline{1}3$b	151
1.6738	7	54.80	54.78	$1\overline{6}3$	269
			54.95	$1\overline{6}2$b	142
1.6682	16	55.00	54.98	$1\overline{5}5$	305
			54.99	042	242
			54.99	$\overline{6}11$	117
			55.06	$21\overline{6}$b	213
			55.07	412b	128
1.6643	15	55.14	55.13	$\overline{4}33$	183
			55.14	$3\overline{1}4$	386
1.6596	3	55.31	55.32	223	128
1.6530	5	55.55	55.55	$\overline{6}03$	260
1.6503	5	55.65	55.63	$\overline{1}15$	217
			55.95	$61\overline{2}$b	101
			56.06	$0\overline{4}6$b	147
1.6370	4	56.14	56.14	$11\overline{6}$	105
1.6357	5	56.19	56.18	$\overline{1}51$	231
1.6248	1	56.60	56.58	$2\overline{6}2$	110
			56.71	$4\overline{5}1$b	119
1.6201	2	56.78	56.77	$1\overline{6}4$	106
1.6172	2	56.89	56.89	105	161
1.6092	7	57.20	57.21	$\overline{4}42$	313
1.5997	4	57.57	57.56	$4\overline{5}2$	242
1.5919	2	57.88	57.87	$53\overline{5}$	154
1.5884	2	58.02	58.00	$61\overline{1}$	150
1.5846	2	58.17	58.16	$2\overline{6}1$	152
1.5797	2	58.37	58.35	133	266
			58.74	$53\overline{1}$b	111
1.5694	1	58.79	58.81	$13\overline{6}$	129
1.5672	2	58.88	58.88	$16\overline{5}$	145
1.5621	1	59.09	59.11	$2\overline{5}5$	133
1.5523	6	59.50	59.51	$62\overline{2}$	300
1.5453	2	59.80	59.82	124	159

^aCalculated on the basis of a triclinic unit cell, space group $\mathrm{P}\overline{1}$, a = 10.1222(7), b = 10.1466(6), c = 10.4833(7) Å, α = 116.912(5), β = 107.135(6), and γ = 92.939(6)°.

^bCalculated |F| greater than 100 but cannot be distinguished from nearby peaks.

Fig. 18.

X-ray precession photographs of Ca₂Bi₂O₅ (Mo radiation) (a) (hk0), (b) (h0l).

3.3.8 “C-mon” MetastablePhase ~Ca_6+xSr_{6_x}Bi₁₄O₃₃ (x → 6)

When the 1:1 phase is heated between 885 and 925 °C for 20 min to 3 h a metastable C-centered monoclinic phase is formed which may be nearly single phase [a = 21.295(4), b =4.3863(8), c =12.671(2) Å, and β = 102.74(1)°]. After overnight heat treatments, however, this phase decomposes to a “bcc” plus CaO assemblage. Comparison of the X-ray powder diffraction patterns (Fig. 19, Table 15) for this phase and for Ca_6+xSr_6−xBi₁₄O₃₃ (x ~ 4.8) indicates that it is the metastable end member extension of the stable ternary solid solution.

Fig. 19.

X-ray powder diffraction pattern comparing the “C-mon” metastable phase ~ Ca_6+xSr_6−xBi₁₄O₃₃ x → 6 to the ternary x → 0.

Table 15.

X-ray powder diffraction data for the “C-mon” Metastable Phase

d obs (Å)	Rel I (%)	2 θ obs	2 θ calea	hkl
12.405	2	7.12	7.15	001
10.419	3	8.48	8.51	200
9.009	6	9.81	9.83	$20\overline{1}$
7.219	1	12.25	12.27	201
5.221	4	16.97	16.99	$40\overline{1}$
4.865	11	18.22	18.24	202
4.489	27	19.76	19.74	$40\overline{2}$
4.447	4	19.95	19.94	401
	1	20.62b
4.109	2	21.61	21.59	$11\overline{1}$
3.7049	4	24.00	24.00	310
	5	24.07b
3.6718	8	24.22	24.23	$31\overline{1}$
3.6044	11	24,68	24.69	402
			24.69	$11\overline{2}$
3.5730	6	24.90	24.93	203
3.4491	22	25.81	25.79	112
3.4360	23	25.91	25.88	311
3.3583	11	26.52	26.53	$31\overline{2}$
3.3521	11	26.57	26.57	$60\overline{2}$
3.1576	2	28.24	28.24	601
3.1565	2	28.25	28.24	$20\overline{4}$
3.0922	3	28.85	28.87	004
3.0457	74	29.30	29.31	$51\overline{1}$
3.0406	88	29.35	29.34	$11\overline{3}$
3.0265	97	29.49	29.51	312
3.0056	100	29.70	29.59	510
			29.60	$60\overline{3}$
2.9267	69	30.52	30.50	403
2.8299	2	31.59	31.61	511
2.7989	11	31.95	31.96	204
	4	32.17CaO
2.6605	6	33.66	33.64	$80\overline{1}$
2.6101	2	34.33	34.35	$60\overline{4}$
2.6042	1	34.41	34.38	313
2.5976	1	34.50	34.52	800
2.5336	5	35.40	35.40	$20\overline{5}$
2.4715	6	36.32	36.31	005
2.4359	9	36.87	36.88	801
	9	37.34CaO
2.3541	2	38.20	38.19	$51\overline{4}$
2.3036	1	39.07	39.07	$71\overline{3}$
2.2463	2	40.11	40.10	$80\overline{4}$
			40.11	314
2.2234	3	40.54	40.51	802
2.1919	25	41.15	41.13	020
2.1593	5	41.80	41.80	021
2.1534	6	41.92	41.93	712
2.1470	5	42.05	42.08	220
2.1225	7	42.56	42.58	$11\overline{4}$
2.1102	29	42.82	42.80	$20\overline{6}$
2.0783	25	43.51	43.51	$40\overline{6}$
2.0760	27	43.56	43.54	10,0,0
2.0630	17	43.85	43.86	405
2.0223	3	44.78	44.79	$42\overline{1}$

^aCalculated on the basis of a monoclinic unit cell, C2/m, a =21.295(4), b =4.3863(8), c = 12.671(2) Å, and β = 102.74(1)°.

3.4 The System CaO-Bi₂O₃-CuO

Ternary phase relations of the system CaO-l/2Bi₂O₃-CuO have been studied at temperatures between 700 and 900 °C. No ternary compounds were discovered, but new data on the CaO-l/2Bi₂O₃ and CaO-CuO binaries have been incorporated. The ternary phase relations at 700–750 and 750–800 °C are shown in Figs. 20 and 21 respectively. There remains some uncertainty about the equilibrium phase relations involving Ca_1−xCuO₂.

Fig. 20.

CaO-Bi₂O₃-CuO 700–750 °C phase diagram.

Fig. 21.

CaO-Bi₂O₃-CuO 750–800 °C phase diagram.

To verify that the three-phase equilibria inferred from synthesis runs (products of a synthesis from CaCO₃, Bi₂O₃, and CuO) reflected equilibrium phase assemblages, various three phase mixtures of pre-made binary compounds were reacted isothermally. For example, such experiments demonstrate that a mechanical mixture of Ca₄Bi₆O₁₃+7Ca₂CuO₃+3Ca₄.₅₃₃Cu_5.467O₁₀ (bulk composition 51.80: 9.84: 38.36) is metastable with respect to a mixture of Ca₂Bi₂O₅+Ca₂CuO₃+Ca₄.₅₃₃Cu_5.467O₁₀ at 700 °C. Because the nucleation (or increase in volume fraction) of Ca_1−xxCuO₂ from binary compounds was never demonstrated at 700 °C (see Sec. 3.2.2) the possibilities of three phase equilibria including Ca₂CuO₃ (and/or Ca_1−xCuO₂) plus Bi₆Ca₄O₁₃ can not be ruled out. For example, the mechanical mixture 5Ca₂CuO₃+Ca₄Bi₆O₁₃ which has a bulk composition of 56:24:20 shows no convincing evidence of Ca_1−xCuO₂ even after six heating/grinding treatments at 700 °C.

4. Summary

A new phase diagram is presented for the system CaO-CuO with the composition of the phase Ca_1−xCuO₂ corresponding to a Ca:Cu ratio of 45.33: 54.67. This compound decomposes at ~ 755 °C in air and 835 °C in O₂. The phases previously reported as “Ca₇Bi₁₀O₂₀” and “Ca₇Bi₆O₁₆” [21,22] are really Ca₄Bi₆O₁₃ and Ca₂Bi₂O₅ respectively. X-ray powder and single crystal data are reported for almost all of the binary phases encountered. No ternary phases were found in the system CaO-l/2Bi₂O₃-CuO. Above 775 °C CuO is in equilibrium with all of the binary CaO-Bi₂O₃ phases, and this is probably true below 775 °C as well.

Biography

About the authors: Benjamin P. Burton is a Physical Scientist in the Ceramics Division of the NIST Materials Science and Engineering Laboratory. Claudia J. Rawn is currently a graduate student at the university of Arizona, and was formerly in the Ceramics Division of the NIST Materials Science and Engineering Laboratory. Robert S. Roth is currently under contract at NIST, and was formerly in the Ceramics Division of the NIST Materials Science and Engineering Laboratory. N M. Hwang is with the Korea Science and Engineering Foundation, Daejeon Chunynam, Korea, and was a Guest Scientist at NIST. The National Institute of Standards and Technology is an agency of the Technology Administration, U.S. Department of Commerce.