Redetermination of EuScO₃

Abstract

Single crystals of europium(III) scandate(III), with ideal formula EuScO₃, were grown from the melt using the micro-pulling-down method. The title compound crystallizes in an ortho­rhom­bic distorted perovskite-type structure, where Eu occupies the eightfold coordinated A sites (site symmetry m) and Sc resides on the centres of corner-sharing [ScO₆] octa­hedra (B sites with site symmetry ). The structure of EuScO₃ has been reported previously based on powder diffraction data [Liferovich & Mitchell (2004). J. Solid State Chem. 177, 2188–2197]. The results of the current redetermination based on single-crystal diffraction data shows an improvement in the precision of the structral and geometric parameters and reveals a defect-type structure. Site-occupancy refinements indicate an Eu deficiency on the A site coupled with O defects on one of the two O-atom positions. The crystallochemical formula of the investigated sample may thus be written as ^A(□_0.032Eu_0.968)^BScO_2.952.

Related literature

Details of the synthesis are described by Maier et al. (2007 ▶). Rietveld refinements on powders of LnScO₃ with Ln = La³⁺ to Ho³⁺ are reported by Liferovich & Mitchell (2004 ▶). The crystal structures of the Dy, Gd, Sm and Nd members refined from single-crystal diffraction data have been recently provided by Veličkov et al. (2007 ▶). The crystal structure of the isotypic TbScO₃ is described by Veličkov et al. (2008 ▶). Specific geometrical parameters have been calculated by means of the atomic coordinates following the concept of Zhao et al. (1993 ▶).

Experimental

Crystal data

• Eu_0.968ScO_2.952

• M _r = 239.24

• Orthorhombic,

• a = 5.7554 (7) Å

• b = 7.9487 (10) Å

• c = 5.5087 (6) Å

• V = 252.01 (5) ų

• Z = 4

• Mo Kα radiation

• μ = 26.28 mm⁻¹

• T = 293 (2) K

• 0.14 × 0.12 × 0.02 mm

Data collection

• Stoe IPDS-2 diffractometer

• Absorption correction: analytical (Alcock, 1970 ▶) T _min = 0.139, T _max = 0.397

• 2168 measured reflections

• 362 independent reflections

• 345 reflections with I > 2σ(I)

• R _int = 0.055

Refinement

• R[F ² > 2σ(F ²)] = 0.021

• wR(F ²) = 0.051

• S = 1.27

• 362 reflections

• 31 parameters

• 1 restraint

• Δρ_max = 1.40 e Å⁻³

• Δρ_min = −0.84 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2006 ▶); cell refinement: X-AREA; data reduction: X-RED (Stoe & Cie, 2006 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ATOMS for Windows (Dowty, 2004 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Eu1—O1i	2.276 (5)
Eu1—O2ii	2.304 (3)
Eu1—O1iii	2.375 (5)
Eu1—O2iv	2.611 (3)
Eu1—O2v	2.845 (3)
Sc2—O2ii	2.094 (3)
Sc2—O2vi	2.107 (3)
Sc2—O1vii	2.1108 (16)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

supplementary crystallographic information

Comment

Liferovich & Mitchell (2004) studied the crystal structure of lanthanoid scandates, including EuScO₃, by Rietveld analysis from powder diffraction data. Crystallographic data of DyScO₃, GdScO₃, SmScO₃ and NdScO₃ obtained from single crystals were recently reported by Veličkov et al. (2007), and for TbScO₃ by Veličkov et al. (2008). Based on these results it was possible to resolve disagreements concerning some structural characteristics and their dependence on the Ln-substitution. Whereas Liferovich & Mitchell (2004) observed no obvious continuous evolution, Veličkov et al. (2007) were able to show that the geometry and the distortion of the sites are linearly coupled with the size of the lanthanoid in the series from DyScO₃ to NdScO₃. With the structural refinement based on diffraction data collected from single crystalline EuScO₃, the present results provide further data for this series.

The orthorhombic distorted perovskite structure for EuScO₃ (Fig. 1) is confirmed from our refinements. Whereas the lattice parameters for EuScO₃ compare well with the data of Liferovich & Mitchell (2004), the fractional atomic coordinates show deviations of up to 0.006, resulting in slightly different geometrical parameters. The A-site is occupied by Eu in an eightfold coordination and has an average bond length of ^[8]<A—O> = 2.521 Å with a polyhedral bond length distortion of ^AΔ₈ = 7.98×10^-3 (Δn = 1/n Σ{(r_i-r)/r²). The B-site shows bond lengths typical for octahedrally coordinated scandium (<B—O> = 2.104 Å) and is rather distorted with ^BΔ₆ = 0.015×10^-3 and a bond angle variance of δ = 2.61°. The tilting of the corner sharing octahedra calculated after Zhao et al. (1993) are θ = 19.70° in [110] and Ø = 12.66° in [001] directions. From our data we can establish linear trends for the crystallochemical parameters from DyScO₃ to NdScO₃ depending on the Ln-substitution.

Experimental

An EuScO₃ fiber was grown using a micro-pulling-down apparatus with induction heating (Maier et al., 2007). The starting material was prepared from 4 N Eu₂O₃ and Sc₂O₃ powders by grinding a total weight of 5 g in a plastic mortar and pressing the mixture into pellets. An 5 ml iridium crucible with 500 mg of the starting material was placed on an iridium after-heater and heated by the inductor coil of a 10 kW rf Generator. The crucible after-heater arrangement was surrounded by a zirconia fiber tube and a high-purity alumina tube for thermal insulation. The experiments were carried out in a vacuum-tight steel chamber. It was evacuated before each experiment to 5 x10^-3 mbar and filled with 5 N argon gas. Subsequently, a constant flow of about 900 ml/min was kept. During growth the height of the molten zone and consequently the diameter of the fiber (~1 mm) was carefully controlled by manually increasing or decreasing the rf-power. Several starting compositions with different Eu to Sc ratios were tested, resulting in the optimal batch with 47.5 mol% Eu₂O₃ and 52.5 mol% Sc₂O₃.

The grown single-crystal was colourless. A part of the single-crystal fiber was crushed and the irregular shaped fragments were screened using a polarizing light microscope to find a sample of good optical quality for the diffraction experiments.

Refinement

Site occupation refinements indicated deviations from full occupancy on the Eu1 (A-site) and the O2 sites. For the final refinement cycle a constraint ensuring charge neutrality was included. The crystallochemical formula of the investigated sample can thus be written as ^A(□_0.032Eu_0.968)^BScO_2.952. The highest peak and deepest hole of the difference Fourier map are located 0.84 Å and 1.42 Å away from the Eu1 position. In contrast to the previous Rietveld refinement, where the Pbnm setting of space group no. 62 was chosen, the standard setting Pnma was used for the present redetermination.

Figures

Fig. 1.

The orthorhombic perovskite structure of EuScO3 is characterized by a tilted corner sharing ScO6 framework incorporating the 8-fold coordinated Eu sites. The ScO6 octahedra are yellow, the Eu atoms are given in grey and the O atoms are presented in red.

Fig. 2.

Projection of the EuScO3 structure along [010], showing the Eu atoms and the Sc coordination with displacement ellipsoids at the 80% probability level.

Crystal data

Eu0.968ScO2.952	F(000) = 422.4
Mr = 239.24	Dx = 6.307 Mg m−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 2218 reflections
a = 5.7554 (7) Å	θ = 2.6–29.2°
b = 7.9487 (10) Å	µ = 26.28 mm−1
c = 5.5087 (6) Å	T = 293 K
V = 252.01 (5) Å3	Platy fragment, colourless
Z = 4	0.14 × 0.12 × 0.02 mm

Data collection

Stoe IPDS-2 diffractometer	362 independent reflections
Radiation source: fine-focus sealed tube	345 reflections with I > 2σ(I)
graphite	Rint = 0.055
Detector resolution: 6.67 pixels mm-1	θmax = 29.1°, θmin = 4.5°
ω scans	h = −7→7
Absorption correction: analytical (Alcock, 1970)	k = −10→9
Tmin = 0.139, Tmax = 0.397	l = −7→7
2168 measured reflections

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.021	w = 1/[σ2(Fo2) + (0.0211P)2 + 0.9412P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.051	(Δ/σ)max = 0.011
S = 1.27	Δρmax = 1.40 e Å−3
362 reflections	Δρmin = −0.84 e Å−3
31 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
1 restraint	Extinction coefficient: 0.113 (5)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Eu1	0.05854 (5)	0.25	0.01589 (6)	0.0090 (2)	0.9677 (13)
Sc2	0	0	0.5	0.0078 (3)
O1	0.4506 (8)	0.25	0.8815 (9)	0.0111 (9)
O2	0.1954 (6)	0.9378 (4)	0.8078 (6)	0.0112 (7)	0.9758 (10)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Eu1	0.0070 (3)	0.0102 (3)	0.0098 (3)	0	0.00051 (11)	0
Sc2	0.0064 (6)	0.0079 (6)	0.0090 (6)	0.0006 (6)	0.0000 (3)	0.0000 (3)
O1	0.011 (2)	0.008 (2)	0.014 (2)	0	−0.0025 (17)	0
O2	0.0096 (16)	0.0121 (17)	0.0119 (14)	−0.0019 (12)	−0.0018 (11)	0.0005 (12)

Geometric parameters (Å, °)

Eu1—O1i	2.276 (5)	Sc2—O2ii	2.094 (3)
Eu1—O2ii	2.304 (3)	Sc2—O2xii	2.094 (3)
Eu1—O2iii	2.304 (3)	Sc2—O2vi	2.107 (3)
Eu1—O1iv	2.375 (5)	Sc2—O2xiii	2.107 (3)
Eu1—O2v	2.611 (3)	Sc2—O1xiv	2.1108 (16)
Eu1—O2vi	2.611 (3)	Sc2—O1x	2.1108 (16)
Eu1—O2vii	2.845 (3)	Sc2—Eu1xv	3.2268 (4)
Eu1—O2viii	2.845 (3)	Sc2—Eu1i	3.2268 (4)
Eu1—Sc2ix	3.2268 (4)	Sc2—Eu1xvi	3.3428 (4)
Eu1—Sc2x	3.2268 (4)	Sc2—Eu1xvii	3.4841 (4)
Eu1—Sc2xi	3.3428 (4)	Sc2—Eu1xviii	3.4841 (4)
Eu1—Sc2	3.3428 (4)
O1i—Eu1—O2ii	103.43 (12)	O2xii—Sc2—O2vi	90.88 (6)
O1i—Eu1—O2iii	103.43 (12)	O2ii—Sc2—O2xiii	90.88 (6)
O2ii—Eu1—O2iii	80.77 (17)	O2xii—Sc2—O2xiii	89.12 (6)
O1i—Eu1—O1iv	87.69 (11)	O2vi—Sc2—O2xiii	180
O2ii—Eu1—O1iv	137.24 (9)	O2ii—Sc2—O1xiv	87.46 (16)
O2iii—Eu1—O1iv	137.24 (9)	O2xii—Sc2—O1xiv	92.54 (16)
O1i—Eu1—O2v	137.77 (9)	O2vi—Sc2—O1xiv	92.67 (15)
O2ii—Eu1—O2v	117.06 (6)	O2xiii—Sc2—O1xiv	87.33 (15)
O2iii—Eu1—O2v	73.38 (8)	O2ii—Sc2—O1x	92.54 (16)
O1iv—Eu1—O2v	71.14 (12)	O2xii—Sc2—O1x	87.46 (16)
O1i—Eu1—O2vi	137.77 (9)	O2vi—Sc2—O1x	87.33 (15)
O2ii—Eu1—O2vi	73.38 (8)	O2xiii—Sc2—O1x	92.67 (15)
O2iii—Eu1—O2vi	117.06 (6)	O1xiv—Sc2—O1x	180
O1iv—Eu1—O2vi	71.14 (12)	Sc2xix—O1—Sc2xv	140.6 (2)
O2v—Eu1—O2vi	69.74 (15)	Sc2xix—O1—Eu1xx	105.10 (13)
O1i—Eu1—O2vii	71.82 (8)	Sc2xv—O1—Eu1xx	105.10 (13)
O2ii—Eu1—O2vii	77.31 (12)	Sc2xix—O1—Eu1xviii	91.82 (14)
O2iii—Eu1—O2vii	155.61 (9)	Sc2xv—O1—Eu1xviii	91.82 (14)
O1iv—Eu1—O2vii	67.12 (8)	Eu1xx—O1—Eu1xviii	124.0 (2)
O2v—Eu1—O2vii	126.63 (6)	Sc2xxi—O2—Sc2xxii	143.00 (18)
O2vi—Eu1—O2vii	66.38 (5)	Sc2xxi—O2—Eu1ii	98.83 (13)
O1i—Eu1—O2viii	71.82 (8)	Sc2xxii—O2—Eu1ii	117.90 (14)
O2ii—Eu1—O2viii	155.61 (9)	Sc2xxi—O2—Eu1xxii	85.85 (11)
O2iii—Eu1—O2viii	77.31 (12)	Sc2xxii—O2—Eu1xxii	89.57 (12)
O1iv—Eu1—O2viii	67.12 (8)	Eu1ii—O2—Eu1xxii	103.48 (13)
O2v—Eu1—O2viii	66.38 (5)	Sc2xxi—O2—Eu1xxiii	88.37 (12)
O2vi—Eu1—O2viii	126.63 (6)	Sc2xxii—O2—Eu1xxiii	79.82 (10)
O2vii—Eu1—O2viii	121.45 (13)	Eu1ii—O2—Eu1xxiii	102.69 (12)
O2ii—Sc2—O2xii	180	Eu1xxii—O2—Eu1xxiii	153.77 (14)
O2ii—Sc2—O2vi	89.12 (6)

Symmetry codes: (i) x−1/2, y, −z+1/2; (ii) −x, −y+1, −z+1; (iii) −x, y−1/2, −z+1; (iv) x, y, z−1; (v) −x+1/2, y−1/2, z−1/2; (vi) −x+1/2, −y+1, z−1/2; (vii) x, y−1, z−1; (viii) x, −y+3/2, z−1; (ix) x+1/2, −y+1/2, −z+1/2; (x) −x+1/2, −y, z−1/2; (xi) −x, y+1/2, −z+1; (xii) x, y−1, z; (xiii) x−1/2, y−1, −z+3/2; (xiv) x−1/2, y, −z+3/2; (xv) −x+1/2, −y, z+1/2; (xvi) −x, −y, −z+1; (xvii) −x, −y, −z; (xviii) x, y, z+1; (xix) x+1/2, −y+1/2, −z+3/2; (xx) x+1/2, y, −z+1/2; (xxi) x, y+1, z; (xxii) −x+1/2, −y+1, z+1/2; (xxiii) x, y+1, z+1.