Table 1.

Crystal structure refinement details for (U,Pu)(Al,Fe)₃C₃.

Crystal data
Formula	(U0.59(5)Pu0.41(5))(Al0.54(2)Fe0.46(2))3C3*
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	100 (1)
a, b, c (Å)	3.4111 (7), 5.8987 (12), 17.499 (4)
β (°)	90.12 (3)
V (Å3)	352.10 (12)
Z	2
Calculated density (g cm−3)	7.480
Radiation type and wavelength (Å)	Synchrotron, λ = 0.71075
μ (mm−1)	40.498
Crystal dimensions (mm)	0.004 $\times$ 0.004 $\times$ 0.004
Reflections for cell refinement	1018, 2.27–20° 2θ

Data collection
Crystal description	Black triangular wedge
Diffractometer	Dectris EigerX 16 M
Scan type	φ scan with frame widths of 0.1°; counting time per frame of 0.01 s
Beam size (with at half maximum)	~ 20 µm
θ (°) range	2.328–24.692°
Indices range of h, k, l	h: ± 4, k: ± 6, l: ± 20
Absorption correction	Multi-scan SADABS (Bruker, 2001)
Tmin, Tmax	0.2854, 0.4342
No. of measured, independent and observed [I > 2σ(I)] reflections	1747, 288, 213
Rint	0.0601
Data completeness to 24.692° θ (%)	100

Refinement
Number of reflections, parameters, restraints	288, 37, 0
R1[F2 > 2σ(F2)], R1(all)	0.0298, 0.0367
wR2[F2 > 2σ(F2)], wR2(all)	0.0758, 0.0787
GoF (F2)	0.947
Δρmin, Δρmax (e Å−3)	− 1.34, 1.24

Data processing
The intensity data sets were processed using XDS38, XPREP39 and SADABS40, finding 1747 reflections with an Rint of 0.0601. Atomic positions were located using SHELXT-2018/341, and then refined anisotropically using SHELXL-2018/342 using neutral atomic scattering factors

*U/Pu ratio could not be refined from XRD and was determined from semi-quantitative EDS analysis from numerous points on the phase of interest (see SI dataset 2).