Stacking disorder in metastable NiSn4

•Growth of metastable NiSn4 in Sn/Ni diffusion couples produced in different ways•Clarification of the crystal structure of NiSn4•Modelling of X-ray diffraction patterns of faulted NiSn4 fully explaining the observed patterns•Critical review of previously published reports on NiSn4

The atomic structure of NiSn4 intermetallic forming at ambient temperature in different types of Sn/Ni diffusion couples was investigated by powder X-ray diffraction. The recorded diffraction patterns show narrow Bragg reflections as well as characteristic broad diffraction bands indicative of stacking disorder in the crystal structure of NiSn4. The crystal structure consists of NiSn4layers with square-antiprismatic coordination of Ni by Sn. The stacking of these layers is irregular (faulted) by being an intermediate between the pseudotetragonal PtSn4- (space group Aeaa) and the tetragonal β-IrSn4-type (space group I41/acd) ideal structures. Thereby, the shape of the diffraction bands reveals that the stacking more closely corresponds to β-IrSn4- than to the PtSn4-type. The obtained lattice parameters are: a(β-IrSn4) = a(PtSn4) = b(PtSn4) = (6.248 ± 0.001) Å and 2c(PtSn4) = c(β-IrSn4) = (23.001 ± 0.004) Å. Pronounced stacking corresponding to a PtPb4-type structure discussed in the literature is not present in NiSn4 on the basis of the diffraction data. The latter finding is compatible with density functional theory (DFT) based first-principles calculations, indicating a higher energy for PtPb4-type NiSn4 as compared to PtSn4- and β-IrSn4-type NiSn4.

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