From random stacking faults to polytypes: A 12-layer NiSn₄ polytype

NiSn₄ grows in diffusion couples (Ni plates with electrodeposited Sn) in a temperature range from room temperature up to 353 K. Previously, the crystal structure of NiSn₄ grown at ambient temperature was identified to be an intermediate stacking variant between the orthorhombic PtSn₄-type and the tetragonal β-IrSn₄-type structure, with a slight tendency towards the tetragonal type (Schimpf et al., Mater. Design 109 (2016) 324–333). Now it is reported that NiSn₄ forming at 333 K and above, exhibits a 12-layer polytype (space group P4₂/nbc, a = b = 6.250 Å c = 69.00 Å) due to ordered incorporation of stacking faults into the structure. This NiSn₄ structure was derived by comparison of its diffraction patterns with those of the exhaustively generated NiSn₄ polytypes. First-principles calculations on a series of selected NiSn₄ polytypes demonstrate that the experimentally observed polytype is energetically favoured as compared to others.