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.