The crystal structures of the closely related CrSn2, NiCr5Sn12 and NiCr3Sn8 phases

Abstract

Crystals of two new phases of the compositions NiCr5Sn12 and NiCr3Sn8 were grown from a 660 °C tin melt with Ni and Cr present in equal amounts. Crystals of the new composition CrSn2 were grown from a tin melt with Cr present. The crystal structures were determined. The structure of NiCr5Sn12 (space group no. 180, P6222, a = 5.4944(4), c = 13.883(5), Z = 1) belongs to the NiMg2 structure type. NiCr3Sn8 crystallizes in the space group I4/mcm (no. 140, a = 6.6092(3), c = 5.3460, Z = 1) and is isostructural with CuAl2. CrSn2 is isostructural with CuMg2. The three structures NiCr3Sn8, CrSn2 and NiCr5Sn12 form a series: they are built up by different stackings of the same layer consisting of rows of tetragonal antiprisms. Letting A, B and C denote three orientations of this layer, each differing from the other two by a rotation of 2π 3, NiCr3Sn8 is a simple AA′A sequence, CrSn2 is an ABA′B′A stacking and NiCr5Sn12 corresponds to the sequence ABCA. Adjacent layers are connected via hexagons, and the structure models may be idealized with respect to this figure. The parameters of the idealized structures agree well with the real structures. Show more