Static atomic displacements of Sn in disordered NiAs/Ni2In type HT-Ni1+delta Sn

摘要

The crystal structures of the intermediate solid solution HT (high temperature) Ni1+deltaSn with delta = 0.28, 0.52 and 0.61 (refined Ni contents) have been analyzed in detail by X-ray diffraction on single crystals. The previously reported basic atomic arrangement, i.e., a NiAs/Ni2In structure type (P6(3)/mmc Ni(1) on 2a, 000, Ni(2) with an occupancy delta on 2d, 2/3 1/3 1/4, and Sn on 2c, 1/3 2/3 1/4), is confirmed. However, strong anisotropic atomic displacements Occur for Sn within the a-b plane of the hexagonal unit cell, which require a Gram-Charlier expansion of the probability density function of Sri in order to obtain a good fit to the diffraction data. Direction, magnitude and the concentration dependence of the displacements can be interpreted in terms of the geometrical requirements of the different local atomic configurations in the planes z = +/- 1/4, so that the displacements can be identified as static ones. (C) 2003 Elsevier Inc. All rights reserved. [References: 20]