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disorder; static displacements; local atomic arrangements; crystal structure; X-ray diffraction; nickel-tin alloys; non-stoichiometric phases; intermetalics
Abstract:
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.
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