Unusuai behaviour of variations in lattice parameter of nickel rich Ni–Ge solid solutions with composition

Abstract

The influence of Ge concentration on the lattice parameter of Ni rich Ni–Ge solid solution has been studied via precise lattice parameter measurements obtained using computerised X-ray powder diffractometry. It has been observed that although the atomic diameter of Ge is slightly smaller than that of Ni (d_Ni = 0·249 nm and d_Ge = 0·245 nm) the addition of Ge causes a significant increase in the lattice parameter of the Ni–Ge solid solution. In the dilute solid solution the increase in lattice parameter is linear with Ge concentration but beyond 2 at.-%Ge the increase in lattice parameter deviates significantly from linearity in a negative manner. This deviation is attributed to the formation of partially ordered Ge enriched regions where Ni and Ge atoms have a strong interaction which is not the case in dilute solutions. Such an interaction reduces the specific volume of the Ge enriched regions and the overall expansion of the lattice is less than that observed in dilute solutions where all the Ge atoms are randomly distributed.

MST/1757