The unit-cell dimensions of phases of Cu, Ag or Au with the CsCl structure

Abstract

The unit-cell dimensions of phases with the CsCl structure that contain Cu, Ag or Au(A) are examined as a function of the diameters of the component atoms, D A and D B and compared with those of phases of other A components. The cell dimensions of phases with upper composition of the B component limited by an electron concentration of 1.5 electrons per atom are controlled by the A – B contacts. The cell dimensions of phases containing the rare earths (B) are controlled by the A – B and B−B contacts acting cojointly. The Li and Mg phases of Ag and Au have unusually small cell dimensions. Whereas the Ag and Au phases with composition limited by electron concentration 1.5 have the same cell sizes, the Li, Mg, Sc, Y and rareearth phases of Au have cell sizes on the average 0.051 Å smaller than the Ag phases. This is accounted for in terms of the electronegativity differences for this group of Au phases. The Au phases of the alkali metals are discussed; the size of the Au − ion is deduced; the essential metallic nature of AuLi is demonstrated, and the non-existance of AuNa and AuK is rationalized. The AgMg phase with a range of homogeneity, is particularly considered.