Metal-metalloid exchange in the Zr 1− xM xMo 2 (M ≡; Ge, Si, Al) system

Abstract

An extensive study of the possibility of substituting zirconium in ZrMo 2 by germanium, silicon or aluminium was carried out using X-ray diffractometry and metallography. In the Zr 1− x Ge x Mo 2 system the crystal structure of the prototype compound ZrMo 2 (cubic Friauf-Laves phase; space group, Fd3 m) was retained up to the composition Zr 0.8Ge 0.2Mo 2. Substitution in the Zr 1− x Si x Mo 2 and Zr 1− x Al x Mo 2 systems was possible up to the compositions Zr 0.75Si 0.25Mo 2 and Zr 0.3A1{0.7}Mo 2, respectively, but the cubic crystal structure transformed into a hexagonal MgZn 2-type structure (space group, P6 3 mmc ). This structure was stabilized if the substituent contents were in excess of 5 at.% Si or 6.7 at.% Al. A high temperature b.c.c. ternary solid solution was also observed in all the systems investigated. The unit cell parameters, cell volumes and interatomic distances were determined for the observed phases of all three systems. Some semiquantitative correlations of these phases with those found in the related Hf 1− x M x Mo 2 (M ≡; Ti, Ge, Si, Al), Zr 1− x Ti x Mo 2, Zr 1− x M x W 2 and Hf 1− x M x W 2 (M ≡; Ti, Si, Al) systems were also made.