Thermal expansion anisotropy and site occupation of the pseudo-binary molybdenum vanadium silicide Mo5Si3–V5Si3

The coefficients of thermal expansion (CTEs) and atomic site occupation factors were measured for the pseudo-binary molybdenum–vanadium silicide Mo5Si3–V5Si3. The ratios of the CTEs in the crystallographic c and a directions range from 2.0 for Mo5Si3 to 1.2 for Mo2V3Si3. The metal atoms can occupy chain sites (in the crystallographic c-direction), and non-chain sites. The relatively small V atoms prefer the chain sites in Mo5Si3, whereas the relatively large Mo atoms prefer the non-chain sites in V5Si3. These site-occupation characteristics reduce the thermal expansion in the c-direction and thereby the CTE anisotropy. Ab initio calculations for Mo4VSi3 suggest that, energetically, V prefers the chain sites, while the measurements show that V occupies also non-chain sites. Extrapolation of the experimental results assuming the site-occupation used in the calculations agrees with the theoretical result that the thermal expansion of Mo4VSi3 is isotropic.