Thermal expansion anisotropy of ternary molybdenum silicides based on Mo₅Si₃

The coefficient of thermal expansion (CTE) of the tetragonal silicide Mo₅Si₃ is highly anisotropic. The ratio of the CTE's in the c and a directions, CTE(c)/CTE(a), is approximately 2. Partial substitution of the Mo in Mo₅Si₃ by "larger" Nb or "smaller" V atoms increases or reduces the lattice parameters, respectively. In both cases the CTE anisotropy CTE(c)/CTE(a) decreases significantly and values as small as 1.25 are observed. Similar results have been reported previously for Ti₅Si₃ alloyed with "large" Zr atoms and for Zr₅Si₃ alloyed with "small" Ti atoms. These results are interpreted in terms of the site occupation of the ternary alloying additions and the resulting reductions in the anharmonicity along the c axis.