  We explore a material design strategy to optimize the thermoelectric power
factor. The approach is based on screening the band structure changes upon a
controlled volume change. The methodology is applied to the binary silicides
and germanides. We first confirm the effect in antifluorite Mg2Si and Mg2Ge
where an increased power factor by alloying with Mg2Sn is experimentally
established. Within a high-throughput formalism we identify six previously
unreported binaries that exhibit an improvement in their transport properties
with volume. Among these, hexagonal MoSi2 and orthorhombic Ca2Si and Ca2Ge have
the highest increment in zT with volume. We then perform super-cell
calculations on special quasi-random structures to investigate the possibility
of obtaining thermodynamically stable alloy systems which would produce the
necessary volume changes. We find that for Ca2Si and Ca2Ge the solid solutions
with the isostructural Ca2Sn readily forms even at low temperatures.
