Effect of secondary LuNiSn phase on thermoelectric properties of half-Heusler alloy LuNiSb

We report on the high-temperature (350 K <T< 1000 K) thermoelectric properties of the ternary compounds LuNiSb (cubic) and LuNiSn (orthorhombic) and a composite material (LuNiSb)${}_{0.5}$(LuNiSn)${}_{0.5}$. The electrical conductivity in LuNiSn is metallic, while it is semiconducting-like in LuNiSb. The Seebeck coefficient reaches -5.5 $\mu$V/K at 700 K for the former compound and 66 $\mu$V/K at 607 K for the latter one. The composite sample (LuNiSb)${}_{0.5}$(LuNiSn)${}_{0.5}$ constructed from orthorhombic matrix with cubic inclusions combines the electrical conductivity of LuNiSn with the thermoelectric properties of LuNiSb. Nonetheless, no enhancement of the thermoelectric performance occurs for this material.