Thermoelectric properties of the narrow-gap intermetallic compound Ga ₂Ru: Effect of Re substitution for Ru atoms

In this paper, the effect of hole doping on the thermoelectric properties of the binary narrow-gap semiconducting intermetallic compound Ga ₂Ru in the temperature range from 373 K to 973 K was investigated. We synthesized sintered pellets by spark plasma sintering (SPS) after arc-melting and succeeded in preparing crack-free samples. The maximum dimensionless figure of merit ZT _max was 0.50 at 773 K for the sintered Ga ₂Ru alloy. The temperature dependence of the electrical resistivity and its magnitude at 373 K dramatically changed from negative (∼11,000 μΩcm) to positive (∼200 μΩcm) upon hole doping by the substitution of Re for Ru atoms. Also, the Seebeck coefficient at 373 K changed from 300 μV/K to 75 μV/K. These changes were identified by the increase in carrier concentrations observed by Hall- effect measurements. In particular, large power factors (2.0 mW/m K ² to 3.0 mW/m K ²) were obtained over a wide temperature range from 373 K to 973 K upon Re substitution. The lattice thermal conductivity beneficially decreased with increasing Re concentration as a result of an alloying effect.