Effect of Carrier-Doping on the Thermoelectric Properties of Narrow-Bandgap (Fe,Ru)Ga₃ Intermetallic Compounds

Abstract

We have focused on the binary narrow-bandgap intermetallic compounds FeGa₃ and RuGa₃ as thermoelectric materials. Their crystal structure is FeGa₃-type (tetragonal, P4₂/mnm) with 16 atoms per unit cell. Despite their simple crystal structure, their room temperature thermal conductivity is in the range 4–5–W–m^−1–K⁻¹. Both compounds have narrow-bandgaps of approximately 0.3–eV near the Fermi level. Because their Seebeck coefficients are quite large negative values in the range 350–<–|S _373K|–<–550–μV–K⁻¹ for undoped samples, it should be possible to obtain highly efficient thermoelectric materials both by adjusting the carrier concentration and by reducing the thermal conductivity. Here, we report the effects of doping on the thermoelectric properties of FeGa₃ and RuGa₃ as n and p-type materials. The dimensionless figure of merit, ZT, was significantly improved by substitution of Sn for Ga in FeGa₃ (electron-doping) and by substitution of Zn for Ga in RuGa₃ (hole-doping), mainly as a result of optimization of the electronic part, S ² σ.