Thermoelectric performance of intermetallic FeGa₃ with Co doping

Investigation on temperature-dependent electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) of intermetallic Fe_1-xCo_xGa₃ (0.005 ≤ x ≤ 0.5) compounds are carried out to probe their thermoelectric performance. From resistivity study, it is observed that increase in number of valence electrons introduced by Co doping leads to a change from semiconducting to metallic behavior, which occurs between x = 0.05 and 0.125. The characteristics of the Seebeck coefficient show a substantial decrease with the Co doping, due to the modifications in the band gap and the Fermi-level density of states. Analyses of thermal conductivity of the Co doped FeGa₃ compounds reveal that thermal transport is essentially due to the lattice phonons. It is also noticed that the low-temperature peak in the lattice thermal conductivity of these compounds is reduced significantly with the increase in Co content, attributing to the enhanced scattering of phonons by point-defects. The value of the figure-of-merit, ZT = (S²/ρκ)T, is estimated for all compounds, and the maximum room-temperature ZT value of about 0.02 was achieved for Fe_0.95Co_0.05Ga₃, and increased further with temperature to the value of about ∼0.05 at 400 K.