Thermoelectric performance of intermetallic FeGa3 with Co doping

• From the resistivity study of Fe1−xCoxGa3 (0.005 ⩽ x ⩽ 0.5), the metallic behavior is observed for the compounds with Co content of x ⩾ 0.125.
• The Seebeck coefficient of these compounds has contribution from both diffusion thermoelectric power and phonon-drag effect.
• A reduction in Seebeck coefficient with Co doping is observed, due to the modification in band gap and density of states at the Fermi level.
• Low-temperature lattice thermal conductivity of FeGa3 is suppressed significantly by Co doping due to the phonon-point-defect scattering.
• The maximum ZT value of ∼0.05 is achieved for Fe0.95Co0.05Ga3 at 400 K, ten times higher than that of the parent FeGa3.

Investigation on temperature-dependent electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) of intermetallic Fe1−xCoxGa3 (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 Fe0.95Co0.05Ga3, and increased further with temperature to the value of about ∼0.05 at 400 K.