Improved thermoelectric properties in heavily doped FeGa3

FeGa3, a hybridization gap semiconductor, has been substituted with an n-type dopant Ge to form a series of compositions FeGa3-xGex. Electrical and thermal transport properties of these compositions have been studied. Change in carrier density (n) is evident from the Hall measurements. The carrier density (n) can be as high as similar to 10(21) cm(-3) in these compositions. In order to study the role of heavy doping on the thermoelectric properties of FeGa3, an alloy series Fe1-yCoyGa3-xGex has also been synthesized with higher concentrations of Ge (x=0.1-0.35) and Co (y=0.1-0.5). From resistivity and Seebeck coefficient measurements, it appears that heavy doping is accomplished by the simultaneous substitutions of Ge and Co. The systematic change in both resistivity (rho) and Seebeck coefficient (alpha) is possibly due to change in the carrier density (n). The power factor (PF) alpha(2)/rho improves steadily with increasing carrier density and the best PF similar to 1.1 mW/ m K-2 is observed for the heavily doped compositions at 875 K. In the alloy series Fe1-yCoyGa3-xGex, thermal conductivity is also reduced substantially due to point defect scattering. Due to higher power factors, the figure of merit ZT improves to 0.25 at 875K for the heavily doped compositions. (C) 2015 AIP Publishing LLC.