Control of electrical to thermal conductivity ratio for p-type La_xFe₃CoSb₁₂ thermoelectrics by using a melt-spinning process

In this work we improved the thermoelectric figure of merit ZT in a La_xCoFe₃Sb₁₂ (x = 0.80, 0.85, 0.90) skutterudite system by applying a conductivity ratio (electrical to thermal) control method based on the phonon-glass electron-crystal (PGEC) approach. Polycrystalline bulks of La_xCoFe₃Sb₁₂ were prepared by melt-spinning and subsequent spark plasma sintering. Based on the thermoelectric transport properties and microstructural analysis, we found that large amount of La-filler (x ≥ 0.9) in the La_xCoFe₃Sb₁₂ system is necessary to increase the conductivity ratio required to improve the thermoelectric properties in the La_xCoFe₃Sb₁₂ system. Resultantly, the maximum ZT value of 0.87 was obtained at 723 K in the heavily filled La_0.9CoFe₃Sb₁₂. We discuss our results on the basis of the filling level dependence of the rattling effect and on the formation of the skutterudite single phase. We also confirm that a large amount of La-filling level is necessary to meet the electrical neutrality condition of the p-type La_xCoFe₃Sb₁₂ skutterudite system.