Thermoelectric performance of tellurium and sulfur double-substituted skutterudite materials

Two series of skutterudite materials, Co₄Sb_11.3Te_0.7−x S _x (x = 0.07–0.2) and Co₄Sb_12−x S _x (x = 0.07–0.15), were synthesized through solid state reaction and consolidated by spark plasma sintering. The samples were characterized by powder X-ray diffraction, electron probe analysis, and measurements of electrical conductivity, Hall coefficient, Seebeck coefficient, and thermal conductivity. The results indicate that sulfur in Co₄Sb_12−x S _x most likely forms the CoSbS compound and is unlikely to get into the CoSb₃ lattice, while it can dissolve in Co₄Sb_12−x Te _x compounds due to the radius compensation when fabricated by the methods in this study. The lattice thermal conductivity decreases from 2.07 Wm⁻¹ K⁻¹ for tellurium single-doped Co₄Sb_11.3Te_0.7 to 1.46–1.67 Wm⁻¹ K⁻¹ for Co₄Sb_11.3Te_0.7−x S _x (x = 0.07–0.20) at 800 K. The thermoelectric performance is significantly enhanced by tellurium–sulfur co-doping in Co₄Sb_11.3Te_0.7−x S _x compounds, and a peak dimensionless figure of merit ~1.1 is achieved in Co₄Sb_11.3Te_0.63S_0.07. The enhancement is mainly attributed to the great reduction of the lattice thermal conductivity due to the increased phonon scattering by the sulfur defect.