High-temperature transport properties of complex antimonides with anti-Th₃P₄ structure

Polycrystalline samples of R₄Sb₃ (R = La, Ce, Sm and Yb) and Yb_4−xR′_xSb₃ (R′ = Sm and La) have been quantitatively synthesized by high-temperature reaction. They crystallize in the anti-Th₃P₄ structure type (I3d, no. 220). Structural and chemical characterizations have been performed by X-ray diffraction and electron microscopy with energy dispersive X-ray analysis. Powders have been densified by spark plasma sintering (SPS) at 1300 °C under 50 MPa of pressure. Transport property measurements show that these compounds are n-type with low Seebeck coefficient except for Yb₄Sb₃ that shows a typical metallic behavior with hole conduction. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb_4−xR′_xSb₃ up to 0.75 at 1000 °C.