Induced Nonstoichiometric Effects of Sb in P-Type Skutterudite Thermoelectrics

Sublimation of antimony (Sb) during synthetic processes can be fatal to the thermoelectric (TE) properties of MT4Sb12 (M: filler atoms; T = Fe, Co, Ni)-based skutterudite (SKD). In this study, the nonstoichiometric effects of Sb on the phase structure formation and, thereby, on the TE properties of p-type SKD with Nd0.9Fe3.5Co0.5Sb12+x compounds were systematically investigated. Research is carried out with x values varying from -0.8 to 1.0, and samples are prepared by combining induction melting and melt-spinning, followed by a spark plasma sintering (SPS) process. The analysis showed that the Sb-deficiency formed NdSb and FeSb2 secondary phases along with the SKD main phase, while the Sb-excess effectively sup -pressed the FeSb2 phase formation and a small amount of the Sb phase appeared at a high Sb-excess level. The appearance of the secondary phases induced by Sb nonstoichiometry directly affected the change in the filling fraction of Nd in the SKD crystal structure, which led to the carrier concentration change. Our results demonstrate that the TE performance of MT4Sb12-based compounds can be significantly changed by the Sb nonstoichiometry, which should be profoundly considered along with other strategies to improve the TE efficiency of Sb-based SKD materials.(c) 2023 Published by Elsevier B.V.