Influence of local crystal structure and grain size on electronic transport properties of (La_1/2K_1/2)TiO₃-based thermoelectric ceramics

Abstract

We investigated the influence of the local crystal structure and microstructure on the electronic transport properties of (La_1/2K_1/2)TiO₃ (LKT) ceramics as an n-type thermoelectric material. Undoped and Nb-doped LKT ceramics were fabricated via the conventional solid-state reaction route. X-ray pair distribution function (PDF) of the undoped LKT ceramic was analyzed by reverse Monte Carlo (RMC) fitting using a supercell model containing 12 × 12 × 12 perovskite unit cells. The PDF analysis results demonstrated that the local structure of LKT resembled that of SrTiO₃ (ST), implying that LKT possessed comparable electron mobility with ST. Comparing the electrical conductivity and Seebeck coefficient between two Nb-doped LKT ceramics with different grain sizes showed that grain boundaries strongly inhibited the electronic transport in LKT ceramics. These findings suggest that grain coarsening is a key to achieving high electrical conductivity in LKT-based thermoelectric ceramics.