Influence of local crystal structure and grain size on electronic transport properties of (La1/2K1/2)TiO3-based thermoelectric ceramics

Abstract

We investigated the influence of the local crystal structure and microstructure on the electronic transport properties of (La1/2K1/2)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.