A squeeze on the perovskite structure improves the thermoelectric performance of Europium Calcium Titanates

Abstract

Polycrystalline Eu1–xCaxTiO3–δ (0 ≤ x ≤ 1) samples were synthesised to investigate the interrelations among the crystal structure, local structural disorder, and thermoelectric properties. The Ca2+ substitution is locally modifying (squeezing) the crystal structure, resulting in distinct differences between the long-range and local scales, e.g., the sample with x = 0.2 shows a cubic structure in long-range scale, while tetragonal distortions are observed locally. Additionally, the contraction of the unit cell volume with an accompanying reduction of the overall symmetry facilitates the accommodation of smaller Eu3+ (instead of Eu2+). The lattice imperfections induced by Ca2+ substitution significantly improve electron concentration and simultaneously dramatically reduce thermal conductivity (i.e., as large as 50% compared with pristine sample) at room temperature. The average thermoelectric figure of merit of Eu0.2Ca0.8TiO3–δ is enhanced by almost 100% compared with that of the pristine EuTiO3. This work demonstrates that controlling lattice deformation offers new ways to enhance the thermoelectric performance of titanates.