A squeeze on the perovskite structure improves the thermoelectric performance of Europium Calcium Titanates
Polycrystalline Eu 1-x Ca x TiO 3-d (0 < x < 1) samples were synthesised to investigate the interrelations among the crystal structure, local structural disorder, and thermoelectric properties. The Ca 2+ 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 Eu 3+ (instead of Eu 2+ ). The lattice imperfections induced by Ca 2+ 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 Eu 0.2 Ca 0.8 TiO 3-d is enhanced by almost 100% compared with that of the pristine EuTiO 3 . This work demonstrates that controlling lattice deformation offers new ways to enhance the thermoelectric performance of titanates.