Boosting Thermoelectric Performance by Controlled Defect Chemistry Engineering in Ta-Substituted Strontium Titanate

Inspired by recent research results that have demonstrated appealing thermoelectric performance of A-site cation-deficient titanates, this work focuses on detailed analysis of the changes in performance promoted by altering the defect chemistry mechanisms. The series of cation-stoichiometric SrTi 1– x Ta x O 3±δ and A-site deficient Sr 1- x /2 Ti 1– x Ta x O 3-δ compositions (0.05 ≤ x ≤ 0.30) with cubic perovskite-like structure were selected to demonstrate the defect chemistry engineering approaches, which result in promising electric and thermal properties. High power factors were observed in compositions where appropriate concentration of the charge carriers and their mobility were attained by the presence of strontium- and oxygen vacancies and suppressed formation of the oxygen-rich layers. Noticeable deviations from stoichiometric oxygen content were found to decrease the lattice thermal conductivity, suggesting good phonon scattering ability for oxygen vacancies, vacant A-sites, and oxygen-excessive defects, while the effect from donor substitution on the thermal transport was less pronounced. The obtained guidelines for the defect chemistry engineering in donor-substituted strontium titanates open new possibilities for boosting the thermoelectric performance, especially if followed by complementary microstructural design to further promote electrical and thermal transport.