Controlling the A-site deficiency and oxygen vacancies by donor-doping in pre-reductive-sintered thermoelectric SrTiO3 ceramics

Oxygen vacancies are intrinsic defects in ABO 3 perovskite structures, and the reductive sintering of SrTiO 3 ceramics combined with donor-doping can create mobile carriers and/or vacancies at A-site to improve their thermoelectric performance. By scanning and transmission electron microscopy analyses, A-site deficiency was detected in undoped and donor-doped SrTiO 3 ceramics, reaching 19% of A-site vacancies by co-doping La, Ce and Nb respectively into A- and B-sites. Titania with mixed Ti 4+ /Ti 3+ cations were commonly detected as intergranular phases of Ti 4+ 1− m Ti 3+ m O 2− m /2 , which amounts to 17 vol.% in the undoped SrTiO 3 , thus revealing their inheritance from the pre-reductive nano-powders via liquid-phase sintering. Oxygen and A-site vacancies are both detectable by cathodoluminescence analysis from either the nano-powders or sintered phases, which reveal that mixed-donor-doping creates more vacancies at A-site, together with more oxygen vacancies to form Schottky pairs. The combination of pre-reductive sintering and mixed-donor-doping creates abundant vacancies as electronic defects in SrTiO 3 , while carrier transport were not hindered through the grain boundaries which enables zT value of an oxide to exceed 0.38 at 1000 K.