Defect Chemistry of Donor-Doped and Undoped Strontium Titanate Ceramics between 1000° and 1400°C

The electrical conductivity, sigma, of donor-doped and undoped strontium titanate (SrTiO₃) ceramics and, in some cases, single crystals, Sr1-xLaxTiO₃ (0 ≤ to x ≤ 0.1), was investigated in the temperature range of 1000°-1400°C under oxygen partial pressures, PO₂, of 10_-20-1 bar. In conjunction with Hall data and thermopower data from related papers, a set of constants for a defect-chemical model was determined, precisely describing point-defect concentrations and transport properties of these materials. In contrast to former works, temperature-dependent transport parameters and their non-negligible influence on the determination of the constants was considered, as well as the equilibrium restoration phenomena of the cation sublattice, which can be studied only at such high temperatures. It was shown that defects in the cation sublattice completely govern the electrical behavior of donor-doped and undoped SrTiO₃. In the latter case, frozen-in strontium vacancies act as intrinsic acceptors, determining the sigma(PO₂) curves at lower temperatures. This intrinsic acceptor concentration also can be calculated with this model. The very good agreement between calculation and measurement is shown in many examples.