Nonstoichiometric disorder in single-crystalline BaTiO 3 at elevated temperatures

Abstract

The electrical conductivity of single-crystalline BaTiO 3 was measured over the temperature range 800–1200°C while in thermodynamic equilibrium with oxygen partial pressures from 10 0 to 10 −19 atm. The behavior was consistent with the presence of barium and oxygen vacancies, due to the inherent BaO deficiency of the crystal, combined in the form of neutral defect complexes. The n-type electrical conductivity indicated the formation of additional, fully ionized oxygen vacancies while the p-type disorder resulted from the partial filling of oxygen vacancies present to compensate the accidental acceptor impurity content. This model takes into account two factors which are commonly ignored in ternary oxides: (1) Deviations from ideal cation-cation stoichiometry may result in substantial concentrations of defects; (2) in close-packed structures with multivalent cations and substantial band gaps, the enthalpies of formation for intrinsic defects are so unfavorable that impurity-related defects will be dominant in the near-stoichiometric region.