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Multi-Site and Multi-Ionization of Sn in the Doping of BaTiO3



This article considers the diverse substitutional effects of the Sn cations in the BaTiO3 lattice and its impact on the electrical conduction as a function of A/B stoichiometry, oxygen partial pressure, and temperature. High-density specimens were fabricated in the different oxygen partial pressures to control the valence state of Sn ion. Specifically, the nonstoichiometric materials were sintered in a low pO2 atmosphere (10−14 atm at 1320°C) and in a high pO2 atmosphere (10−0.21 atm at 1320°C), respectively. It is found that Sn occupying the Ti-site acts as an acceptor dopant, and the electronic conductivity varies from a n-type to p-type transition, with increasing oxygen activity as mostly expected. However, there is an unusual case noted with Sn doping the A-site where the conductivity, σ, is invariant at high pO2's, i.e., σ ~ math formula with m ≈ 0 in the high pO2 regime. The variation of the conductivity is explained by a valence changing of Sn ion from +2 to +3 to +4 with increasing oxygen partial pressure, and we model this data across all conditions within a self-consistent defect chemistry model.