Donor-Acceptor Charge Complex Formation in Barium Titanate Ceramics: Role of Firing Atmosphere

BaTiO₃ ceramics containing Mn acceptors and various Mo, W and Nb donor dopants have been fired in reducing atmosphere and re-oxidized in N₂/O₂. In single Mn-doped ceramics, Mn²⁺ is completely oxidized to Mn³⁺; in N₂ containing 50 ppm O₂ at T > 800°C. Changes of the Curie point and sample length under reduction and re-oxidation have been detected using dielectric and thermomechanical measurements. Charge compensation and complex formation between acceptors and donors have been observed. In donor-acceptor charge complexes, Mn²⁺ cannot be oxidized.