Donor-acceptor charge complex formation in barium titanate ceramics: Role of firing atmosphere

BaTiO(3) ceramics containing Mn accepters and various Mo, W and Nb donor dopants have been fired in reducing atmosphere and re-oxidized in N(2)/O(2). In single Mn-doped ceramics, Mn(2+) is completely oxidized to Mn(3+); in N(2) containing 50 ppm O(2) at T > 800 degrees 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 accepters and donors have been observed, In donor-acceptor charge complexes, Mn(2+) cannot be oxidized.