Electron paramagnetic resonance and positron annihilation study of the compensation mechanisms in donor-doped BaTiO3 ceramics

A study of the defect structure of BaTiO3-based ceramics and their correlation with the compensation mechanisms is presented. The addition of different Nb2O5, Sb2O3 or La2O3 oxide contents (ranging from 0.05 to 0.60 mol%) to commercial BaTiO3 powders allowed to obtain the sintered specimens. EPR spectroscopy was used to characterize the paramagnetic species in the crushed samples. Information regarding bulk and vacancy-like defects in the studied specimens was also obtained using positron annihilation lifetime spectroscopy. Also, complementary analysis through tetragonality parameters and measurements on the real permittivity were carried out. The obtained results show a dependence of the defect profile of the BaTiO3-based specimens on the concentration and type of additive. For high additive content samples, titanium point-like defects were detected; while barium vacancies were detected in samples with low antimony content. Furthermore, oxygen vacancies were revealed in samples with low lanthanum addition. A relationship among the doping level and defect structure is proposed. (C) 2007 Elsevier Ltd. All rights reserved.