Several paramagnetic point defects in BaTiO3 polycrystals were detected and identified by using the electron paramagnetic resonance technique. Polycrystalline samples sintered in a reducing atmosphere showed a broad signal with a gyromagnetic constant of 1.932. This signal, observed only in conducting ceramics, was attributed to Ti3+ and its related complexes. VBa and VTi defects were found at gyromagnetic constants of 1.974 and 2.004, respectively. The electron paramagnetic resonance intensity of these defects increased after oxidizing at T > 1000C. The appearance of the VBa and VTi signals in electron paramagnetic resonance spectra of oxidized ceramics correlates with the onset of the PTCR effect. At donor dopant levels above 0.3at%, the concentration of VBa and VTi showed good agreement with the defect compensation mechanism of donor doped BaTiO3. However, small amounts of VBa and VTi were also detected in undoped BaTiO3, contrary to the generally accepted defect model.

Analysis of Point Defects in Polycrystalline BaTiO3 by Electron Paramagnetic Resonance. T.Kolodiazhnyi, A.Petric: Journal of Physics and Chemistry of Solids, 2002, 64[6], 953-60