Analysis of point defects in polycrystalline BaTiO3 by electron paramagnetic resonance

Several paramagnetic point defects in BaTiO3 polycrystals were detected and identified using the electron paramagnetic resonance technique. Polycrystalline samples sintered in a reducing atmosphere showed a broad signal with a giromagnetic constant of 1.932. This signal, observed only in conducting ceramics, was assigned to Ti3+ and its related complexes. VBa and VTi defects were found at giromagetic constants of 1.974 and 2.004, respectively. The EPR intensity of these defects increases after oxidising at T>1000°C. The appearance of the VBa and VTi signals in EPR spectra of oxidized ceramics correlates with the onset of the PTCR effect. At donor dopant levels ≥0.3at.%, the concentration of VBa and VTi shows 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.