An off-center ion near a Ba site in BaTiO3 as studied by EPR under uniaxial stress

In BaTiO3 a paramagnetic defect is identified by EPR which is attributed to a paramagnetic S=1/2 ion off-center near a Ba site. Twelve magnetically distinguishable sites contribute to the angular dependence pattern of the spectra, each of the sites being characterized by an orthorhombic g-tensor. The relative occupations of the sites change under uniaxial stress in a manner consistent with the model. The features of the center are highly characteristic for the indicated off-center position, as revealed by comparison with the previously identified Ti3+ near a Sr2+ site in SrTiO3. On the basis of the principal values of the g-tensor the paramagnetic ion can be identified with Ni. It is discussed that Ni1+ is the most likely charge state.