Electron Spin Resonance of Gd³⁺ in Orthorhombic and Rhombohedral Phases of BaTiO₃

The electron spin resonance of Gd 3+ has been studied in the orthorhombic and rhombohedral phases of BaTiO 3 . The main features of Gd 3+ resonances are summarized in their relation to Fe 3+ resonances as follows: (1) The axis of the axial crystalline field in the orthorhombic phase is parallel to the <110> polar axis for Gd 3+ , while this axis is parallel to <001> for Fe 3+ . (2) The magnitude of the axial crystalline field parameter remains almost constant through the three ferroelectric phases for Gd 3+ , while this magnitude for Fe 3+ almost vanishes in the rhombohedral phase. To explain these differences the electric field gradients at the Ba 2+ site were calculated and plausible models for the array of the induced electric dipole moments in the surrounding oxygen ions were discussed. Measurements on Eu 2+ have been also performed in the powder samples of BaTiO 3 .