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

Abstract

The electron spin resonance of Gd³⁺ has been studied in the orthorhombic and rhombohedral phases of BaTiO₃. The main features of Gd³⁺ resonances are summarized in their relation to Fe³⁺ resonances as follows: (1) The axis of the axial crystalline field in the orthorhombic phase is parallel to the ⟨110⟩ polar axis for Gd³⁺, while this axis is parallel to ⟨001⟩ for Fe³⁺. (2) The magnitude of the axial crystalline field parameter remains almost constant through the three ferroelectric phases for Gd³⁺, while this magnitude for Fe³⁺ almost vanishes in the rhombohedral phase. To explain these differences the electric field gradients at the Ba²⁺ site were calculated and plausible models for the array of the induced electric dipole moments in the surrounding oxygen ions were discussed. Measurements on Eu²⁺ have been also performed in the powder samples of BaTiO₃.