ESR Study of Orthorhombic Fe³⁺ Centers in Sr₂Ta₂O₇ and Sr₂Nb₂O₇

Abstract

Electron spin resonance spectra of Fe³⁺ in single crystals of Sr₂Ta₂O₇ and Sr₂Nb₂O₇ have been investigated at 180°C and 250°C, respectively. The spectrum of Sr₂Ta₂O₇ is attributed to four orthorhombic Fe³⁺ centers. Two of them show a super-hyperfine splitting at the liquid nitrogen temperature. Other two centers are also observed in Sr₂Nb₂O₇ at 250°C. Angular dependence of the spectra are described by a spin Hamiltonian with second order terms, D and E. The ratios of E to D and the directions of the principal axes for these centers are determined. Brief discussion on the site assignment of these Fe³⁺ centers is given.