Abstract
A factor k has been introduced to denote the release effect of a BX bond along the tetragonal axis in the structural phase transition from cubic to tetragonal symmetry. With the aid of this factor, a simple relationship between the zero-field splitting D in the tetragonal phase and the spin-lattice coupling coefficient G 11 in the cubic phase for paramagnetic ions in the perovskite structure has been proposed. On the basis of this, for Gd3+ in crystalline RbCaF3, the local release factor k in the vicinity of the Gd3+ ion is determined from the stress dependence of the electron paramagnetic resonance (EPR) spectrum in the cubic phase and the EPR data in the tetragonal phase. The result is obviously different from that of the host crystal.