Changes of birefringence and fine structure tensor in KSc(MoO4)2 induced by ferroelastic phase transitions

Abstract

Phase transitions in KSc(MoO4)2 doped with Cr3+ are studied by the electron paramagnetic resonance and birefringence techniques in the temperature range covering the three ferroelastic phases. The study is aimed at showing in what way a morphic birefringence in the ferroelastic phases in KSc(MoO4)2 may relate to the deformation of the coordination surroundings of Sc3+ ion seen in this crystal via changes of the fine structure tensor D. Based on the motion of oxygen atoms of the MoO4 groups constituting the environment of Sc3+ions, a new model of the crystal structure deformation on transition from the ferroelastic phase II to the phase III is built. This model accounts for the morphic birefringence and changes in the orientation of the optical indicatrix axes in KSc(MoO4)2.