Polarized light studies of the ferroelastic domains of K₃Fe₅F₁₅

Abstract

The orthorhombic ferroelastic domains of K₃Fe₅F₁₅, with prototypic tetragonal tungsten bronze(TTB) structure and mixed valency 3Fe²⁺/2Fe³⁺, have been studied at R.T. in polarized light on single crystals grown by high temperature solution growth with subsequent quenching from 973K. The birefringent ferroelastic domains exhibit a remarkable linear dichroism. The principal refractive indices and the principal extinction coefficients have been measured along the crystallographic axes, identified by means of x-ray measurements on a single domain. The correlation between the refractive indices, the extinction coefficients and the cell parameters has been established. The change of orientation of the vibration ellipse of the transmitted light due to dichroism has been observed.