EPR OF THE Gd**3** plus minus O**2** minus PAIR AS A PROBE TO ESTABLISH THE PHASE DIAGRAM OF (111)-STRESSED RbCaF//3.

Abstract

RbCaF//3 undergoes a slightly first-order structural phase transition (SPT) (T//c congruent 195 K) from the cubic O//h**1 to the tetragonal D//4//h**1**8 space group connected with CaF//6 octahedra rotation. Previously, this SPT was investigated by monitoring the EPR lines of the Gd**3** plus minus O**2** minus center substituted to a Ca**2** plus minus F** minus bond. Here, we report EPR investigations of (111)-stressed RbCaF//3:Gd**3** plus minus O**2** minus providing accurate measurements of order-parameter components and clear determination of the phase symmetries which corroborate firmly the theoretically predicted phase diagram.