Critical Behaviour of (1 + δ, 1 + δ, 1 - 2δ)-Stressed RbCaF₃: Experimental Evidence for Effects of Symmetry-Breaking Perturbations on the Three-State Potts Model

In [111]-stressed RbCaF3 above the critical end point, a three-state Potts first-order line separates a pseudo-tetragonal from a trigonal phase. By monitoring the EPR spectrum of the Gd3+-O2 pair in RbCaF3, we find that for a sufficiently large (1 + δ, 1 + δ, 1 - 2δ) symmetry-breaking stress (δ ȦA 1), this first-order transition becomes critical via a tricritical point for δ<0 and is terminated in a critical point if δ>0. © 1989 IOP Publishing Ltd.