Shift of the first-order transition in RbCaF3 under hydrostatic pressure

We have investigated the Oh1 to D4h18 structural phase transition in RbCaF3 under hydrostatic pressure by monitoring the electron-paramagnetic resonance lines of Gd3+ (S=72) on Ca2+ sites. We find the first-order transition temperature shifts linearly by (3.60.1) deg/kbar but neither the amount of the first-order discontinuity nor its character is altered up to the highest pressure ph=1.2 kbar we attained. The present experiment, which does not break the symmetry, confirms a uniaxial-stress experiment of Buzaré et al., who reached a tricritical point at t=0.19 kbar, and attributed it to the symmetry-breaking stress effect on the highly anisotropic cubic fluctuations which induce the first-order transition. © 1980 The American Physical Society.