Trigonal-to-tetragonal transition in stressed SrTiO3: A realization of the three-state potts model

The trigonal-to-pseudotetragonal structural first-order transition in [111]-stressed SrTiO3 is shown to be a realization of the continuous three-state Potts model. The measured order-parameter discontinuity at the transition, Δ →, depends on the trigonal order parameter [111] M as |Δ →||M|δ*, with δ*=0.62±0.10 (mean-field theory predicts δ*=1). This agrees with renormalization-group predictions, and proves that the model has a first-order transition even in the fluctuation-dominated region. © 1977 The American Physical Society.