Effects of trilinear symmetry breaking on the Potts-model transition of uniaxially stressedSrTiO3

A Landau analysis shows that a break of trilinear symmetry in the continuous three-state Potts model with linear and quadratic symmetry breaking is relevant for the trigonal-to-pseudotetragonal phase transition in uniaxially stressed ${\mathrm{SrTiO}}_3$ along [1+δ 1+δ 1-2δ], and that the effects of quartic symmetry breaking are vanishingly small. The shift of the tricritical stress parameter ${\delta }_t$ is large enough to mask fluctuation corrections to ${\delta }_t$/${\delta }_c$ in d=4-ε dimensions, and a number of quantitative results for the phase diagrams are obtained.