Effect of pressure on the zone-center phonons of PbTiO3and on the ferroelectric-paraelectric phase transition

The first-order Raman spectrum of single-crystalline PhTi${\mathrm{O}}_3$ in the teatragonal ferroelectric phase was studied at room temperature as a function of hydrostatic pressure up to 80 kbar. Mode Grüneisen parameters, as well as higher-order coefficients in the expansion of phonon frequency vs pressure are reported for all zone-center TO phonons. The pressure $P_1$ at which the ferroelectric-paraelectric (FE → PE) phase transition would occur continously can be obtained by fitting the pressure dependence of the lowest $E\left(\mathrm{T}\mathrm{O}\right)$ "soft" mode frequency with a Curie-Weiss-type law. This criterion yields $P_1=90\mathrm{}\pm 4$ kbar. Limits for the first derivative of the transition temperature with pressure are similarly obtained and yield $5.2<-\frac{d{T}_C}{\mathrm{dP}}<5.9\mathrm{}$ K/kbar. The information on the FE → PE phase transition obtained here is in good agreement with previously reported data obtained by measuring the pressure dependence of the dielectric constant in the PE phase.