Dielectric and polarization measurements on ${\mathrm{BaTiO}}_3$ at high pressures to the tricritical point

Dielectric and polarization measurements were made on single crystal ${\mathrm{BaTiO}}_3$ in a hydrostatic medium to 38 kbar. The nature of the ferroelectric phase transition is observed to go from first to second order near 35 kbar and -40 °C. The pressure–temperature–electric-field phase diagram of ${\mathrm{BaTiO}}_3$ is measured. The tricritical point is indicated in this part of the phase diagram by a change in shape of both the real and imaginary parts of the dielectric response as the material passes through the cubic to tetragonal phase transition in zero electric field and by the pressure dependence of the critical points at the ends of the paraelectric-to-ferroelectric phase lines.