Pressure-induced change in the order of the phase transition in lead titanate: Structural aspects

The crystal structure of lead titanate PbTiO₃ have been studied by energy-dispersive X-ray diffraction under pressures of 0–4 GPa in the temperature range of 300–950 K. At a temperature of T = 747 K, a structural phase transition from a ferroelectric tetragonal phase to a paraelectric cubic phase is observed. The application of pressure leads to a significant decrease in the phase transition temperature; under pressures of P ∼ 2 GPa, the type of the phase transition changes from the first to second order. In the low pressure range, the baric coefficient value is dTc/dP = −20(3) K/GPa; under pressures above 2 GPa, it increases up to −113(5) K/GPa.