High-Pressure Effect on the Ferroelectric-Paraelectric Transition in PbTiO3

The crystal structure of lead titanate PbTiO3 was investigated by energy dispersive X-ray diffraction at high pressures up to 4 GPa in a temperature range of 300-950 K. At the ambient conditions, the PbTiO3 structure is tetragonal with the space group P4mm (ferroelectric phase). A structural phase transition into the cubic phase with a space group Pm (3) over barm is observed at T = 747 K. It was found that the phase transition temperature decreases upon applying the high pressure with the coefficient dT(C)/dP = -65 K/GPa. Dependences of parameters and volume of the unit cell on the pressure and temperature was found, and the bulk modulus and thermal expansion coefficients for the tetragonal and cubic phases of lead titanate have been calculated.