Phase transition energetics and thermodynamic properties of ferroelectric PbTiO3

The ferroelectric phase transition in polycrystalline PbTiO3 was investigated using differential scanning calorimetry and high-resolution x-ray diffraction. The specimen studied was a highly crystalline powder sample carefully prepared by the solution-gelation synthesis technique. The behavior of the excess specific heat, excess enthalpy, excess entropy, and spontaneous tetragonal deformation near the Pm3m <-> P4mm transition was examined. The thermal evolution of the thermodynamic order parameter as obtained from the specific heat measurements was compared to that determined from the behavior of the spontaneous elastic strain. The coefficients of the relevant Landau potential for lead titanate were deduced from these data. The results provided additional information regarding the basic thermodynamic properties of lead titanate and confirmed that a simply formulated Landau-Devonshire polynomial, having temperature independent higher-order dielectric stiffness coefficients, affords a satisfactory and self-consistent description of the single-domain ferroelectric behavior.