Thermodynamic theory of PbZrO3

Abstract

A thermodynamic theory is presented to model the phase transitions and properties of lead zirconate. The free energy ΔG is expressed as a power series in terms of the ferroelectric polarization (Pi=Pai+Pbi) and antiferroelectric polarization (pi=Pai−Pbi) including all possible terms up to the sixth power, but only first-order cross coupling terms and couplings to elastic stress. Under the assumption that only the lowest-order coefficients of Pi and pi are linearly temperature dependent (Curie–Weiss behavior) and all other constants are temperature independent, experimental data are used to define the constants and permit calculation of ferroelectric and antiferroelectric free energies as a function of temperature. Use of the function to define the averaged dielectric permittivity at room temperature in the antiferroelectric phase gives a value of εR=120 in good agreement with recent microwave measurements. A simplified technique for modifying the function to explore solid solution with lead titanate is examined, and shown to lead to excellent agreement with the known phase diagram.