Thermodynamics and ferroelectric properties of KNbO3

Abstract

The Landau–Ginzburg–Devonshire phenomenological theory is employed to model and predict the ferroelectric phase transitions and properties of single-domain potassium niobate (KNbO3). Based on the LGD theory and the experimental data of KNbO3 single crystal, an eighth-order polynomial of free energy function is proposed. The fitted coefficients are validated by comparing to a set of experimental measured values including phase transition temperatures, spontaneous polarization, dielectric constants, and lattice constants. The effects of hydrostatic pressure and external electric field on phase transition temperatures and piezoelectric coefficients are investigated. The free energy function may be used to predict ferroelectric domain structures and properties of KNbO3 bulk and films by phase-field approach.