Use of effective field theory to predict relationships among ferroelectric parameters

The two level dipolar effective field model of ferroelectiicity, as discussed by Devonshire, gives a relationship between macroscopic ferroelectric parameters that can readily be tested: [image omitted] where P0 is the T = 0 polarization, υ is the volume per dipole, Cc is the Curie constant, k is Boltzman's constant, and ε0 = 8.85 × 10-14 F/cm. Although the mode] applies only to second-order order-disorder type of ferroelectric behavior, the above relationship holds approximately for a wide variety of ferroelectrics including first and second order displacive and order-disorder types of transitions. Classical lattice dynamic effective field theory, as treated by Lines, predicts all of these types of ferroelectric behavior, depending on the shape of the potential describing the soft mode behavior. In this theory, the above relationship holds approximately for all possible potential shapes. The relationship can be used to explain the near constancy of material figures-of-merit for pyroelectric and electro-optic devices.