Dielectric and pyroelectric properties of ferroelectrics

The dielectric and pyroelectric properties of ferroelectrics were studied by measuring the temperature and electric field dependence of their dielectric constants and pyroelectric coefficients. Three types of ferroelectrics, classified according to the nature of the order parameters describing their phase transitions, are included: (1) proper ferroelectrics in which the order parameter is the electrical polarization; (2) improper ferroelectrics, in which the order parameter is not the polarization, and the spontaneous polarization arises from a nonlinear coupling of the polarization to the order parameter; and (3) pseudoproper ferroelectrics, in which the order parameter is also not the polarization, but the coupling with the polarization is linear. It is shown that the small dielectric anomalies of improper and pseudoproper ferroelectrics yield an important advantage in infrared detection and pyroelectric energy conversion. But the large Curie constants of proper ferroelectrics are advantageous in thermodielectric energy conversion.