Anomalous behaviour of ferroelectric ceramics in paraelectric phase

The dielectric permittivity and the pyroelectric current have an anomalous behaviour in the paraelectric phase for many ferroelectric ceramics. The mechanism that leads to this behaviour, as measured at a single frequency for polycrystalline PbTiO(3)-PbZrO(3)-PbCuNbO(3) prepared by the hot-pressing method, is analysed. For high temperatures the permittivity increased instead of decreasing in accordance with the Curie-Weiss law. The pyroelectric current shows a gradual increment in the paraelectric state because conduction processes (electrons and ions) influence the dielectric losses. The complex impedance plane representation was used for measurements at frequencies from 5 Hz to 500 kHz.