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Electrocaloric properties in relaxor ferroelectricElectro-caloric effect in PLZT (8/65/35) ceramic AIP Conf.

The objective of this work was to examine linear thermal expansion of K 0.5 Na 0.5 NbO 3 ceramics between room temperature and 790°C by contact dilatometry. The material was single phase with 95.5% relative density and with a uniform microstructure. Three distinct regions of thermal expansion could be discerned, corresponding to the three phases of K 0.5 Na 0.5 NbO 3 : monoclinic (assuming a single perovskite unit cell), tetragonal, and cubic, separated by discontinuities as typical for the first-order phase transitions. The linear coefficient of thermal expansion between 30°and 195°C is 2.96 3 10 À6 K À1 , between 208°and 364°C is 4.35 3 10 À6 K À1 , and between 434°and 790°C is 7.52 3 10 À6 K À1 . †

Stoichiometric K0.5Na0.5NbO3 solid solution(KNN) was prepared by solid-state synthesis from alkaline carbonates and niobium oxide. Thermal decomposition of the powder mixture occurs upon heating to 700 °C followed by crystallization of the perovskite phase. After sintering at 1100 °C, 2h the stoichiometric KNN reaches 94 % of theoretical density. Dielectric constant of stoichiometric KNN is 620, and the losses 0.03.

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