Electrocaloric Effect Of PbZr_1-xTi_xO₃ And PbTiO₃

Ferroelectric materials and its thin films are important function materials, with perfectly ferroelectric, piezoelectric, pyroelectric, electro-optic and nonlinear optical properties. The distribution of ferroelectric materials is very wide, with more than 1000 ferroelectric crystals. Ferroelectric crystals have attracted physical academic and material attention early in 1940s. Research shows that the temperature of ferroelectric crystals in adiabatic polarization/depolarization process becomes lower/large, to refrigeration effect.Based on the Landau-Devonshire thermal dynamic theory, this paper calculated the electrocaloric effect(EC) of PbTiO3 and PbZr1-xTixO3 (x=0.5,0.6,0.7,0.8,0.9) bulk & film materials by MATLAB. Besides, it also studied the temperature and electric field dependences of the polarization near ferroelectric phase transition, the electric-entropy, the electric-entropy change, and the heat capacity.A first-order electricity(?)ferroelectric transition occurs at the Curie temperature of 769 K for PbTiO3 bulk materials. The coervice field of 25 MV/m is obtained at 700 K. Strong electric fields drives PbTiO3 block material from first order to second continuous phase transition gradually, and phase transition occurs at a higher temperature. For PbTiO3 film, the second phase transition makes entropy lower, and entropy change drop accordingly. With the increase of the electric field, the heat capacity is reduced. The temperature changes of block materials are largest at refrigeration heat capacity, the same of refrigeration heat capacity. They are 4.76 K and 94.1 kJ m-3K-1. Beside, for PTO film, the tensile stress makes the phase transition temperatures lower, and the compressive stress higher.The Curie temperatures of PZT bulk are 665 K,691 K,713 K,729 K, and 740 K, respectively. A ferroelectric(?)paraelectricity transition occurs. Strong electric fields drives PbTiO3 block material from first order to second continuous phase transition gradually, and phase transition occurs at a higher temperature. With the increase of the electric field, the heat capacity is reduced, and phase transition occurs at a higher temperature. But the entropy increases with the enhancement of electric field. With the increase of Ti content, the maximum value of entropy change increases gradually. Therefore, the maximum of electric temperature change for zirconium-rich PZT blocks is further above Curie temperatures. In other words, they have the largest MCE at 200 K above their ferroelectric(?)paraelectricity transition temperatures.