Electrocaloric Effect Of Pb(Zr_0.2Ti_0.8O₃ And Pb(Zr_0.8Ti_0.2O₃ And Their Composite Thin Films

Ferroelectric dielectric materials generate refrigeration through depolarization under the adiabatic condition, namely electric effect (ECE). We take advantage of the electrocaloric effect (ECE) to develop refrigerating equipment. This equipment possesses many advantages, for example: a simple structure and small volume, simple operation and friendly to environment. The giant ECE was reported in the PZT-based thin film under a lower electric field. It has a promising future in the term of space flight and military affairs.In this paper, for 100℃-200℃refrigeration range, the one-component thin films Pb_0.7Sr_0.3(Zr_0.2Ti_0.8)O₃, Pb_0.75Sr_0.25(Zr_0.8Ti_0.2)O₃ and the composite thin films Pb_0.7Sr_0.3(Zr_0.2Ti_0.8)O₃/Pb_0.75Sr_0.25(Zr_0.8Ti_0.2)O₃(PSZT) were prepared on the Pt substrates by the sol-gel method and rapid thermal processing technology(RTA). X-ray diffraction (XRD) analysis shows that one-component PSZT thin films all form crystalline thin films of single perovskite phase by 450℃calcined and 650℃RTA. Composite films were annealed by one-step and two-step annealing, which all get single perovskite phase. The diffraction peaks intensity significantly increase for the two-step annealed films. The SEM analysis shows that the grain size of films are uniform and dense, combined with the substrate close.The ferroelectric and dielectric properties of three PSZT thin films were systematically studied. The PSZT films shows a hysteresis loop characteristics of ferroelectrics and the ferroelectric is good, the composite films owes the maximum remanent polarization and the lowest coercive field under the same applied electric field. By controlling Zr and Ti ratio and the amount of strontium doping, we adjusts effectively PSZT films Curie temperature to the desired range. For the three thin-film dielectric temperature spectrum tests, the Pb_0.7Sr_0.3(Zr_0.2Ti_0.8)O₃ films shows typical ferroelectric dielectric temperature spectrum characteristics, phase change occurs at a temperature point, showing a sharp peak, the Pb_0.75Sr_0.25(Zr_0.8Ti_0.2)O₃ films and composite films don't show sharp peaks, while showing a very wide flat peak, indicating that the films exhibit diffuse phase transition, with the relaxation.The ECE of three PSZT thin films were evaluated. The value of temperature change was calculated by Thermodynamic equation. The three films all appear the maximum heating temperature change near their curie points. The composite films possess a wider effective ECE temperature range.