The Study Of The Influence Of The Interface Effect To The Electrocaloric Effect In Compositional Graded Films

The temperature and entropy of the dielectric material can change with theapplied electric field in adiabatic condition, which is called electrocaloric （EC） effect.The EC effect has attracted great interest over the past decades because it caneffectively reduce the greenhouse gases and energy consumption and be used todomestic and industrial refrigeration.The interface effect has been proved that it can effectively improve theferroelectricity, dielectric and pyroelectricty in compositional graded ferroelectricfilms. To our known, there are no investigations of EC effect in compositional gradedferroelectric films. In this article, the EC effect of Ba1-xSrxTiO3（BST） compositionalgraded film was investigated here. And we develop a thermodynamic model toresearch the mechanism how the interface effect influents the EC effect in thecompositional graded film. The mainly research contents and obtained results in thisthesis are summarized as follows:（1）. The Experimental investigation of the electrocaloric effect in BST thin filmsThe200nm Ba_0.7Sr_0.3TiO₃/Ba_0.8Sr_0.2TiO₃/Ba_0.9Sr_0.1TiO₃compositional gradedfilm and200nm Ba_0.9Sr_0.1TiO₃films were prepared by sol-gel method. And we useMaxwell relation to calculate the eletrocaloric of their. The results reveal that the ECeffect of BST compositional graded films （ΔT=3.2K at T=290K） is larger than thatof the Ba_0.9Sr_0.1TiO₃thin film （ΔT=1.9K at T=360K）, and the Tpeakof the peak ECeffect is closer to the room temperature than the Tpeakin Ba_0.9Sr_0.1TiO₃thin film. Thesedifferences are attribute to the interface effect and a large entropy change conductedby the movement of the free charges under the control of external field.（2）. The investigation of the EC effect in the compositional graded filmA thermodynamic model was developed to investigate the influence of theinterface effect to the EC effect in the compositional graded film. The results revealthat with the increasing of the density of oxygen vacancies, the magnitude of the ECeffect would be decreased and the temperature of the peak EC effect would be shiftedto the higher temperature. Compared to the single compositional film, the interfaceeffect in compositional grade films can restrict the influence of oxygen vacancies tothe EC effect. So the EC effect in compositional graded film is bigger than that of thesingle compositional film, and nearer to the room temperature than the singlecompositional film, and these results are coincident to our experiment results.