Preparation And Study On Energy Storage And Electrocaloric Effect Of BCZT-Based Relaxor Ferroelectric Thin Films

Ferroelectric thin films are widely used in dielectric storage capacitors,solid-state cooling devices and displacement devices due to the better electrical properties than bulk ceramic materials.In this paper,the three-phases(cubic,tetragonal and rhombohedral phases)coexisting component point 0.68BZT-0.32BCT(abbreviated as pure BCZT)in the phase diagram of pseudobinary ferroelectric system Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 was chosen to be the basic component of[(Ba0.904Ca0.096)0.9775+xLa0.015(Zr0.136Ti0.864)O3,x =0.0075,0.075 and 0.15](abbreviated as La-doped BCZT)dielectric relaxor thin film capacitors prepared by using a sol-gel method.The effects of A-site excess,type of bottom electrodes and the size of top electrodes on the microstructure and energy storage properties of pure BCZT and La-doped BCZT films were systematically investigated.Moreover,La-doped BCZT(x = 0.0075)(abbreviated as BCLZT)thin films possessing the best comprehensive energy storage performance and Pb0.8Ba0.2ZrO3(abbreviated as PBZ)thin films are composited to prepare BCLZT/PBZ multilayer thin films.The effects of different bottoms on the microstructure and electrocaloric effect of BCLZT/PBZ multilayer thin films were investigated.The results are as follows.(1)The large energy storage density(W?15.5 J/cm3),ultra-high efficiency(??93.7%)and high thermal stability(the variation of both W from 20 0C to 260? and ? from 20? to 140? is less than 5%)have been simultaneously achieved in the La-doped BCZT(x = 0.0075)lead-free relaxor ferroelectric thin film capacitors deposited on LaNiO3/Pt composite bottom electrodes.The good energy storage property of the La-doped BCZT(x = 0.0075)thin film capacitors is mainly ascribed to the diversity of the structure of the nano-clusters around the three-phases coexisting component point,as well as the ultra-high quality of thin film due to the utilization of the LaNiO3/Pt composite bottom electrode.The relationship between top electrode area and energy storage performance indicates that W value of the La-doped BCZT(x = 0.0075)deposited on LaNiO3/Pt composite electrode is 0.7 J/cm3,and the ? value is still as high as 91.4%when the area of Pt top electrode has been increased to?7.079 mm2.Morever,Its energy storage performance will be further improved with the optimization of the top electrode quality.(2)Both the BCLZT/PBZ multilayer thin films deposited on the Pt and LaNiO3/Pt composite bottom electrodes exhibit the pure perovskite structures.In addition,the utilization of LaNiO3/Pt composite bottom improves the dielectric properties and electrocaloric of BCLZT/PBZ multilayer thin films.When the operation electric field is 756 kV/cm,the ?T for BCLZT/PBZ multilayer thin films deposited on the Pt and LaNiO3/Pt composite bottom electrodes at room temperature are 6.6 K and 20.4 K,respectively.