Preparation And Study On Electrocaloric And Energy Storage Effect Of Plzst-Basted Ferroelectric Thin Film

Ferroelectrics have many forms of existence,such as ceramics,single crystals,polymers,polycrystalline films and so on.Compared with their ceramic materials,ferroelectric thin films have more excellent electrical properties.Among of them,ferroelectric/antiferroelectric thin/thick films with large electrocaloric（EC）effect have a strong attraction in solid-state cooling devices.PLZST-basted ferroelectric thin film,which has excellent ferroelectric,piezoelectric,pyroelectric and other properties,is a typical multifunctional material.And it has potential application prospects in micro actuators,energy storage capacitors,ferroelectric memories and sensors and other devices.In this paper,relaxor Pb_0.97La_0.02(Zr_0.905Sn_0.015Ti_0.08)O₃（PLZST）thin film deposited on a LaNiO₃/Pt（111）/Ti/SiO₂/Si composite electrode was successfully designed to locate at a morphotropic phase boundary（MPB）with a coexistence of ferroelectric trigonal,antiferroelectric tetragonal and antiferroelectric cubic phases by using multilayer crystallization annealing of a sol-gel method.The microstructure and the electrocaloric refrigeration performance of the PLZST thin film under different oxygen annealing processes were systematically investigated.On this basis,the electrocaloric refrigeration property of PLZST thin films doped with Mn prepared by layer-by-layer/multilayer crystallization annealing on different substrates were further studied.The results are as follows:（1）In the process of oxygen annealing/non annealing,the phase structures of the four kinds of thin films are significantly different,which is mainly reflected in that the thin films deposited directly on the LaNiO₃/Pt composite bottom electrode or the thin films annealed by oxygen are mainly tetragonal/orthorhombic antiferroelectric phase while the thin films deposited on the LaNiO₃/Pt composite bottom electrode annealed by oxygen and the thin films annealed again are mainly rhombohedral ferroelectric phase.This phenomenon can be attributed to the fact that the phase structure of the thin film near the three-phase composition point is exceedingly sensitive to the change of the stress state of the bottom electrode.The thin film deposited on the oxygen annealed LaNiO₃/Pt composite bottom electrode,which the temperature change value（ΔT）of the electrocaloric refrigeration near the room temperature is about 20.3 K and the full width at half maximum（FWHMΔT）of the refrigeration temperature range is approximately 80 K,shows the first-class electrocaloric refrigeration performance.After aging for one year of the thin film,its temperature change value of the electrocaloric refrigeration can be significantly increased from 20.3K to 40.2 K,which increased about double.（2）The PLZST thin films doped with Mn deposited on LaNiO₃/Pt（111）/Ti/SiO₂/Si composite bottom or Pt（111）/Ti/SiO₂/Si bottom by multilayer/layer-by-layer crystallization annealing method show a typical hard ferroelectric structure and increase dielectric loss.The PLZST thin films doped with Mn deposited on LaNiO₃/Pt（111）/Ti/SiO₂/Si composite bottom,p-GaN bottom or Pt（111）/Ti/SO₂/Si bottom all are pure perovskite structure.The PLZST thin films deposited directly on LaNiO₃/Pt（111）/Ti/SiO₂/Si composite bottom by multilayer crystallization annealing method exhibited better energy storage characteristics,which its energy storage density（W）is 13.3J/cm³ and the energy storage efficiency（η）is 60.8%under the electric field test condition of 1285.7kV/cm,and the temperature stability is good in the range of 20℃ to 200℃.