Properties Of Energy And Electrocaloric Effect Of Nd-doped PZT Lead Based Ferroelectric Thin Films

As a typical multi-functional material,lead zirconate titanate?PZT?based ferroelectric thin films have been widely used in microelectronics,optoelectronics,capacitors for energy storage,infrared detectors,sensor and other devices because of excellent properties of ferroelectric,piezoelectric,pyroelectric.For the polarization and depolarization behaviors of ferroelectric thin films correspond to the charging and discharging process of capacitors,PZT thin films are often used as energy storage capacitors.Meanwhile,solid state refrigeration devices based on the electrocaloric effect?ECE?of ferroelectric thin films have applications in MEMS and other fields.In this paper,we prepared Zr-rich Pb_1-3x/2Nd_xZr_0.948Ti_0.052O₃ thin film with Nd-doped content of 2mol%,4mol%,6mol%,8mol%,Pb_0.97Nd_0.02Zr_xTi_1-xO₃ thin film with different Zr/Ti ratios?100/0,95/5,52/48,0/100?and Pb_0.97Nd_0.02TiO₃ thin film with different crystallization annealing time.All of them were deposited on the substrates of Pt?111?/Ti/SiO₂/Si by a sol-gel method and layer by layer crystallization annealing.The energy storage and electrocaloric effect performance are also studied.XRD phase structure and SEM morphology analysis showed that all the films were perovskite structure.Under the combined influence of highly preferred orientation substrate and layer by layer crystallization process,the film exhibits a typical?111?preferred orientation at 2? = 38.5?.Although the surface of the film exhibits a small number of microcracks,the cross-sectional structure is smooth,without obvious inter diffusion and mutual reaction.Electrical properties test and analysis calculation of thin films indicated that Nd-doped 4mol%thin film has the maximum energy storage density?20.66J/cm³?and the highest energy storage efficiency?89.2%?at room temperature.In contrast,Nd-doped 6mol%thin film has the best energy storage temperature stability.The entropy change and temperature change of Nd-doped 4mol%thin film reach the maximum value of-6.64 JK^-1kg^-1 and-8.51 K at 423K,respectively,indicating the best electrocaloric effect performance.2mol%Nd-doped PZT thin film near the morphotropic phase boundary?zirconium titanium to 52/48?has the highest energy storage density?16.90J/cm³?at room temperature.Its energy storage density changes by about 6%,showing the best temperature stability from room temperature to 150?.PZT?0/100?thin film has the maximal remanent polarization?42.18 ? C/cm²?,coercive electric field?795.75kV/cm?and rectangularity?0.8379?.Type-555?5minutes of heat treatment at 300??500? and 700?,respectively?crystalline annealed film?abbreviated PNT555?has better ferroelectric properties compared with type-333?3minutes of heat treatment at 300??500? and 700?,respectively?thin film?abbreviated PNT333?.At room temperature,the energy storage density?12.05 J/cm³?of PNT555 thin film is much larger than that of PNT333 thin film,but its temperature stability of energy storage is poor.PNT333 thin film and PNT555 thin film exhibit large leakage current due to their structural defects at high temperature and high electric field.Their electrocaloric effect performance is a large negative electrocaloric effect.