Preparation And Energy Storage Properties Of Lead Zirconate-based Antiferroelectric Thin Films

Dielectric capacitors are widely used in the fields of national defense,high-tech,and civilian use.The development of energy storage devices with high energy storage density and efficiency is the focus of current research in the field of energy storage media.Antiferroelectric materials are considered to be the most potential high power density energy storage dielectric materials due to their high energy storage density and fast discharge speed.Among them,the Pb Zr O₃（PZO）-based antiferroelectric material has a unique antiferroelectric-ferroelectric phase transition behavior,and has high saturation polarization and small remanent polarization at room temperature,which is an ideal antiferroelectric material matrix for energy storage.With the development of high power,integration,and miniaturization of devices,how to improve the energy storage properties of PZO-based antiferroelectrics has always been a research focus in the field of energy storage.According to the calculation formula of energy storage density,improving the breakdown strength and saturation polarization is the main method to optimize the energy storage properties of PZO thin films,and the common implementation methods include structural design and doping modification.Based on this,this thesis optimized the preparation process of PZO thin films.By designing the Pb Zr_0.35Ti_0.65O₃/Pb Zr O₃（PZT/PZO）multilayer film structure and La and Ti co-doped PLZT,the breakdown strength and saturation polarization strength were improved,and the effect of microstructure on electrical properties was further revealed.The regulation law has achieved the improvement of the energy storage characteristics of the PZO antiferroelectric thin film.The details are as follows:（1）In this chapter,the sol-gel method is used to determine the optimal preparation process of PZO-based antiferroelectric thin films,and the influence of two key process parameters,crystallization temperature and lead excess,on the energy storage properties of PZO antiferroelectric thin films is studied.It is found that when the annealing temperature is 650°C,the film has good crystallization,dense surface,small dielectric loss value,the narrowest antiferroelectric hysteresis loop,and the highest energy storage density and efficiency.Under the annealing condition of 650℃,with the increase of lead excess,the surface density of PZO film increases significantly,and the polarization intensity and energy storage density first increase and then decrease.The optimum conditions for the preparation of PZO films were determined as annealing crystallization temperature of 650℃and excess lead of 10%.（2）PZT and PZO films with large saturation polarization were selected for layered composite,and the multilayer interface structure was used to improve the electrical breakdown strength to prepare PZT/PZO multilayer films.Compared with PZT and PZO,the three films all show good perovskite phase,and the composite film has the diffraction peaks of PZT and PZO,and the diffraction peaks are weak,which may be caused by the thin film of the single layer.PZO exhibits typical antiferroelectric double hysteresis loops and dielectric double butterfly loops,PZT exhibits typical ferroelectric single hysteresis loops and butterfly loops,and PZT/PZO composite films have ferroelectric hysteresis loops and antiferroelectric double butterfly curve,careful analysis found that PZT/PZO exhibited a weak double hysteresis loop at low electric field,which may be due to the partial pressure caused by the different dielectric constants in the PZT/PZO layered composite film.When the applied electric field is small,this is mainly applied to the PZO layer,which makes the PZT/PZO samples exhibit antiferroelectric properties at low electric fields.The breakdown strengths of PZT,PZO and PZT/PZO multilayers are 1162 k V/cm（film thickness is 460 nm）,1373k V/cm（film thickness is 520 nm）and 1760 k V/cm（film thickness is 440 nm）,respectively,and the maximum energy storage densities W_rec are 8.12 J/cm³,15.32J/cm³ and 21.11 J/cm³,the maximum energy storage efficiency is 30.3%,76%and63.3%,respectively.The breakdown strength and releasable energy storage density of the multi-interface structure PZT/PZO composite film are significantly higher than the former two,which is mainly due to the fact that the multilayer heterojunction interface hinders the diffusion of the electrical tree and enhances the breakdown strength of the film.In addition,the leakage current of the PZT/PZO film is about 10 times lower than that of the PZT film,and the SCLC model of the space charge limited current of the PZT film is changed to the interface-controlled Schottky barrier SE model,indicating that the interface plays a role in reducing the leakage current.The key role also illustrates the role of the interface in improving the breakdown strength.The above experimental results prove that it is a feasible method to improve the breakdown strength E_BDS of thin films by using the multilayer structure to improve the energy storage properties.（3）We prepared Pb_0.925La_0.05Zr_1-xTi_xO₃（x=0.5%,x=1.5%,x=2.5%,x=3.5%,x=4.5%,x=5.5%）by sol-gel method.Ferroelectric thin films,all films showed good perovskite phase,no second phase appeared,PLZT films all showed obvious（111）preferred orientation,with the increase of Ti doping amount,due to the Ti⁴⁺（0.605?）<Zr⁴⁺（0.720?）,and the unit cell size gradually decreases.In addition,with the increase of Ti doping amount,the tolerance factor t increases.According to the law of tolerance factor,it can be seen that the antiferroelectricity weakens and the ferroelectricity increases,and the transition from the antiferroelectric phase to the ferroelectric phase appears,and the hysteresis loop gradually turns becomes square.Co-doping of La and Ti can significantly increase the breakdown electric field strength of the film（both greater than 3000 k V/cm,the film thickness is 500 nm）,and significantly increase the releasable energy storage density.When x=1.5%,the release energy storage density and storage energy storage density of the PLZT antiferroelectric film are significantly improved.The energy efficiency is the best,49.7 J/cm³ and 54%,respectively.The research shows that choosing an appropriate doping system is an effective way to improve the energy storage properties of PZO-based antiferroelectric thin films.