Influence Of A-site Nonstiochiometry On The Structure And Electrical Properties Of Sodium Bismuth Titanate-based Ferroelectric Thin Films

In recent years,with the continuous consumption of non-renewable resources such as fossil fuels,the energy crisis has become increasingly prominent,and people are paying more and more attention to energy storage materials.There are usually four kinds dielectric materials:ferroelectric materials,anti-ferroelectric materials,relaxation ferroelectrics and linear dielectric materials.Ferroelectric materials have been received lots of researches,especially for the BNT(Bi_0.5Na_0.5Ti O₃)-based ferroelectric thin films,because of its good ferroelectric performances at room temperature?2P_r=76?C/cm²,T_c=320°C?.However,during the high temperature annealing process,Bi and Na are easy to volatilize,and the film's leakage current will be more,badly to the energy storage density.In this paper,the influence of nonstoichiometric ratio of A-site element on the microstructure and electrical properties of all the BNT-based thin films were studied systematically.Bi_0.5?1+x?Na_0.5?1+y??x,y=0,±5%,+10%?and BNT_?1-x?Mn_x?x=0,1%,2%,3%?were prepared on a Pt/Ti/Si O₂/Si substrate by the CSD?Chemical Solution Deposition?method,in this paper.The phase purity and crystal structure were examined by X-ray diffraction.The surface sectional morphologies of thin films were observed by FESEM?Field Emission Scaling Electronic Microscopy?.Ferroelectric properties were evaluated using the Precision work-station ferroelectric measurement system.With the help of impedance analyzer,the I-V curves of the samples was measured.The research content of this article is mainly including the following two aspects:1.Bi_0.5?1+x?Na_0.5?1+y??x,y=0,±5%,+10%?thin films were prepared,and the test results show that when Na is insufficiently,a visible impurity phase?pyrochlore phase?will be formed,while when Bi is insufficient,no visible second phase will be produced,indicating that the amount of Na has more influence on the BNT films than the Bi.When overdoping 10%of Bi and 5%of Na,the BNT film has the smallest leakage current density,the highest energy storage density?13.05 J/cm³?,the largest energy storage efficiency?52%?.2.BNT_?1-x?Mn_x?x=0,1%,2%,3%?thin films were prepared based the above study,and the following conclusions are obtained through exploration:Mn was doped at B-site,which can effectively suppress the generation of oxygen vacancies,and also reduce the leakage current and increase the BDS?Breakdown Strength?.When the Mn doping amount is 0.02 mol,the leakage is the smallest(10^-11A/cm²)and the BDS is the largest?2453.3 k V/cm?.Through calculating the energy storage density of these films,when the Mn doping amount is 0.02 mol,the energy storage density is the highest?30.75 J/cm³?,and the energy storage efficiency is 57%.