A series of energy storage technologies have been produced since the invention of pulse power system,among which capacitor energy storage technology has high energy storage density,low environmental pollution,and high reliability.Therefore,capacitor becomes the main component of pulse power system.Dielectric materials are the key for energy storage capacitor.Thin film dielectric materials have attracted much attention because of their small thickness and high dielectric breakdown strength,and their energy storage density can reach several times that of block ceramics.Bismuth sodium titanate(Bi0.5Na0.5TiO3)is relaxation ferroelectric with perovskite structure.The maximum polarization strength of Bi0.5Na0.5TiO3 thin film is large,but the dielectric breakdown strength is not high,resulting in its poor energy storage density.Strontium titanate(SrTiO3)is paraelectric with high dielectric breakdown strength but low dielectric constant,which leads to low energy storage density and limits its development in energy storage field.In this paper,Bi0.5Na0.5TiO3-SrTiO3 based thin films are taken as the research object.The high polarization of Bi0.5Na0.5TiO3 and the high breakdown strength of SrTiO3 were used to produce thin films with high energy storage density.(Bi0.5Na0.5)1-xSrxTiO3(x=0.2,0.3,0.4,0.5,0.6,0.7,abbreviated to BNT-ST100x)thin films were prepared by sol-gel method.It was found that strontium titanate could be dissolved with bismuth sodium titanate and form cubic perovskite structure.For sodium bismuth titanate,substitution of A bit ions can reduce the evaporation of Na,Bi element in the process of high temperature,thus reducing the content of oxygen vacancy and crystal defects,refining the grain size,reducing the ferroelectricity,improving the compactness of thin film,making its energy storage density improved.With the increase content of SrTiO3,the dielectric breakdown strength of BNT-ST thin film increases gradually,and the maximum electric field strength of BNT-ST70 is 1750kV/cm.Under the electric field intensity of 1500 kV/cm,the energy storage density of BNT-ST50 thin film reaches the maximum value of 32 J/cm3.A series of energy storage thin films were prepared by adding Mn in the optimal ratio of BNT-ST50 system.XRD analysis showed that Mn doping did not destroy the perovskite structure of BNT-ST50,and thin films were all cubic phase.The grain growth on the surface of thin films are in good condition.With the increase content of Mn,the grain size of BNT-ST50 thin film tends to decrease.This is because Mn ions replace the Ti ions position,which inhibits the valence change of Ti ions,thus reducing the number of oxygen vacancies and densifying the thin film structure.The maximum electric field strength of the undoped BNT-ST50 thin film is 1500 kV/cm.With the increase content of Mn,the maximum electric field strength was greatly improved to5000 kV/cm(Mn doping amount is 5 mol%,7 mol%,10 mol%).The maximum energy storage density of Mn-doped BNT-ST50 thin film is 80.7 J/cm3 when the Mn doping amount is 5 mol%,and its energy storage efficiency is 71%. |