BiFeO₃-based Complex-phase Ceramic Iron Polarization Control And Energy Storage Application Research

Although the dielectric capacitor has fast charge and discharge speed and good stability,its energy storage density is relatively small,which leads to limited applications in energy storage.Therefore,the preparation of a high energy storage density dielectric capacitor has attracted the attention of researchers.Bismuth ferrite?Bi Fe O₃?is an ABO₃ type perovskite multiferroic material with high spontaneous polarization in theory,but Bi Fe O₃ has two main disadvantages: First,during the sintering process,the volatilization of Bi2O₃ leads to oxygen vacancies inside Bi Fe O₃ the concentration increases;secondly,because the formation energy of Bi Fe O₃ is small,it is not easy to synthesize,so the application of Bi Fe O₃ ceramics in energy storage is limited.In response to the above two problems,this paper uses doping modification to adjust the polarization behavior of Bi Fe O₃ to increase its saturation polarization strength,and secondly to add nano-Ba Ti O₃ in Bi Fe O₃ to increase its energy storage density.Using first-principles calculations,the electronic structure and energy storage mechanism of Bi Fe O₃ and Ba Ti O₃ are analyzed.Adding Nd³⁺/Sm³⁺ ions to the A site of Bi Fe O₃ and adding Ru4+ ions to the B site,the polarization behavior of Bi Fe O₃ is optimized by changing the content of Sm³⁺ ions.The results show that the grain size and polarization intensity value increase with the content of Sm³⁺ ions and gradually decrease,when the Sm³⁺ ion content is 2mol%,the saturation polarization value Pmax is 66?C/cm2.Adding nano-Ba Ti O₃ to Bi_0.88Nd_0.1Sm_0.02 Fe O₃ to prepare?1-x?Bi_0.88Nd_0.1Sm_0.02 Fe O₃-x Ba Ti O₃ ceramics,and studying the energy storage behavior of ceramics by changing the content of nano-Ba Ti O₃.The results show that the ceramic has ferroelectricity at room temperature,and when the content of nano-Ba Ti O₃ is 50 mol %,the effective energy storage density Wrec and energy storage efficiency ? measured by the ceramic when the electric field strength is 210 k V/cm are maximum.At this time,the Wrec value is 3.24 J/cm³ and the ? value is 85.2%.In order to further improve the energy storage characteristics,this component of ceramics is quenched at different temperatures?600 ?C,700 ?C,800 ?C?,and its energy storage density and energy storage efficiency is calculated and obtained through analysis,When the quenching temperature is 700?C,the energy storage characteristic is the best,the effective energy storage density Wrec can reach 3.65 J/cm³ when the electric field strength is about 220 k V/cm,which proves that the proper quenching temperature will indeed increase the ceramic energy storage density.The first-principles calculation method was used to analyze the structure of Bi Fe O₃ and Ba Ti O₃.The results show that the forbidden band width of Bi Fe O₃ is E_g = 1.023 e V and the formation energy is-0.132 e V,which proves that Bi Fe O₃ is easily decomposed during sintering;the forbidden band width of Ba Ti O₃ is E_g = 1.848 e V and the formation energy is-1.543 e V;Through the linear superposition method,it is simulated that with the increase of nano-Ba Ti O₃ content,the lattice constant of?1-x?Bi_0.88Nd_0.1Sm_0.02 Fe O₃-x Ba Ti O₃ ceramic gradually decreases,which is the same as the XRD result.It is calculated that when the content of nano-Ba Ti O₃ is 50 mol%,according to E?0.5 Bi Fe O₃-0.5 Ba Ti O₃?-E?Bi Fe O₃?-E?Ba Ti O₃?<0,it is proved that under this composition,the core-shell structure is more likely to form than the solid solution It is proved from the side that the core-shell structure can indeed increase the energy storage density of the material.