Structure Regulation And Properties Analysis Of Na_0.5Bi_0.5TiO₃-BaTiO₃ Based Relaxor Ferroelectric Ceramics

With the rapid development of electronic circuit integration and high-end intelligent manufacturing,Multi-layer Ceramic Capacitors（MLCCs）,known as the"rice of the electronic industry",has also ushered in a climax of development,with the market size reaching 63 billion yuan in 2021.Dielectric ceramics are the core of MLCCs,which determine the energy storage performance.However,most energy storage ceramics have low energy storage density.The development of dielectric ceramics with high energy storage density is the basis for the miniaturization and integration of MLCCs.The ceramics of current commercial MLCCs contain a lot of lead,which damages the natural environment and human health.Finding suitable lead-free dielectric ceramics with high energy storage density has become a hotspot of current research.Bismuth in bismuth sodium titanate(Na_0.5Bi_0.5Ti O₃)has similar electronic structure to lead and is considered as a good substitute for lead-based ceramics.Barium titanate（Ba Ti O₃）is a well-studied ceramic system with excellent dielectric and ferroelectric properties.The combination bismuth sodium titanate-barium titanate（NBT-BT）has high polarization and strong ferroelectric properties.Therefore,this paper developes a series of energy storage ceramics based on NBT-BT,and obtains lead-free dielectric ceramics with good energy storage performance by means of structure regulation,element doping,process improvement and other means,so as to provide a reference scheme for improving the energy storage performance.A series of（1-x）NBT-x BT ceramics were prepared by introducing BT into NBT to form a relaxor ferroelectric solid solution with high polarization.Through the analysis of dielectric and ferroelectric properties,the 0.94NBT-0.06BT ceramics which are most beneficial to energy storage are selected as the matrix for subsequent research.It is further doped and improved to obtain lead-free energy storage ceramics with high energy storage density.With the introduction of K_0.5Na_0.5Nb O₃（KNN）ferroelectric dielectric ceramics to NBT-BT,K⁺and Nb⁵⁺occupy the A and B-site of perovskite,respectively,forming perovskite-type solid solution.KNN destroys the long-range ordered structure of the matrix and further improves its relaxation characteristics.The higherΔZ value of Nb⁵⁺improves the saturation polarization of the ceramics,and the addition of KNN refines the grain size of the matrix which effectively improves the electric field strength of the ceramics.The 0.9NBT-BT-0.1KNN ceramic sample has an energy storage density of 2.81J/cm³ under 180 k V/cm,which greatly improves the energy storage performance of the matrix.However,the domains of matrix and KNN are macrodomain structures with large residual polarization and coercive field,which cannot meet the requirements of high efficiency.Therefore,introduce SBT and lanthanide elements into NBT-BT to break the macrodomain structure and effectively reduce the residual polarization and coercivity field,leading theΔP of NBT-BT-0.4SBT-Dy up to 41.3μC/cm².And combined with viscosity polymer processing（VPP）to prepare more uniform and dense ceramics,increased the electric field intensity of ceramic from 150 k V/cm to 270 k V/cm,and improving the energy storage density of ceramic up to 4.87 J/cm³.At the same time,a micro-domain relaxation ferroelectric ceramic system with weak pin effect was constructed,and the NBT-BT-25CT lead-free ceramics were designed and fabricated.The ultra-high energy storage density of 6.62 J/cm³ was obtained at 520 k V/cm,and the energy storage efficiency was over 80%.After 10⁶ cycles under 200 k V/cm electric field,the energy storage efficiency still remains at 85.9%,and the change rate of energy storage density of ceramic is only 4%,which has good fatigue resistance.In conclusion,the series of energy storage ceramics developed based on bismuth sodium titanate-barium titanate（NBT-BT）show good energy storage performance.The optimized strategy of doping different dielectrics and combining elements can effectively regulate the microstructure of ceramics,and greatly improve the energy storage performance of ceramics by means of process improvement,which can provide theoretical basis for the development of new lead-free dielectric energy storage ceramics.