The Studies On The Energy Storage Properties For The NBT-BFO-based Films

Dielectric capacitors,which store electric energy in the form of electrostatic field via dielectric polarization,are widely used in the pulse power electronic equipment due to their high power density and ultrashort discharge time.The development of electronic devices towards miniaturization nowadays is urgent to increase the energy density and storage efficiency of dielectric materials.Dielectric ceramic films have shown the optimal energy storage properties among the different dielectric materials studied,including polymers,glasses,and both bulk and film-based ceramics.In ceramic materials,relaxor ferroelectrics have better energy storage properties than normal ferroelectrics.Bismuth sodium titanate(Na_0.5Bi_0.5TiO₃)is one kind of relaxor ferroelectrics,and based on the previous studies,both doping BiFeO₃ and La³⁺are beneficial to improve its energy storage properties.In this paper,BiFeO₃ and La³⁺were co-doped to further improve the energy storage properties of Na_0.5Bi_0.5TiO₃-based films,i.e.,the studies on the energy storage properties for the BiFeO₃-doped Na_0.5Bi_0.5TiO₃ films and further the energy storage properties for the La³⁺-doped0.9Na_0.5Bi_0.5TiO₃-0.1BiFeO₃ films were conducted.The studies on the energy storage properties of the?1-x?Na_0.5Bi_0.5TiO₃-xBiFeO₃solid solution films:In this work,the cost effective sol-gel method was used to prepare lead-free?1-x?Na_0.5Bi_0.5TiO₃-xBiFeO₃?x=0.00,0.05,0.10,0.15?single-phase perovskite films.For BiFeO₃-doped Na_0.5Bi_0.5TiO₃ films,Fe³⁺is expected to replace the Ti⁴⁺at the B-site of the perovskite lattice.Appropriate doping content can increase the density of the films,and decrease the carrier concentration to reduce the leakage current density and dielectric loss,improving the breakdown strength of the films.In addition,replacing Ti⁴⁺with Fe³⁺properly can reduce the films defects to promote the polarization behavior,thereby increasing the dielectric constant of the films.Moreover,properly doping BiFeO₃ can lead to the distortion of TiO₆ octahedron and weaken the pinning effect of domain wall,so as to improve the ferroelectric properties of the films.Consequently,in this system,for the 0.90Na_0.5Bi_0.5TiO₃-0.10BiFeO₃ film at the electric field of 1414kV/cm,the value of P_max-P_r reaches 88.1?C/cm²,obtaining the optimal energy storage properties that the energy storage density is 36.1J/cm³ and the efficiency is 56.8%,possessing high thermal stability over the wide range of temperatures?0?⁸0??under the electric field of 1414kV/cm.Based on the above studies,the energy storage properties of the0.90Na_0.5Bi_0.5TiO₃-0.10BiFeO₃ film reached the optimal level,and then doping it with La³⁺was carried out,i.e.,the energy storage properties of 0.9Na_0.5Bi_0.5TiO₃-0.1BiFeO₃-xLa films were studied.In this work,the lead-free 0.9Na_0.5Bi_0.5TiO₃-0.1BiFeO₃-xLa?x=0.000,0.023,0.045,0.068 and 0.090?single-phase perovskite films were also prepared by sol-gel method.Appropriate substitution of La³⁺for A-site in crystal lattice will increase the density of the films,facilitate the polarization of the films,and create the polar nano regions?PNRs?in the original matrix,further resulting in the stronger relaxor properties and lower P_r.Simultaneously,doping the right amount of La³⁺in the materials can lead to the distortion of the oxygen octahedron in the lattice to increase P_max,and inhibit the carrier concentration to enhance the breakdown strength.Among all the prepared films,the 0.9Na_0.5Bi_0.5TiO₃-0.1BiFeO₃ film doped with 0.068mol La³⁺exhibits the higher energy storage density?52.4J/cm³?and the considerable energy storage efficiency?60.3%?under the electric field of 2700kV/cm at room temperature,possessing high thermal stability over the wide range of temperatures?-60?⁸0??under the electric field of 1500kV/cm,which indicate that the 0.9Na_0.5Bi_0.5TiO₃-0.1BiFeO₃-0.068La film may be a promising lead-free material for energy storage application.