Study On Microstructure And Electrical Properties Of BaTiO₃-BiMeO₃ Relaxor Ferroelectric Ceramics

Relaxor ferroelectric ceramics have advantages of high dielectric constant,wide temperature range,small temperature coefficient of capacitance,remarkable electrostrictive effect,fast response,etc.,and can be widely used in the manufacture of electronic component,such as multilayer ceramic capacitors,micro-displacement actuators,etc.Although the dielectric constant of barium titanate?BaTiO₃,short for BTO?is large dielectric constant,but the relaxation behavior is absence,and it shows poor temperature and frequency stability of dielectric properties,low Curie temperature,and low electrical breakdown strength,restricting the application and development of BTO ceramics.In view of the above deficiencies,this paper introduces bismuth-based perovskite ferroelectric materials such as BiYbO₃?BY?,BiAlO₃?BA?and BiFeO₃?BFO?with small tolerance factor and high Curie temperature into BTO to form a new type of BTO-based relaxor ferroelectric ceramics,respectively.Microwave sintering has has many advantages,such as high heating rate,short sintering time and low sintering temperature,which can effectively inhibit the volatilization of bismuth in the process of ceramic sintering,thereby reducing oxygen vacancy concentration and leakage current,and so improve the electrical properties of BTO-based relaxor ferroelectric ceramics.Therefore,the ferroelectric ceramics BTO-BiMeO₃?Me=Yb?Al?Fe?series were prepared by two different methods of conventional sintering and microwave sintering in this paper.The relationship between microstructure,electrical properties,BiMeO₃content and sintering method of ferroelectric ceramics were systematically studied.The obtained results are as follows:?1?The effects of BY single-component solid solution and sintering methods on the microstructure,electrical properties,relaxation behavior and energy storage properties of BTO ferroelectric ceramics were systematically investigated.The results show that the crystal structure of?1-x?BTO-x BY ceramics changes with BY content.When x?0.03,it is ferroelectric tetragonal phase.When x?0.06,it is pseudocubic phase.The smallest grain size is obtained at x=0.06;BY doping can improve the temperature and frequency stability of the dielectric properties of BTO ceramics,BTO ceramics change from normal ferroelectric ceramics to relaxor ferroelectric ceramics with increasing BY content,the relaxation behavior is significantly enhanced,the hysteresis loop becomes slimmer,the ferroelectricity is gradually weakened;the energy storage density is improved and the energy efficiency is significantly increased;the microwave sintering can increase the densities of the ceramics,inhibit the grain growth,and enhance the relaxation behavior,can reduce the leakage current,remnant polarization and coercive field,increase the difference between saturated polarization and remanent polarization,and thus increase the energy storage density and energy efficiency.?2?The effects of BA single-component solid solution and sintering methods on the microstructure,electrical properties,relaxation behavior and energy storage properties of BTO ferroelectric ceramics were systematically investigated.The results show that the crystal structures of?1-x?BTO-xBA ceramics change with BA content.When x?0.04,it is tetragonal phase.When x?0.08,it is pesudocubic phase.When0.04<x<0.08,it exists the tetragonal phase and the pesudocubic phase coexistence region,ie,the morphotropic phase boundary?MPB?;the introduction of BA can improve the density of the ceramic,and the proper content of BA helps to refine the grain.When x=0.04,the grain size is the smallest;the introduction of BA can significantly improve the temperature and frequency stability of dielectric properties of BTO ceramic;the introduction of BA can significantly perfect the ferroelectricity of BTO ceramics and enhance its energy storage characteristics.When x=0.08,the storage density is the largest,the energy efficiency is the highest at x=0.16;the microwave sintering is beneficial to further enhance the relaxation behavior of BTO-BY ceramics,and obtain smaller grain size and higher energy efficiency.?3?The effects of BFO single-component solid solution and sintering methods on the microstructure,electrical properties and magnetic properties of BTO ferroelectric ceramics were systematically investigated.The results indicate that the crystal structure of?1-x?BTO-xBFO ceramics changes with BY content.When x?0.65,it is rhombohedral phase.When x?0.7,it is pesudocubic phase.When 0.65<x<0.7,there may be a morphotropic phase boundary where rhombohedral phase and pesudocubic phase coexist;Introduction of BFO can obtain the smaller grains,proper amount of solid solution BFO can improve the densities of BTO ceramics,the largest density is obtained when x=0.7;Introduction of BFO can also significantly improve ferroelectricity and enhance the magnetic properties of BTO ceramics;microwave sintering can inhibit grain growth,Compared with the conventional sintering,the grain sizes of the microwave sintered ceramics are samller and more uniform,and their ferroelectricity and magnetic properties deteriorate.?4?The effects of BFO solid solution and sintering methods on the microstructure and electrical properties of BTO-BY ferroelectric ceramics were systematically investigated.The results show that the proper amount of solid solution BFO can enhance the densification of BTO-BY ferroelectric ceramics.With the increase of BFO content,the grain size of?0.95-x?BTO-0.05BY-xBFO ceramics increases first,then decreases and then increases.the maximum is obtained when x=0.01 and the smallest is obtained at x=0.02;the proper amount of solid solution BFO can improve the temperature and frequency stability of BTO-BY ceramics,enhance the relaxation behavior of BTO-BY ceramics.The dielectric constant,remanent polarization and coercive electric field of BTO-BY ceramics decrease first and then increase with the increase of BFO solid solution.When x=0.01,it is the smallest,which is related to the defects such as oxygen vacancies caused by BFO doping and the compactness of the microstructure induced by Bi₂O₃ sintering aid;The grain size,ferroelectricity,energy storage density and energy efficiency of microwave sintering ceramics are all smaller than those of the conventional sintered samples for the same composition.?5?The effects of BA solid solution and sintering methods on the microstructure and electrical properties of BTO-BY ferroelectric ceramics were systematically investigated.The results show that:?0.9-x?BTO-0.1BY-xBA ceramic crystal structure changes with BA content.When x<0.02,it is tetragonal phase.When x>0.02,it is trigonal phase.When x=0.02,there exists a morphotropic phase boundary where the trigonal phase and the tetragonal phase coexist.With the increase of BA content,the dielectric constant of?0.9-x?BTO-0.1BY-xBA ceramics decreases first and then increases,the dielectric loss increases first and then decreases.The spontaneous polarization,remanent polarization and coercive electric field increase first and then decrease with the increase of BA.The spontaneous polarization,energy storage density and energy efficiency of microwave sintered samples are much higher than those of conventional sintered samples,the remanent polarization and coercive electric field are stronger than those of the conventional sintered samples.When x=0.02,the spontaneous polarization,remanent polarization and coercive electric field of the microwave sintered samples are the highest,they are 20.95?C/cm²,3.70?C/cm²,5.86 kV/cm,respectively.BTO-BY ceramics have a maximum energy storage density of 0.86 J/cm³ and an energy efficiency of 97.44%.