| Dielectric capacitors are widely used in the pulsed-power systems of auto and aviation industry,medical facility,and military weapons due to their large power density,fast discharge speed,as well as remarkable temperature and frequency stabilities.However,the low energy storage density of dielectric capacitors severely limits their practical applications.Furthermore,with the multifaceted development of industry,there are more requirements for dielectric capacitors to work well in high temperature.For example,the electronics around the engine of cars are required to work well above 150℃,the electronics in oil exploration need to withstand 200～300℃,but many dielectric ceramic capacitors cannot meet the requirements of operation in harsh environments.Therefore,exploring dielectric ceramic capacitors with high energy storage density and excellent thermal-stable dielectric properties has become an inevitable upward trend.Among dielectric ceramic capacitors,relaxor ferroelectrics are considered as promising candidates for dielectric energy storage materials because of small size polar nanoregions(PNRs),slender P-E loops and temperature-insensitive permittivity.(Bi0.5Na0.5)TiO3(BNTbased)ceramics,one of the typical relaxor ferroelectrics,have attracted wide attention owing to their high maximum polarization(Pm)and high dielectric constant(εr).However,the large remnant polarization Pr and coercive field Ec are not conducive to the improvement of energy storage performances.Therefore,in this paper,BNT was selected as the matrix,and then constructing solid solutions by ion doping in A/B site for decreasing Pr and Ec,so as to improve the energy storage performances and dielectric constant temperature stability of BNT ceramics.Research contents specifically as follows:(1)(1-x)(Bi0.5Na0.5)TiO3-xBa(Al0.5Ta0.5)O3(BNT-100xBAT)ceramics were prepared by traditional solid-state reaction method,and the phase structure,microstructure,dielectric,ferroelectric and domain properties were characterized in detail.The results show that all the samples show a pure perovskite structure without secondary phase.As BAT content increases,there is a phase transition from Rhombohedral(R3c)to Tetragonal(P4bm).The coupling of P4bm PNRs is weak over a wide temperature range,which is conducive to improving thermlstable dielectric.Therefore,BNT-10BAT obtain a high εr=2770±15%in a wide temperature range of 67～345 ℃.Furthermore,PFM phase diagrams show that BNT-10BAT ceramics exhibit fast response to electric field,which is beneficial to decreasing Pr and Ec.And Ta2O5 with a wide band gap incorporates into BNT-based ceramics is good to improve the breakdown strength.Therefore,a large energy storage density(W)of 3.28 J/cm3,a large recoverable energy storage density(Wrec)of 2.42 J/cm3 and high energy storage efficiency(η)of 73.7%are achieved in x=0.10.At the same time,BNT-10BAT ceramics show remarkable temperature(30～150℃)and frequency(0.1-10 Hz)stabilities.(2)Compared with undoped BNT ceramics,the energy storage density of BNT-10BAT is improved,but the Wrec is still low(<3 J/cm3),Therefore,(1-x)(Bi0.5Na0.5)TiO3-xSr(Al0.5T0.5)O3(BNT-100xSAT)ceramic samples were prepared by the traditional solid state reaction method,and the phase structure and electrical properties were characterized in details.The PFM phase diagrams show that the addition of SAT break the long-range order,inducing the generation of PNRs,which is sensitive to the external electric field.Therefore,the Pr is significantly reduced,and an excellent Wrec of 3.54 J/cm3 and a large η of 83.1%,accompanied with temperature(30～170℃)and frequency(0.1～10Hz)stabilities,and fast discharge speed are obtained in BNT-13SAT.Besides,BNT-13SAT ceramics obtain a high εr=2171±15%in a wide temperature range of 42～319℃,indicating that this system possesses great potential in high temperature ceramic capacitors.(3)According to the electronic Industry Association(EIA)standards,the operation temperature of Z9R capacitors is 10～200℃.(1-x)(Bi0.5Na0.5)TiO3-xCa(Al0.5Ta0.5)O3(BNT100xCAT)ceramics were prepared by traditional solid phase reaction method,and the crystal structure,microstructure,dielectric properties and ferroelectric properties were characterized in detail.The small radius of Ca2+ with low relative atomic mass is conducive to inducing relaxation properties,which is good for improving thermal-stable dielectric.Therefore,an excellent temperature stability of dielectric(-25～358℃)is achieved in x=0.08,fulfilling the industry standard of Z9R specification.Furthermore,BNT-08CAT ceramics achieve an excellent Wrec of 3.95 J/cm3,a large η of 76.4%and remarkable temperature and frequency stabilites.In addition,BNT-08CAT ceramics exhibit ultra-fast discharge speed(τ0.9～78 ns).The above characteristics indicate that the system has great potential in the applications of high temperature dielectric capacitors and pulse power systems.In conclusion,this paper achieves excellent energy storage performances and thermalstable dielectric through a series of composition regulation,which provides potential candidate materials for high-temperature dielectric ceramic capacitors. |
