| Dielectric capacitors are widely applied as energy-storage devices in pulsed power equipments due to their high power density,fast charge-discharge rate,wide range of working temperature and long cycle life.BST-based ceramic materials can not meet the requirements of practical applications because of low energy-storage density and high energy-storage density only at high electric field.Thus,it has to face the big problem of manufacture and application in the trend of miniaturization,integration and low energy consumption of electronic devices.Bi0.5Na0.5Ti O3-based relaxor ferroelectrics,which possess high polarization and a high energy-storage density can be achieved after modification,become a new research hotspot in the field of energy-storage dielectric materials.In this paper,BCTZ,Sn O2 and MgO were doped into BNT to decrease its remanent polarization and coercive electric field and enhance its dielectric breakdown strength and improve its energy-storage density.The crystal structures,micro morphologies,dielectric,ferroelectric and energy-storage properties of these materials were systematically studied.?1-x?BNT-xBCTZ ceramics were prepared by solid state method.XRD results reveal that the cell volume of the samples gradually increase with the increasing content of BCTZ and all samples exhibit a preudo-cubic symmetry.When x?0.4,all samples have two dielectric peaks due to the existence of two types of PNRs?low-temperature PNRs and high-temperature PNRs?.The first anomaly,occurring at lower temperatures and showing frequency dispersion.The second anomaly appears at higher temperatures shows a broad peak,without frequency dispersion.The magnitude of permittivity of second anomaly decreases rapidly and the position of second anomaly gradually shifts to low temperature with the increasing content of BCTZ.When 0.2?x?0.4,the samples show a pinched P-E hysteresis loops and the remanent polarization decreases significantly,while the maximum polarization almost unchanged.Solid state route was used to prepare 0.55BNT-0.45Ba0.85Ca0.15Ti0.9-xZr0.1-SnxO3 ceramics,all samples exhibit a preudo-cubic structure.The phase transition temperature and permittivity of the samples gradually decrease with the increasing content of Sn4+.When x?0.02,the samples show a pinched P-E hysteresis loop.As the content of Sn4+ continues increasing,the samples exhibit a slim P-E hysteresis loop and the maximum and remanent polarization gradually decrease.Furthermore,the polarization current peaks related to the reversible phase transition between non-ferroelectric and ferroelectric phase gradually disappear.The slope of P-E hysteresis loop and energy loss were decreased and the dielectric breakdown strength was enhanced by the addition of Sn4+.When x=0.05,the sample has a high dielectric breakdown strength of 13.02 k V·mm-1,a high maximum polarization of 30.58 ?C·cm-2,and a high energy efficiency of 72.08 %,making it possesses a high energy-storage density of 1.21 J/cm3.0.55BNT-0.45BCTZS-x wt% Mg O ceramics were prepared by solid state route,all samples have perovskite crystal structure.MgO-doped samples posses secondary phases of MgO and Mg2TiO4.The distribution of MgO is inhomogeneous and it mainly accumulate at the grain boundaries.0.55BNT-0.45 BCTZS sample shows obvious frequency dispersion,The MgO-doped samples show a diffuse phase transition characteristic,however,without the frequency shift of Tm typical of relaxor ferroelectrics.The dielectric peaks become broader and the magnitude of permittivity gradually decreases with the increasing content of MgO.Dielectric breakdown strength of 0.55BNT-0.45 BCTZS can be effectively enhanced by the introduction of MgO and the x=0.07 sample exhibits a high dielectric breakdown strength of 19.41 k V·mm-1?0.55BNT-0.45BCTZS-5 wt% Mg O sample exhibits a high dielectric breakdown strength of 18.97 kV·mm-1,a high maximum polarization of 23.57 ?C·cm-2 and a high energy efficiency of 79.51 %,making it has a high energy-storage density of 1.62 J·cm-3?0.55BNT-0.45BCTZS-x wt% Mg O ceramics were sintered by microwave sintering.The chemical reaction between MgO and the matrix was inhibited by microwave sintering,The distribution of MgO is inhomogeneous and it mainly accumulate at the grain boundaries.The MgO-doped samples prepared by microwave sintering have a higher permittivity than that prepared by traditional sintering.Compared to the samples prepared by traditional sintering,the samples prepared by microwave sintering show a higher maximum polarization,while the dielectric breakdown strength almost unchanged.0.55BNT-0.45BCTZS-5 wt% MgO sample exhibits a high dielectric breakdown strength of 18.97 k V·mm-1,a high maximum polarization of 30.53 ?C·cm-2 and a high energy efficiency of 79.51 %,making it has a high energy-storage density of 2.09 J·cm-3. |
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