| Pulsed power system is a technology that arose in the 1930s and widely used in defence,scientific research,environmental protection,medical devices and mobile electronics.Capacitors,as the core part of pulsed power system,require high energy storage density,small size,light weight,low cost and high reliability.Among them,ceramic capacitors with merits of high power density,good high frequency characteristics,high voltage withstand and low loss are particularly suitable for capacitor chip,but the small energy storage density of ceramic capacitors has limited their application.The results of previous studies by our group show that(Bi0.5Na0.5)0.65(Ba0.3Sr0.7)0.35Ti O3（BNBST）ceramics have a high maximum polarization Pmax（～50μC/cm~2）and a low remnant polarization Pr（～13μC/cm~2）at room temperature,making them promising for dielectric energy materials.To further enhance the energy storage properties of BNBST,this thesis investigates the effects of different complex ions(Mg1/2W1/2)4+,(Zn1/3Ta2/3)4+and(Mg1/3Ta2/3)4+on the phase structure,microscopic morphology and dielectric and ferroelectric properties of BNBST ceramics.The specific studies are as follows.Firstly,the effect of B-site(Mg1/2W1/2)4+complex ion doping on the phase structure,microscopic morphology and electrical properties of BNBST-x MW（x=0.01,0.02,0.03,0.04,0.05,0.06）ceramics were investigated.The formation of Ba WO4 significantly deteriorates the electrical properties of the samples,leading to a reduction in energy storage density.In addition,the analysis of the microscopic morphology of the samples revealed that inappropriate thermal corrosion temperatures can produce unusually large Ti O2growth on the surface of the samples.The energy storage density of BNBST-x MW ceramics at 80 k V/cm was 0.934 J/cm~3 at x=0.01,with an energy storage efficiency of67.5%,an improvement of only 10%over the undoped counterpart.Secondly,the effect of B-site(Zn1/3Ta2/3)4+composite ion doping on the phase structure,microscopic morphology,temperature stability,fatigue stability and dielectric and ferroelectric properties of BNBST-x ZT（x=0.01,0.02,0.03,0.04,0.05,0.06）ceramics were investigated.The results show that the addition of(Zn1/3Ta2/3)4+complex ions has no significant effect on the phase structure of BNBST-x ZT ceramics,but can effectively improve the relaxation characteristics and reduce the Pr,which makes the P-E loops more“slim”,and the Curie peak of BNBST-x ZT ceramics shift to low temperature and broadened.With the increase in doping from x=0 to x=0.06,the Curie temperature drops from 92.5°C to 10.9°C,which facilitates the application of the material at room temperature.The BNBST-0.04ZT ceramic has an energy density Wrec=1.06 J/cm~3 and an energy efficiencyη=79%at E=80k V/cm.At the same time,BNBST-0.04ZT possesses good temperature stability and fatigue resistance at 60 k V/cm,20-160°C and 10~4 cycles.Finally,the effect of B-site(Mg1/3Ta2/3)4+complex ion doping on the phase structure,microscopic morphology,electric breakdown strength,temperature stability,fatigue stability and dielectric and ferroelectric properties of BNBST-x MT（x=0.01,0.02,0.03,0.04,0.05,0.06）ceramics were investigated.Similar to the(Zn1/3Ta2/3)4+complex ions,the(Mg1/3Ta2/3)4+complex ions has no significant effect on the phase structure,but can effectively improve the relaxation characteristics and reduce Pr,which makes the P-E loops are more“slim”,and the Curie peak of BNBST-x MT ceramics shifts to lower temperatures and broadened.Under an electric field of E=125 k V/cm,the BNBST-0.04MT ceramic has an energy density of Wrec=1.69 J/cm~3 and an energy efficiency ofη=80%.The increase in breakdown strength compared to the undoped sample is attributed to the high bandgap of Ta2O5and the ability of Ta5+to effectively reduce oxygen vacancies and lower leakage currents.The BNBST-0.04MT also exhibits good temperature stability,frequency stability and fatigue resistance at 60 k V/cm,20-160°C,1-100 Hz and 10~4 cycles. |
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