| Dielectric capacitors store energy in the form of electric field.Dielectric capacitors have the advantages of high power-density,fast charge-discharge rate and good fatigue resistance,and play an important role in the fields of pulse power system and power system.The dielectric material is the key to determine the energy storage capacity of pulse capacitors.Ba Ti O3 ceramic dielectric materials have the characteristics of large dielectric constant,low dielectric loss and good insulation,which have a wide application prospect in dielectric,ferroelectric and piezoelectric fields.However,its development and application as a dielectric energy storage material are limited by its relatively large residual polarization strength and poor dielectric temperature stability.In this thesis,the Ba Ti O3(BT)material was introduced by Bi(Mg1/2Zr1/2)O3(BMZ)to form BT-based relaxor ferroelectrics,which improved the residual polarization strength,enhanced the dielectric temperature stability and increased the electric field strength.The effect of composition and phase structure on the electrical properties of BT ceramics was investigated,and the synergistic enhancement of dielectric properties and energy storage properties of BT-BMZ ceramics was realized.In addition,BT-BMZ thin films were prepared by sol-gel method based on the trend of integration,miniaturization,lightweight and flexibility of capacitors.The effects of composition design and thickness regulation on dielectric properties of BT-BMZ films were investigated.Amorphous films were prepared by reducing annealing temperature,a new idea of forming co-existing microstructure of nano-crystalline in amorphous film is put forward,which can improve the breakdown field strength,polarization strength and dielectric storage properties of BT-BMZ material.In addition,BT-BMZ thin films were prepared by sol-gel method based on the trend of integration,miniaturization,lightweight and flexibility of adaptive devices.The effects of composition design and thickness regulation on dielectric properties and energy storage properties of BT-BMZ thin films were investigated.A new idea of forming co-existing microstructure of nanocrystals in amorphous thin film according to regulate the heat treatment process was put forward,which can improve the electric field strength,polarization strength to achieve the overall enhancement of energy storage properties of BT-BMZ material.The details are as follows:(1)The(1-x)BT-x BMZ ceramic materials were designed and prepared.The introduction of BMZ was destroyed the long-range ordered ferroelectric tetragonal phase structure of BT,led to the appearance of polar nanoscale region and induced dielectric relaxation behavior.The temperature stability was enhanced effectively because of the dispersion phase transition.When x = 0.20,the change of capacitancetemperature(TCC25℃)was less than ±15% in the range of-40 oC~260 oC,which showed excellent dielectric temperature stability.Meanwhile,the addition of BMZ was decreased residual polarization strength,increased the electric field strength and improved the energy storage properties of BT.The discharge energy storage densities of the material were 1.04 ~ 1.45 J/cm3 at 0.08 ≤ x ≤ 0.20,and the energy efficiencies were more than 90% in the range of 0.10 ≤ x ≤ 0.20.The 0.85BT-0.15 BMZ ceramics possessed excellent energy storage thermal stability in the range from 25 oC to 150 oC,and ultra-fast pulse discharge time with 1.3 μs.In addition,0.9BT-0.1BMZ ceramics were prepared by sol-gel method to reduce the average grain size to sub-micron.The finite element simulation was revealed that the decrease of grain size made the grain boundary bear more electric field.The critical electric field strength was significantly increased to 325 k V/cm,the discharge energy storage density was reached to 2.0 J/cm3,so the energy storage properties of BT-BMZ ceramics were further improved.(2)The(1-x)BT-x BMZ thin films were designed and fabricated.The precursor solutions of(1-x)BT-x BMZ were successfully prepared by sol-gel method,and the thin films were grown on conductive substrates by rapid thermal treatment.The effects of substrate materials on phase structure and energy storage properties of BT-BMZ thin films were investigated.Compared with BT-BMZ ceramics,the grain size and thickness of BT-BMZ thin films were greatly reduced to nanometer scale.This small size effect not only increased the resistivity of the thin films,but also reduced the electric breakdown paths,so the electric field strength of BT-BMZ thin films was greatly enhanced.By optimizing the composition and adjusting the thickness,when x = 0.08 and the thickness was about 175 nm,the optimal discharge energy storage density was ~ 18.2 J/cm3(Emax ~ 1430 k V/cm,Pmax ~ 38.3 μC/cm2),which was much higher than that of BT-BMZ ceramics,but its energy storage efficiency(~ 60.9%)was relatively low.(3)The 0.92BT-0.08 BMZ composite thin films coexisting with amorphous and nanocrystals were built.The high insulation of amorphous thin films was used to further improve the electric field strength,and the polarization strength were matained by controlling the content of nanocrystal,so the energy storage properties of 0.92BT-0.08 BMZ composite thin films can be optimized further.The effects of annealing temperatures and holding times on the dielectric properties and energy storage properties of 0.92BT-0.08 BMZ composite thin films were investigated.When the annealing temperature was 600 oC and the holding temperature was 8 min,the discharge energy density of 0.92BT-0.08 BMZ amorphous films was enhanced to 58.4 J/cm3 at high critical electric field strength(~3600 k V/cm).It also had a good energy storage efficiency(~ 82.7%),which showed excellent energy storage properties.Based on this strategy,a new type of high performance lead-free dielectric energy storage thin film material was successfully obtained,which also provided an effective way to improve the energy storage properties of Ba Ti O3-based materials. |
PDF Full Text Request