| Dielectric capacitors have the characteristics of high power density,fast charging and discharging speed,and good temperature stability.They are widely used in new energy vehicles,oil exploration,aerospace and other fields,and are key components of power electronics and pulse power technology.With the continuous development of sustainable energy and pulse power technology,the requirements for the energy storage characteristics and temperature stability of dielectric capacitors are getting higher and higher.Traditional ceramic capacitors work below 150℃,which cannot meet their application requirements.In this paper,0.94Na0.5Bi0.5TiO30.06BaTiO3(BNT-BT)is used as the research object.Taking advantage of its high saturation polarization strength and dual dielectric peaks,dielectric materials with good energy storage characteristics and temperature stability can be obtained by component doping to induce relaxation,rare earth doping to reduce oxygen vacancy content,adding oxides with high breakdown field strength and optimizing the preparation process.At the same time,the physical mechanism that affect the temperature stability of its energy storage properties and dielectric properties was explored.The main contents of the thesis include the following aspects:The ternary system(0.94-x)Na0.5Bi0.5TiO3-xSrNb2O6-0.06BaTiO3(abbreviated as BNT100xSNO-6BT)ferroelectric ceramics were prepared by the conventional solid-state reaction method.The effects of doping SrNb2O6(SNO)on the phase structure,dielectric properties,energy storage properties and electrical conductivity of the material matrix were systematically studied and related physics was revealed.The results indicate that all samples exhibit a pseudo-cubic perovskite structure.When the doping amount of SrNb2O6 exceeds 0.05,a second phase Bi2Ti2O7 is produced.The introduction of SNO leads to the transformation of long-range ordered ferroelectric domains into randomly oriented polar nanoregions(PNRs),and the weakening of the coupling effect between oxygen octahedra broadens the coexistence temperature range of tripartite and tetragonal PNRs;finally,the improvement of ceramic dielectric properties and energy storage performance temperature stability was achieved.Among them,the sample with a doping amount of x=0.03 exhibits the best dielectric temperature stability in the wide temperature range of 27℃ to 402℃(△ε’/ε’150℃±15%),and has a relatively high permittivity(2092)at 150℃.In addition,under a low electric field intensity of 80 kV/cm,the energy storage density and energy storage efficiency of the sample are 0.96 J/cm3 and 52.8%,respectively.BNT100xSNO-6BT ceramics have good application prospects in high-temperature dielectric capacitors with operating temperatures far exceeding 150℃.Using BNT-3SNO-6BT as the matrix and adding different amounts of Pr2O3,0.91Na0.5Bi0.5TiO3-0.3SrNb2O6-0.06BaTiO3-xPr2O3(abbreviated as BNT-3SNO-6BT:x Pr)ceramics were prepared by traditional solid-state reaction method.The phase structure,electrical properties,and upconversion optical properties of the materials were studied.The results show that all ceramics exhibit a single perovskite structure.An appropriate amount of Pr3+ ions enter the A-site of the crystal and form defect dipoles with oxygen vacancies,which significantly reduces the concentration of oxygen vacancies in the ceramic and enhances activation energy of conductivity from 0.38 eV to 1.57 eV,thus obtaining good energy storage density and efficiency.In addition,ceramics exhibit obvious upconversion luminescence properties.At an excitation wavelength of 980 nm,ceramics exhibit a significant green light emission peak with a center at 537 nm,corresponding to the energy level transition of Pr3+:3P0→3H6.0.97(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-0.03SrNb2O6-xwt%MgO(97BNBT-3SNO-xMgO)ceramics were successfully prepared by traditional solid-state reaction method.The phase structure,dielectric properties,electrical conductivity and energy storage properties of the ceramics were studied.The results indicate that all samples show a perovskite structure,exhibiting a dense and uniform microstructure and fine grain size.Among them,the sample with doping amount of x=0.3 exhibits the best dielectric temperature stability(△ε’/ε’200℃±15%)over a wide temperature range from 45℃ to 418℃,and has a relatively high dielectric constant in the 200℃(2299).Under the electric field intensity of 130 kV/cm,a high energy storage density of Wrec=1.84 J/cm3 and a high energy storage efficiency of 62.6%can be obtained.This work shows that adding oxides with high breakdown field strength are effective ways to prepare BNT-BT-based lead-free ceramic materials with high energy storage characteristics. |
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