The Research On BaTiO₃-BiMeO₃ Based Dielectric Ceramics Fabrication And Property

In recent years,pulsed capacitors as the core energy storage element in pulse power technology with higher energy storage density and power density are urgently needed to meet the growing demand in pulsed power technology toward high repetition frequency pulsed power,miniaturization and high reliability.As the core component of the pulsed capacitor,the dielectric material directly determines the performance of the pulsed capacitor.Ceramic dielectric materials are considered to be the promising energy storage dielectric materials due to their ultra-high power density,rapid charge and discharge capability,wide temperature and frequency range,and high cycle life.However,the relatively low recoverable energy density and efficiency of dielectric ceramics failure to help the development of energy storage device miniaturization and integration.BaTiO3-based ceramics are attractive lead-free ferroeelctric ceramics due to their high dielectric constant and polorization as one of lead-free energy storage materials alternatives.In this thesis,we focused on BT-based relaxor ferroelectric ceramics,trying to develop a new kind of high energy storage and high energy effiency dielectric materials.The specific research contents are as follows:1.The X-ray diffraction results showed that(1-x)BaTiO3-xBi(Zn1/2Zr1/2)O3(x=0.04-0.20)ceramics were crystalized as the perovskite structure,and there was no secondary phase in whole compositional range.For x=0.04,the ceramics were in tetragonal phase,and transformed to a pesudocubic phase for x=0.08 at ambient temperature.Temperature-dependent dielectric measurements indicated a crossover from ferroelectric behavior to relaxor-like characteristics.As the xBi(Zn1/2Zr1/2)O3 content increased,the polarization-electric field hysteresis loops became slimmer,and the discharge energy density increased firstly,but dropped.For x=0.12,the maximum discharge energy density was 0.76 J/cm3 at 100 kV/cm,and the corresponding energy eff-iciency was 98.0%,indicating that(1-x)BaTiO3-xBi(Zn1/2Zr1/2)O3 ceramics were promising candidates for energy storage applications.2.XRD and TEM analysis indicted that the(1-x)BaTiO3-xBi(Ni1/2Zr1/2)O3 ceramics exhibited perovskite structure(pesudocubic phase).The 0.86 BaTiO3-0.14Bi(Ni1/2Zr1/2)O3 ceramics with high breakdown strength(230 kV/cm),hihg recoverable energy density(1.70 J/cm3),and high energy efficiency(94%)were prepared.3.With an increasing concentration of Bi(Ni1/2Sn1/2)O3,(1-x)BaTiO3-xBi(Ni1/2Sn1/2)O3 solid solutions displayed a phase transition from tetragonal symmetry to pseudocubic symmetry with highly diffusive and frequency-dependent relaxor ferroelectric behavior.Modified by Bi(Ni1/2Sn1/2)O3,(1-x)BaTiO3-xBi(Ni1/2Sn1/2)O3 ceramics yielded slim polarization-electric field loops and improved energy-storage performances.The optimal energy storage properties can be achieved at x=0.10,and samples showed a high recoverable energy density of 2.52 J/cm3 and a remarkably high energy efficiency of 93.8%under 240 kV/cm simultaneously at ambient temperature,which represent enhancements by 925%and 286%,respectively,over pure BaTiO3.The energy storage characteristics of the 0.9BaTiO3-0.1Bi(Ni1/2Sn1/2)O3 ceramic manifested good thermal stability(-55?150 0C)and frequency stability(10 Hz-1 kHz),with a variation in recoverable energy density of less than 10%.Meanwhile,the pulsed charging-discharging measurement showed that the 0.90BaTiO3-0.10Bi(Ni1/2Sn1/2)O3 ceramic had a large power density of 19 MW/cm3.4.Introducing Bi(Mg1/2Sn1/2)O3 into the BaTiO3 host triggered a ferroelectric-to-relaxor phase transition,which yielded slim polarization-electric field loops and enhanced energy-storage performances.It was found that large recoverable energy density with 2.25 J/cm3 and high energy efficiency of 94.0%were obtained simultaneously under 240 kV/cm with x=0.12.Furthermore,the energy storage characteristics of the 0.88BaTiO3-0.12Bi(Mg1/2Sn1/2)O3 ceramic exhibited good temperature stability in the range of-55?150?,and great frequency stability in the range of 10-1000 Hz.Meanwhile,by means of pulsed charging-discharging evaluation,the 0.88BaTiO3-0.12Bi(Mg1/2Sn1/2)O3 ceramic displayed a large power density of 27.7 MW/cm3.5.Bi(Mg2/3Ta1/3)O3 modified BaTiO3 are demonstrated to be viable cadi dates for energy storage.The grain grow can be effectively inhibited by Bi(Mg2/3Ta1/3)O3 doped into BaTiO3.When x?0.03,the average grain size is less than 1 ?m,which is benifitie for enhancing breakdown strenght and the hihgest breakdown strength can be obtained at x=0.20.Herein,0.87BaTiO3-0.13Bi(Mg2/3Ta1/3)O3 ceramics were developed with excellent dielectric temprature stability and energy storage properties:a capacitance variation satisfying the X7R specification;a high recoverable energy density(3.04 J/cm3)and an energy efficiency(95.6%),while keeping insensitive to thermal stimulus over-55?150? and frequency stimulus over 10?100 Hz.Futhermore,the pulsed discharge capability of 0.87BaTiO3-0.13Bi(Mg2/3Ta1/3)O3 ceramics were muasured under different electric fieds,showing a high power density of 39.3 MW/cm3.