Preparation And Electrical Properties Of（SBT-BNT-Mn）@ZrO₂ Energy Storage Ceramics

Ceramic capacitors are widely used in various pulsed power devices because of their high power density,but their low energy storage density is the shortcoming of their application development.Although considerable energy storage density can be achieved by applying extremely high electric field to capacitors,the harsh application conditions make it more meaningful to develop ceramics that can achieve high energy storage density at low and medium electric field.Moreover,from the perspective of practical application,the good temperature stability of ceramics is the basis for its stable work.Sr_0.7Bi_0.2TiO₃（SBT）ceramics have high energy storage efficiency and breakdown strength,however,the low maximum polarization(P_max)limits its energy storage density.Additionally,and poor temperature stability of SBT ceramics cannot meet the requirements of changeable temperature applications.In this thesis,the energy storage density and the energy storage efficiency of SBT-based ceramics under medium or low electric field are improved by a solid solution technique,doping or coating processes,and its temperature stability and breakdown field strength are also improved.The specific research work is as follows:To increase the ceramic energy storage density and its temperature stability in a wide temperature range,it is increased the P_max of the SBT-based ceramics by adding the traditional ferroelectric Bi_0.5Na_0.5TiO₃（BNT）into the SBT lattice.The（1-x）Sr_0.7Bi_0.2TiO₃-x Bi_0.5Na_0.5TiO₃（denoted as（1-x）SBT-x BNT,x=0.00,0.15,0.30,0.45）ceramics were prepared by a solid-state reaction method.With the increase of BNT content,the P_max of the ceramics increases,leading to a gradual increase in the maximum dielectric constant（ε_m）as well as its corresponding temperature（T_m）also increases.Under the applied electric field of130 k V/cm,the P_max of 0.55SBT-0.45BNT ceramics increased to 33.90μC/cm² relative to pure SBT ceramics of 16.50μC/cm²,and the recoverable energy storage density(W_rec)is 1.49J/cm³ with the energy storage efficiency（η）of 70.9%.In the temperature range of 2.1℃～300.0℃,the capacitance temperature change rate（TCC）of the ceramics is within±15%.Using B-site acceptor Mn doping,the energy storage efficiency of 0.55SBT-0.45BNT ceramics is optimized since the ions disorder in lattice is enhanced and the defect dipoles are introduced.0.55SBT-0.45BNT-x%mol Mn（x=0.5,1.0,1.5,2.0,abbreviated as 0.55SBT-0.45BNT-x Mn）ceramics were prepared by the solid-state reaction method.Both the dielectric constant and the dielectric loss at room temperature show the same trend of decreasing first and then increasing.The ceramic dielectric loss is the smallest among all the samples when x=1.5.Under the applied electric field of 130 k V/cm,the energy storage efficiency of all the ceramics with x≤1.5 is greater than 85.0%.Under this condition,the W_rec of 0.55SBT-0.45BNT-1.5Mn ceramics is 1.23 J/cm³,andηis 85.4%.The breakdown field strength reaches 188 k V/cm,and the maximum W_rec of 0.55SBT-0.45BNT-1.5Mn ceramics reaches 2.08 J/cm³ withηof 83.5%.Finally,the breakdown strength and the maximum energy storage density of the ceramics are improved by coating ZrO₂with high resistance and wide band gap on the ceramic powders.The 0.55SBT-0.45BNT-1.5Mn ceramic powders were coated with ZrO₂ by a precipitation method,and the ceramics with n₁（0.55SBT-0.45BNT-1.5Mn）/n₂（ZrO₂）=6/1,12/1,18/1,24/1（denoted as 1/x Zr ceramic,x=6,12,18,24）were prepared respectively.The experimental results show that the ZrO₂ coating can reduce the grain size of ceramics（from 2.13μm to 1.75μm）,increase the breakdown field strength and the energy storage density of ceramics.All the prepared samples with ZrO₂ coatings meet the requirements of EIA X9T standard（in the temperature range of-55℃～200℃,-33%<TCC<22%）.Among them,the breakdown field strength of the 1/18 Zr ceramic sample reaches 249 k V/cm,and its W_rec is 2.70 J/cm³ with aηof 88.8%.Variable temperature P-E curve test at 205 k V/cm electric field shows that the energy storage density change rate of 1/18 Zr ceramics is within10%in the range of 20℃～140℃.