Preparation Of Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃-based Fine-grained Ceramics With Double-layer Core-shell Structure And Study On Dielectric And Energy Storage Properties

With the development of the electronics industry,multilayer ceramic capacitors?MLCCs?develop toward large capacity,miniaturization and high energy density,which require the dielectric materials not only with fine-grained structure,but also with high capacity and energy storage density.Therefore,to improve the breakdown strength and dielectric constant of the ceramics become the key factors.In this paper,BaTiO₃ and Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃?BSZT?micro-nano powders were synthesized by atmospheric pressure aqueous phase method.The La₂O₃,MgO or Al₂O₃ coated on the surface of the monodisperse BaTiO₃ or BSZT particles using precipitation method.And then SiO₂ or ZnO-B₂O₃-SiO₂?ZBSO?were coated by sol-precipitation method to obtain the fine-grained ceramics with high dielectric constant,high breakdown strength and good temperature stability to lay the theoretical basis for the energy storage applications of MLCCs.The main research contents are as follows:?1?We improved the dispersion and uniformity of the powders to obtain BSZT-based fine-grained ceramics.The monodisperse BSZT micro-nano powders were prepared by atmospheric pressure aqueous phase method.Then,the mesoporous SiO₂ and mesoporous ZBSO were coated on the surface of BSZT by precipitation and sol-precipitation method,respectively.The dispersion of the BSZT@mSiO₂ and BSZT@mZBSO powders is good,and the "shell" has a clear mesoporous structure.The maximum dielectric constant of BSZT@SiO₂ and BSZT@mSiO₂ ceramics are 441 and810 respectively,and the storage densities are 0.21 J/cm³ and 0.27 J/cm³,respectively.The maximum dielectric constant of BSZT@ZBSO and BSZT@mZBSO are 563 and716 respectively,and the energy storage densities were 0.34 J/cm³ and 0.36 J/cm³,respectively.The dielectric constant and the energy storage density of the ceramics prepared by the mesoporous coating are higher than those of the non-mesoporous materials,but still need to be further improved.?2?We first tested to get fine-grained ceramics with higher breakdown strength through the double layer "core-shell" structure to give new ideas developing energy storage ceramic materials of MLCCs.Monodispersed BaTiO₃ micro-nano powders were prepared by atmospheric pressure aqueous phase method.The rare earth oxide modifier La₂O₃ was coated on the surface of BaTiO₃ particles and SiO₂ was coated on the outermost layer to obtain spherical BaTiO₃@La₂O₃@SiO₂ micro-nano powders with double-layer "core-shell" structure.The powders have high dispersion and uniformity.The effects of the different content SiO₂ on morphology,phase composition of the powders and ceramics and dielectric properties and energy storage properties of the ceramics were studied.The average particle size of the powders is about 280 nm,the interlayer La₂O₃ is about 3 nm and the outermost SiO₂ is about 17 nm.It was found that the dielectric properties of the ceramics met the X8 R standard,and the dielectric constant and energy storage density of the ceramics increased first and then decreased with the increase of SiO₂ amount.When the content of SiO₂ is 9.0 wt%,the energy storage density of the ceramics reached the maximum value of 0.54 J/cm³,and the corresponding breakdown field is the highest?13.6 kV/mm?.The dielectric constant of ceramic is the highest at 6.0 wt%.The idea of the particles with double-layer "core-shell" structure were designed to obtain fine-grained ceramics with a high breakdown strength,which will lay the foundation for the study of MLCCs for energy storage.?3?In order to improve the breakdown strength of the material,fine-grained ceramics with high energy storage density were prepared,and the breakdown strength was improved by replacing the BaTiO₃ with the relaxed ferroelectric BSZT and the high breakdown strength MgO instead of La₂O₃ to further improve its energy storage density.The monodisperse BSZT micro-nano powders were prepared by atmospheric pressure aqueous phase.MgO was coated on the surface by precipitation method.The ZBSO composite sintering agent was further coated on the surface of BSZT@MgO particles by sol-precipitation method.The particle size of the powders is about 270 nm,and the thickness of the MgO and ZBSO shells are about 7 nm and 14 nm,respectively.The effects of different content ZBSO on the morphology,phase composition of powders and ceramics and dielectric and storage properties of ceramics were studied.It is found that the storage energy density and dielectric constant increase first and then decrease with the increase of ZBSO coating amount.When the ZBSO amount is 2.0 wt%,the dielectric constant reaches the maximum value of 6026.When the amount is 4.0 wt%,the ceramic has the largest energy storage density of about 0.71 J/cm³,and the breakdown strength of the ceramics increases from 17.4 to 24.1 kV/mm.It can be seen that the energy density and breakdown strength of the B SZT@MgO@ZB SO ceramics are significantly improved compared to BaTiO₃@La₂O₃@SiO₂.?4?In order to further improve the breakdown strength of the ceramics,adding Al₂O₃ in the middle layer to form MgO-Al₂O₃ composite,and MgAl₂O4 spinel phase with high breakdown strength will form.The BSZT@MgO-Al₂O₃@ZBSO micro-nano powders with double-layer "core-shell" structure were prepared by precipitation method,and the thickness of MgO-Al₂O₃ composite layer and ZBSO were about 8 nm and 13 nm,respectively.The effects of different Mg/Al ratios on the phase composition,microstructure and dielectric properties of the ceramics were investigated.The results show that with the decrease of Mg/Al ratio and the increase of Al₂O₃ amount,the dielectric strength and dielectric density of BSZT@MgO-Al₂O₃@ZBSO ceramics are increased and then decreased.When the Mg/Al ratio is 2:1,the ceramic has the maximum dielectric constant of 3143 and the maximum energy storage density of 0.91J/cm³.When the Mg/Al ratio is 1:1,the ceramic has the maximum compressive strength?29.40 kV/mm?.It can be seen that the breakdown strength of the BSZT@MgO-Al₂O₃@ZBSO ceramics are significantly improved,and the energy storage density is also significantly increased.?5?In order to further improve the dielectric constant of BSZT@MgO-Al₂O₃@ZBSO ceramics,we added La₂O₃ in the middle layer.The BSZT@MgO-Al₂O₃-La₂O₃@ZBSO micro-nano powders and ceramics with double-layer "core-shell" structure were prepared by precipitation method.The effects of different content La₂O₃ on the phase composition,microstructure and dielectric properties of ceramics were studied.The results show that the dielectric constant and polarization intensity of ceramics increase first and then decrease with the increase of La₂O₃ amount.When the amount of La₂O₃ is 0.8 mol%,the ceramic has the highest dielectric constant of 4988,and the maximum energy density is1.06 J/cm³.When the La₂O₃ amount is ? 0.8 mol%,the TCC conforms to the X8R standard.It can be seen that the energy storage density of the ceramics is obviously increased,and its dielectric properties meet the X8 R characteristics,which will provide a new idea for the development of energy storage medium materials of MLCCs.