Preparation And Dielectric Properties Of Oxide-coated Barium Strontium Titanate Ceramics

Barium strontium titanate(Ba_1-xSr_xTiO₃,BST),as an environmental-friendly ferroelectric material,is widely used in multilayer capacitors,filters,Varactors,DRAM,infrared detectors and other electronic components due to its simply and easily adjustable curie temperature and electrical properties.Its performance can be controlled through ion doping modification,multi-phase composite modification and surface coating modification in order to make BST better meet the performance requirements of various devices.A systematic study on oxide composite barium strontium titanate ceramics was carried out in this dissertation.In this dissertation,Ba_0.6Sr_0.4TiO₃ was selected as the research object.The effects of sol-gel method and co-precipitation method on the preparation of Ba_0.6Sr_0.4TiO₃ powders and the influence of reaction conditions on the powder morphology were systematically investigated.Afterwards,the BST powder with homogeneous morphology was selected as the substrate for the coating reaction,the core-shell structure Ba_0.6Sr_0.4TiO₃@Fe₂O₃ and Ba_0.6Sr_0.4TiO₃@Al₂O₃ were fabricated by chemical precipitation.The process and the formation mechanism of the core-shell microstructure were studied.Based on this,Ba_0.6Sr_0.4TiO₃@Fe₂O₃ and Ba_0.6Sr_0.4TiO₃@Al₂O₃ composite ceramics were prepared,the sintering mechanism and the influence of ceramic microstructure on the dielectric properties was studied.The research shows that:controlling the reaction temperature of tetrabutyl titanate and oxalic acid solution at 80°C in the co-precipitation method can obtain rhombohedral particles with uniform morphology;The composite powder of Ba_0.6Sr_0.4TiO₃@Fe₂O₃ core-shell structure was obtained 600°C by chemical precipitation using nitrate;BST-based ceramics were sintered at 1200°C for 2 hours with Ba_0.6Sr_0.4TiO₃@Fe₂O₃ powder as raw material.It was considered that Fe₂O₃ enters Ba_0.6Sr_0.4TiO₃ lattice at high temperature,resulting in the generation of second phase,which had a significant effect on the density and dielectric properties of the material:It had obvious grain refinement effect,the curie peak obviously decreased and broadened,and the dielectric temperature stability at low temperature?-150²5°C?increased when the content of Fe₂O₃ is less than 5wt%;the density and dielectric properties of ceramics decreased when Fe₂O₃ content is too high?>5wt%?;Al₂O₃ coating modification appeared to be notably different from Fe₂O₃ coating modification,The dielectric properties decrease with the increase of coating amount when the content of Al₂O₃ is less than5wt%.