Preparation And Microwave Dielectric Properties Of BaTi₅O₁₁ Ceramics

In recent years,information and communication technology has made unprecedented development.Ba O-Ti O₂ microwave dielectric ceramics have been widely used in the fields of dielectric resonators,dielectric filters,dielectric substrates,antennas and satellites because of their excellent microwave dielectric properties and low cost.Ba Ti₅O₁₁ ceramics have excellent dielectric properties.So far,Ba Ti₅O₁₁ has not been fully developed,because it is difficult to prepare pure single-phase Ba Ti₅O₁₁powder through solid-state reaction.In addition,the densification temperature of Ba Ti₅O₁₁ ceramics is close to the decomposition temperature of Ba Ti₅O₁₁ phase,which makes it difficult to sinter and compact.Moreover,Ba Ti₅O₁₁ ceramics have large resonance frequency and temperature coefficient,which is difficult to meet the needs of practical application.In this paper,Ba Ti₅O₁₁ powders and ceramics were prepared by solid-state reaction method and sol-gel method,respectively.The microstructures and microwave dielectric properties of Ba Ti₅O₁₁ ceramics were studied by adjusting process parameters,raw material ratio and adding additives,in order to obtain Ba Ti₅O₁₁ceramics with excellent microwave dielectric properties.The main research contents and results are as follows:1.BaTi₅O₁₁ powders were prepared by solid-state reaction with Ba CO₃ and Ti O₂as raw materials.It was found that single-phase Ba Ti₅O₁₁ powders could not be obtained at 800-1150℃.Cu O was introduced as an additive and single-phase Ba Ti₅O₁₁powders were successfully synthesized at 1050-1150℃.The role of Cu O was discussed by XRD and DSC:the introduction of Cu O promote the formation of mesophase Ba Ti₄O₉,accelerate the transformation from Ba Ti₄O₉ to Ba Ti₅O₁₁ phase,and stabilize Ba Ti₅O₁₁ phase without decomposition at 1150℃.2.The effects of CuO content on the sintering and microwave dielectric properties of Ba Ti₅O₁₁ ceramics were studied.It was found that the appropriate Cu O content promote the densification of ceramics and improve the dielectric properties of Ba Ti₅O₁₁ceramics.Cu²⁺replaces Ba²⁺into the lattice to form a solid solution,which causes lattice distortion and makes it in a state of high-energy activation,increases the migration rate of grain boundary,promotes the densification of ceramics,and changes the distortion of titanium oxide octahedron in Ba Ti₅O₁₁ structureτ_fadjust to 0.When adding 1 mol%Cu O,the microwave dielectric properties of Ba Ti₅O₁₁ ceramics sintered at 1060℃for 4 hours are as follows:ε_r=43.6,Q×f=35500 GHz,τ_f=0.90 ppm/℃.3.Single-phase BaTi₅O₁₁ powders were prepared by sol-gel method after heat treatment at 800℃for 4 hours.However,the densification temperature of sintered ceramics was close to the phase decomposition temperature,so it was difficult to obtain dense single phase Ba Ti₅O₁₁ ceramics.According to the above solid-state reaction method,Cu O can enter the lattice to form solid solution,promote sintering and makeτ_f was adjusted to near zero,so Cu O additive was introduced into Ba Ti₅O₁₁ powder to prepare ceramics.It was found that the introduction of Cu O significantly reduce the sintering temperature,and the dense microstructure was observed after sintering at1000℃for 4 hours.When 1 mol%Cu O is added,the dielectric properties of the ceramics are the bestε_r=45.8,Q×f=35700 GHz,τ_f=1.91 ppm/℃.