Study On Low Temperature Sintering And Ions Substitution Of Li₂ZnTi₃O₈Microwave Dielectric Ceramics

The Li₂ZnTi₃O₈ceramics exhibited excellent microwave dielectric properties,and was well sintered at1075°C. Although, it could densify Li₂ZnTi₃O₈ceramicefficiently sintered at1075°C without sintering aids, further researches are stillrequired for lowering the sintering temperature to about900°C so that it could beco-fired with silver electrode.Firstly, the paper systematically studied the sintering temperature,microstructures and the relationship between structures and microwave dielectricproperties of a series of foundation and technical problems of Li₂ZnTi₃O₈ceramics.The optimal technological parameters of Li₂ZnTi₃O₈ceramics preparation weregained. When the Li₂ZnTi₃O₈ceramics calcined at900°C, secondary ball milled for4h and sintered at1080°C, the best microwave dielectric properties of εr=25.4, Qf=76,600GHz, τf=-11.6ppm/°C were obtained.In order to achieve the low temperature sintering of Li₂ZnTi₃O₈ceramics, threekinds of sintering additives of H₃BO₃、MgO-B2O3-SiO2（MBS）、ZnO-B2O3-SiO2（ZBS）were doped, respectively. The sintering temperature could be decreased to880°Cwith1.0wt%H₃BO₃addition. The sintering temperature of Li₂ZnTi₃O₈ceramicscould be decreased to900°C with2.0wt%MBS or ZBS glasses. Addition ofLi₂ZnTi₃O₈ceramics with1.0wt%H₃BO₃sintered at880°C/4h has εr=25.9, Q×f=50,200GHz, and τf=-6.8ppm/°C. Addition of Li₂ZnTi₃O₈ceramics with2.0wt%MBS sintered at900°C/4h has εr=25.4, Q×f=56,200GHz, τf=-9.9ppm/°C, andaddition of Li₂ZnTi₃O₈ceramics with2.0wt%ZBS sintered at900°C/4h has εr=24.4, Q×f=52,400GHz, τf=-14.4ppm/°C.In order to improve the microwave dielectric properties of Li₂ZnTi₃O₈ceramics,the effects of A and B site ions substitutions on the microwave dielectric properties ofLi₂ZnTi₃O₈ceramics due to changes in chemical composition, density andmicrostructure were investigated. In the Li2Zn（Ti1-xSnx）3O8system, Sn⁴⁺substitutionincreased the Q×f values while decreased the εrvalues and τfvalues. The microwave dielectric properties of εr=22.1, Q×f=79,500GHz, τf=-24ppm/°C were obtainedwhen Li2Zn（Ti0.8Sn0.2）3O8ceramics sintered at1080°C for4h. In theLi₂Zn（Ti1-xZrx）3O8system, the τfvalues were improved while the Q×f and εrvalueswere decreased when Ti⁴⁺substituted by Zr⁴⁺. Li2Zn（Ti0.8Zr0.2）3O8ceramics showedan excellent combination of microwave dielectric properties with εr=22.6, Q×f=66,500GHz, τf=-8.7ppm/°C when sintered at1120°C for4h. In theLi2（Zn1-xMgx）Ti3O8system, the Q×f values were decreased while the εrvalues wereincreased and the τfvalues were improved greatly when Zn2+substituted by Mg2+. TheLi2（Zn0.2Mg0.8）Ti3O8dielectric ceramics composition showed the best dielectricproperties with εr=26.8, Q×f=42,400GHz, τf=-1.8ppm/°C.