The Study Of Low-temperature Sintering And Dielectric Properties Of Li₂MgTi₃O₈Microwave Dielectric Ceramics

In recent years, with the rapid development of microwave communicationtechnology, the continuing development of microwave dielectric materials forapplications including substrates, resonators, filter, and antennas used in wirelesscommunication systems demands new low-cost dielectrics with high performance.The spinel structure microwave dielectric ceramics Li₂MgTi₃O₈were used as studiedobject, and the specimens were prepared by conventional solid state mixed method.The bulk density, microstructure effect on the microwave dielectric properties ofLi₂MgTi₃O₈ceramics were studied by using X-ray powder diffraction, scanningelectron microscopy.First of all, preparation techniques of Li₂MgTi₃O₈ceramics were studied. Theeffect of calcining temperature, milling time, and sintering temperature on themicrostructure and dielectric properties has been investigated. The results showed that,good microwave dielectric properties of ε_r=27.3, Q×f=38867GHz could obtainedin Li₂MgTi₃O₈ceramics when calcined at900oC, milled12h, and sintered at1075oCfor4h. The bulk density was3.335g/cm³, which was equivalent to a relative densityof about95.25%of the theoretical density, ε_r=31.17, tanδ=9.87×10-4at1MHz.Secondly, BCB was added into Li₂MgTi₃O₈ceramics as the sintering aids inorder to lower the sintering temperature. The sintering behavior and microwaveproperties were investigated, and the results were shown as followed. The bestmicrowave properties of Li₂MgTi₃O₈ceramics were ε_r=26.1, Q×f=24827GHz,when1.0%BCB was added and sintered at950oC. The bulk density was3.160g/cm³,which was equivalent to a relative density of about91.3%of the theoretical density,and it belonged to liquid sintering mechanism.Finally, according to the ion radii size, Zn²⁺，Co²⁺，Mn²⁺were substituted Mg²⁺inLi₂MgTi₃O₈ceramics, and Li₂Mg_1-xM_xTi₃O₈（M=Zn, Co, Mn）, x=0.02⁰.08werefabricated. A single-phase Li₂MgTi₃O₈cubic structure was formed and no secondaryphase could be observed in the diffraction patterns. With addition of ZnO, grain sizesincreased, and good microwave dielectric properties of ε_r=26.58, Q×f=44800 GHz could be obtained in Li₂MgTi₃O₈ceramics doped with6wt%ZnO. The bulkdensity was3.360g/cm³, which was equivalent to a relative density of about95.8%ofthe theoretical density. The doping of Co₂O₃could improved the density of theceramic, and good microwave dielectric properties of ε_r=26.6, Q×f=42500GHzcould be obtained in Li₂MgTi₃O₈ceramics doped with6wt%Co₂O₃when sintered at1075oC. The doping of MnO₂reduced the grain sizes, and good microwave dielectricproperties of ε_r=25.8, Q×f=36800GHz could be obtained in Li₂MgTi₃O₈ceramics doped with6wt%MnO₂when sintered at1075C. The bulk density was3.351g/cm³, which was equivalent to a relative density of about95.1%of thetheoretical density.