Microwave Dielectric Composite Consisted By BMT Coated With ZrO₂ And LMASZ Glass-ceramic

The composites of glass-ceramic and BMT(Ba(Mg_1/3Ta_2/3)O₃) coated with ZrO₂ through the method of sol-precipitation were prepared.The microwave dielectric properties were measured for samples with different volumes content of BMT and heating treatment scheme.The phase composition was characterized by XRD and SEM, the relationship of which and the dielectric properties was discussed.It was showed that the reaction between BMT and glass-ceramic was restrained due to the BMT coated with ZrO₂.The composites came into being on the condition that the BMT was coated well with ZrO₂;otherwise,the BMT would react with glass-ceramic and disappeared.The extent of the reaction between BMT and glass-ceramic was sensitive to the thickness of the ZrO₂ layer,the thicker the coating,the better the restraining,however,the ZrO₂ would flake off from the BMT if the coating was too thick.It was found that the densification of the composition would be inhibited by the BMT;the density of the composition would decrease with the increase of the BMT content.The expected increase of dielectric constant was counteracted by the porosity.The ZrO₂ coating did favor to holding BMT,while,the Q value would decreased because of the thicker coating.TheÏ„_εof the samples were determined by the phase composition and their content。The heating procession for the specimen at 600℃did favor to the crystallization of ZnAl₂O₄,with the holding time prolonging,the content of ZnAl₂O₄ increased,the grain coarsed,the ordering degree elevated,the glass phase decreased,the Q value enhanced and theÏ„_εmoved to the negative direction.In the experiment,two samples presented excellent dielectric properties: one withε_r=9.51,Q=1116.1,Ï„_ε=-5.4 ppm/℃(B30 sintered at 1020℃,then heating at 600℃for 12h),the other withε_r=9.70,Q=1159.3,Ï„_ε=4.5 ppm/℃(B30 sintered at 1050℃,then heating at 600℃for 12h).