Low-temperature preparation and microwave dielectric properties of ZBS glass–Al2O3 composites

The preparation and microwave dielectric properties of ZnAl2O4-based glass-ceramic composites were investigated. Using zinc borosilicate (ZBS) glass and Al2O3, glass-ZnAl2O4 composites with a high quality factor were prepared at temperatures below 950 C. The linear shrinkage of 50 vol% ZBS glass-ZnAl2O4 composites showed a steep increase up to 650 C and a plateau between 700 and 950 C, implying that a one-stage densification process occurred. The crystallisation of ZnAl2O4 was observed above 700 C and insufficient densification occurred due to the consumption of the glass. As the sintering temperature increased, the quality factor (Qxf0) showed an increase with an S-type curve whereas the dielectric constant was almost constant. The formation of ZnAl2O4 might correspond to the increase of Qxf0; a high value of 17757 GHz (1415 at 12.6 GHz) was obtained for the specimen sintered at 900 C.