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 high quality factor was successfully prepared at temperatures below 950 °C. The linear shrinkage for 50 vol% ZBS glass–ZnAl2O4 composite showed a steep increase up to 650 °C and a plateau between 700 °C and 950 °C, implying that one-stage densification process occurred. The crystallization of ZnAl2O4 was observed above 700 °C and an insufficient densification occurred due to the consumption of the glass. As the sintering temperature increased, the quality factor (Q × f0) 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 Q × f0; a high value of 17,757 GHz (1415 at 12.6 GHz) was obtained for the specimen sintered at 900 °C.