Phase Separation, Crystallization, and Microwave Dielectric Properties of MgO-Al2O3-SiO2-TiO2-La2O3 Glass-Ceramic.

The effects of heat treatment on phase separation, crystallization, and microwave dielectric properties of the 1MgO·1.2Al2O3·2.8SiO2·1.4TiO2·0.4La2O3 (in molar ratio) glass and glass-ceramic were investigated. The results show that the parent glass has a two-liquid phase separation structure, with a droplet phase rich in Al & Ti embedded in the matrix rich in Si. Heat treatment of the glass at 770°C leads to the enlargement of the liquid droplets and promotes the formation of crystals from the droplets. The initial crystalline phase perrierite appears after heat treatment of the parent glass at 850°C, and it is analyzed to precipitate from the Al&Ti-rich droplet phase. With increasing heat-treatment temperature from 850°C to 1250°C, the crystallization degree of the glass increases as the other main crystal phases rutile, cordierite and magnesium aluminotitanate precipitate successively from the material. As a summation of the phases present, the dielectric constant εr of the material after heat treatment at 950°C-1250°C fluctuates between 11.3 and 12.3, while the quality factor Q × f and the temperature coefficient τf go up firstly and then decrease with the peak at 1200°C, ranging from 8200 to 19,500 GHz and −57ppm/°C to 24 ppm/°C, respectively. [ABSTRACT FROM AUTHOR]