SiO2/Al2O3 ratio dependence of microstructures and dielectric properties in barium strontium titanate glass ceramics

(Ba, Sr)TiO3-Al2O3-SiO2 glass ceramic system with various SiO2/Al2O3 ratios was investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), dielectric spectroscopy and impedance spectroscopy. The XRD results demonstrated that the proper SiO2/Al2O3 ratio could promote the crystallization of the major crystalline phase from the glass matrix. The dielectric property investigations showed that the dielectric constant passes through a maximum value while the dielectric breakdown strength has a minimum value with increasing SiO2/Al2O3 ratio. Meanwhile, the complex impedance analyses suggest the resistance of the glass-crystal interface rapidly decreases and the capacitance of the crystal slightly decreases with the increase of SiO2/Al2O3 ratio. The relaxation mechanisms of the (Ba, Sr)TiO3 glass ceramics changed from localized relaxation to long range conductivity as the SiO2/Al2O3 ratio was increased from 1.43 to 1.83. The variations in the dielectric response and the activation energy of the glass-crystal interface in the (Ba, Sr)TiO3 glass ceramics with the ratio of 2.40 could be attributed to the crystallization of fresnoite phase.