The dielectric properties of certain ZnO-Al₂O₃-SiO₂ glass-ceramics

Abstract

An original study has been made of the influence of additions of alkaline-earth metal oxides (CaO, SrO, BaO) at the expense of ZnO on the dielectric properties of certain ZnO-Al₂O₃-SiO₂ glass-ceramics. Tests were carried out at 20° C at frequencies of 10⁵ to 10¹⁰ Hz and at temperatures up to 400° C at a frequency of 9.37 × 10⁹ Hz. X-ray diffraction analysis showed that the major crystalline phase in all cases was Zn₂SiO₄ and this was little changed in proportions or lattice parameters by the additions. Some changes in secondary crystal phases were noted but no positive identification of crystals containing Ca²⁺, Sr²⁺ or Ba²⁺ was made. It is concluded that the alkaline-earth metal ions are essentially contained in the residual glassy phase and that the major contribution to the dielectric losses is by the residual glassy phase. Increase in the BaO content causes a loss peak to move to lower frequencies (in the range > 10¹⁰ to 10⁸ Hz) and this is believed to be partly due to the BaO additions rendering the network of the residual glassy phase more open, and partly due to the heavy mass of the Ba²⁺ ions. A similar effect was not observed for additions of CaO and SrO. Furthermore, it appears that the alkaline-earth metal oxide additions are restricting deformation of the network of the residual glassy phase.