Development of CaMgSi2O6 diopside glass ceramic as microwave dielectric material

Development of a CaMgSi₂O₆ diopside phase as a microwave dielectric material was attempted in the present work. A glass frit was made by mixing oxides of the MgO-CaO-2SiO₂-ZrO₂ system, melted at 1500°C and then quenched. The glass frit was pulverized and pressed to discs. Controlled annealing at various temperatures was carried out to produce CaMgSi₂O₆ diopside phase in the discs. The microstructural features, microwave dielectric properties and nucleating/growth mechanism of ZrO₂ added CaMgSi₂O₆ are analyzed using scanning electron microscope (SEM), transmission electron microscopy (TEM) and impedance spectroscopy. Experimental results demonstrated that an amorphous phase MgO-CaO-2SiO₂ and m-ZrO₂ were forms after melted at 1500°C, and a glass-ceramic structure of CaMgSi₂O₆ as well as a tetragonal zirconia (t-ZrO₂) was precipitated from amorphous matrix after thermal treatment at 950°C. The diopside phase without addition m-ZrO₂ reveals only weak crystallization. It is found the crystallization enhancement of CaMgSi₂O₆ specimen is significant due to heterogeneous nucleation. Quality factor of CaMgSi₂O₆ was remakedly enhanced by adding ZrO₂ nucleating agent, indicating nucleation and growth control of the diopside phase plays a primary role in the CaMgSi₂O₆ glass-ceramic system.