Microstructural evolution and microwave dielectric properties of MgO-CaO-2SiO<inf>2</inf> material system

Microstructural characteristics and microwave dielectric properties of MgO-CaO-2SiO ₂ glass-ceramic system for microwave components were investigated using Rietveld refinement method, transmission electron microscopy and microwave dielectric measurements. Different amount of monoclinic zirconia (m-ZrO ₂ ) nucleating agent was added into MgO-CaO-2SiO ₂ glass system to synthesize and enhance the quality factor (Q×f) of CaMgSi ₂ O ₆ diopside glass-ceramic for low sintering temperature process (from 850°C to 950°C). Experimental results reveal that the tetragonal (t)-ZrO ₂ forms in the amorphous MgO-CaO-2SiO ₂ matrix first, and then crystalline CaMgSi ₂ O ₆ phase is nucleated and grown around the t-ZrO ₂ after sintering due to heterogeneous nucleating from 850 °C. Formation of t-ZrO ₂ can be attributed to the diffusion of Ca ²⁺ and Mg ²⁺ into the m-ZrO ₂ and led to transformation to a t-ZrO ₂ . Rietveld refinement results show that the lowest amorphous content and the highest quality factors due to the CaMgSi ₂ O ₆ diopside phase formation and crystal growth when the specimens were sintered at 950°C for 2 hrs. Transmission electron microscopic investigations imply that structural and microstructural arrangements influence the microwave dielectric properties remarkably.