Microstructural evolution and microwave dielectric properties of MgO-CaO-2SiO2 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.