Sintering behavior and microwave dielectric properties of CaMgSi2O6 ceramics with Al2O3 addition

• Al2O3 addition in CaMgSi2O6 ceramics resulted in a new phase of Ca(Mg,Al)(Si,Al)2O6.
• The solubility limit of Al2O3 in Ca(Mg,Al)(Si,Al)2O6 ceramic was between 4 wt% and 8 wt%.
• Second phases of CaAl2Si2O8 and (Mg,Al)8(Si,Al)6O20 obtained as Al2O3 addition exceeded 8 wt%.
• The vacancies defects and liquid phase lowered the sintering temperature.

The effects of Al2O3 content on the densification, phase compositions, microstructure and microwave dielectric properties of CaMgSi2O6–Al2O3 ceramics were investigated. The Al2O3 addition in CaMgSi2O6 ceramics resulted in the presence of a new phase, e.g. Ca(Mg,Al)(Si,Al)2O6, and caused the emergence of Ca vacancies and O vacancies. The solubility limit of Al2O3 in Ca(Mg,Al)(Si,Al)2O6 was found to be 4–8 wt%, and second phases of CaAl2Si2O8 and (Mg,Al)8(Si,Al)6O20 were observed when the Al2O3 addition exceeded 8 wt%. Appropriate Al2O3 addition promoted the sintering process and lowered the densification temperature due to the vacancies defects caused by the Al3+ substitution for Mg2+ and Si4+ and the liquid phase originated from the second phases. Typically, good microwave dielectric properties of ϵr = 7.99, Q × f = 60,132 GHz and τf = −48.21 ppm/°C were obtained when the Al2O3 addition was 12 wt% and the as-prepared composite ceramic was sintered at 1250 °C.

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