Temperature-dependent dielectric and Raman spectra and microwave dielectric properties of gehlenite-type Ca₂Al₂SiO₇ ceramics

Gehlenite-type Ca₂Al₂SiO₇ ceramics were prepared by the conventional solid-state reaction. Two anomalies were found in the plot of dielectric constant vs temperature, which were associated with space charge polarization. Pure phase crystal structure and no phase transition were observed in the temperature-dependent X-ray diffraction (XRD) patterns and Raman spectra from room temperature (RT) to 900°C. There was relevant relation between Q × f and τ_ƒ with the stretching vibrations of Ca-O bond and O-Ca-O bending in CaO₈ polyhedron. Excellent microwave dielectric properties (ε_r = 8.86, Q × f = 22 457 GHz, and τ_f = −51.06 ppm/°C) were obtained for Ca₂Al₂SiO₇ sintered at 1440°C in air, which had the potential application to use in microwave and millimeter-wave devices such as capacitors and substrates.