Structure, bond characteristics, electrical and microwave dielectric properties of melilite Ca2Ga2SiO7 ceramic with unique near-zero τ f

In this work, Si-based melilite Ca2Ga2SiO7 ceramics with low epsilon r and unique near-zero tau f were prepared, which formed a pure tetragonal structure with P-421m space group throughout the sintering temperature range of 1300 degrees C- 1400 degrees C. Optimal microwave dielectric properties (low epsilon r = 10.5 f 0.1, Q x f = 40,500 f 300 GHz, and near-zero tau f=-2.7 f 1.0 ppm/degrees C) and ultrahigh insulation resistivity (2.82x1012 S2 center dot m) were obtained at 1350 degrees C. The large positive deviations of 66.2 % and 17.9 % in A epsilon r and A alpha [A epsilon r = ( epsilon r ( Corr )- epsilon r (C-M) )/ epsilon r (C-M) , A alpha = ( alpha Corr- alpha m )/ alpha m ], respectively, were caused by the rattling effect of Ca2+ and Si4+. The unique near-zero tau f was governed by the rattling effect, resulting in positive tau alpha m of 33.4 ppm/degrees C and negative tau epsilon of-21.0 f 0.1 ppm/degrees C. The inherent dielectric properties were extrapolated by the fitted infrared reflectance spectra.