Chemical bond characteristics and infrared reflectivity spectrum of a novel microwave dielectric ceramic CaIn2O4 with near-zero τf

Abstract

Orthorhombic-structured CaIn2O4 ceramics with a space group Pca21 were synthesized via a solid-state reaction method. A high relative density (95.6 %) and excellent microwave dielectric properties (εr ∼11.28, Qf = 74,200 GHz, τf ∼ −4.6 ppm/°C) were obtained when the ceramics were sintered at 1375 °C for 6 h. The dielectric properties were investigated on the basis of the Phillips–Van Vechten–Levine chemical bond theory. Results indicated that the dielectric properties were mainly determined by the InO bonds in the CaIn2O4 ceramics. These bonds contributed more (74.65 %) to the dielectric constant than the CaO bonds (25.35 %). Furthermore, the intrinsic dielectric properties of the CaIn2O4 ceramics were investigated via infrared reflectivity spectroscopy. The extrapolated microwave dielectric properties were εr ∼10.12 and Qf = 112,200 GHz. Results indicated that ion polarization is the main contributor to the dielectric constant in microwave frequency ranges.