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 (er ∼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 In O bonds in the CaIn2O4 ceramics. These bonds contributed more (74.65 %) to the dielectric constant than the Ca O bonds (25.35 %). Furthermore, the intrinsic dielectric properties of the CaIn2O4 ceramics were investigated via infrared reflectivity spectroscopy. The extrapolated microwave dielectric properties were er ∼10.12 and Qf = 112,200 GHz. Results indicated that ion polarization is the main contributor to the dielectric constant in microwave frequency ranges.