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

• Orthorhombic-structured CaIn 2 O 4 ceramics with a space group Pca2 1 were synthesized via a solid-state reaction method. • Excellent microwave dielectric properties (ε r ∼ 11.28, Qf = 74,200 GHz, τ f ∼ −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 and infrared reflectivity spectroscopy. • The dielectric properties of CaIn 2 O 4 ceramics were mainly determined by the In–O bonds, and these bonds contributed more (74.65%) to the dielectric constant than the Ca–O bonds (25.35%). Orthorhombic-structured CaIn 2 O 4 ceramics with a space group Pca2 1 were synthesized via a solid-state reaction method. A high relative density (95.6 %) and excellent microwave dielectric properties (ε r ∼11.28, Qf = 74,200 GHz, τ f ∼ −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 CaIn 2 O 4 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 CaIn 2 O 4 ceramics were investigated via infrared reflectivity spectroscopy. The extrapolated microwave dielectric properties were ε r ∼10.12 and Qf = 112,200 GHz. Results indicated that ion polarization is the main contributor to the dielectric constant in microwave frequency ranges. [ABSTRACT FROM AUTHOR]