Crystal structures, Raman spectra, chemical bonds, and microwave dielectric properties of novel low-εr CaASbWO8 (A = Gd, La) ceramics with opposite temperature coefficients

Abstract

In this work, two novel CaASbWO8 (A = Gd, La; named CGSWO and CLSWO) microwave dielectric ceramics were synthesized by a classical solid-state method. Remarkably, the outstanding microwave dielectric properties (εr = 12.97, Q×f = 45,034 GHz, and τf = −16.29 ppm/°C) were achieved for CGSWO ceramics sintered at 1440 °C, and CLSWO ceramics sintered at 1300 °C possessed the excellent microwave dielectric properties of εr = 9.89, Q×f = 61,326 GHz, and τf = 0.55 ppm/°C. Bond valence, ionic polarizability, Raman spectroscopy and Phillips–Vechten–Levine (P-V-L) theory were used to study the internal lattice vibration and chemical bonds in detail, and the dielectric properties were explored from the internal factors. In comparison to the εr, the εtheo of CGSWO was found to be consistently underestimated, whereas CLSWO exhibited a contrasting pattern. This discrepancy was primarily attributed to the rattling and compressed effects of A-site cation. According to the analysis of P-V-L theory, W-O bond played an important role in regulating the Q×f value. Moreover, the τf values of CGSWO and CLSWO ceramics were opposite, which provided an opportunity to manufacture microwave ceramic devices with good temperature stability.