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

In this work, two novel CaASbWO 8 (A = Gd, La; named CGSWO and CLSWO) microwave dielectric ceramics were synthesized by a classical solid-state method. Remarkably, the outstanding microwave dielectric properties ( ε r  = 12.97, Q×f  = 45,034 GHz, and τ f  = −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 ε r  = 9.89, Q×f  = 61,326 GHz, and τ f  = 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 ε r , the ε theo 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 τ f values of CGSWO and CLSWO ceramics were opposite, which provided an opportunity to manufacture microwave ceramic devices with good temperature stability.