Vibrational spectroscopy and microwave dielectric properties of two novel Ca3Ln2W2O12 (Ln = La, Sm) tungstate ceramics

Abstract Two novel tungstate ceramics with a nominal composition of Ca3Ln2W2O12 (Ln = La, Sm) were prepared via standard solid-state reaction methods. According to X-ray diffraction patterns, both ceramics crystallized in hexagonal crystal systems with a space group of R 3 ¯ m (No. 166). The vibrational modes of the Raman spectra were identified, and the evolutions of the wavenumber and the full width at half maximum (FWHM) were analyzed. The optimum microwave dielectric properties with er = 18.7, Qf = 50,500 GHz, and τf =–90 ppm/oC were realized in Ca3La2W2O12 ceramics, while moderate Qf values were obtained in the Sm composition (er = 19.5, Qf = 15,700 GHz, and τf =–95 ppm/oC). The discrepancy in the Qf values was associated with the broader FWHM of Raman spectra and smaller grain sizes. Infrared reflectivity (IR) spectra were also used to determine the intrinsic dielectric loss, where more damped phonon parameters were also identified in Ca3Sm2W2O12 ceramics.