Crystal structures, dielectric properties, and lattice vibrational characteristics of Zn1-xCaxWO4 (x=0-0.25) composite ceramics

In this work, Zn1-xCaxWO4 (x=0-0.25, ZCWO) composite ceramics were prepared by using the conventional solid-state sintering method at 1070 degree celsius. The impact of Ca2+ substitution on the lattice vibrational characteristics and dielectric responses of the ZCWO composite ceramics was investigated in detail. The formation of composite ceramics was verified by the Rietveld refined X-ray diffraction data of the ZCWO samples. The lattice vibrational characteristics were also identified and analyzed by the Raman and infrared reflection spectra combined with the theoretical simulations. The vibrational modes analysis of the Raman spectra showed that the internal modes of the ZCWO ceramics correspond to the vibrations of the W-O octahedrons. From the Fourier transform infrared reflectance spectra, the existence of three new vibrational modes of Au (315 cm(-1)), Au (834 cm(-1)), and Eu (885 cm(-1)) at x = 0.15-0.25 was observed, which belong to the modes of the CaWO4 ceramic. In addition, the intrinsic dielectric properties fitted by the four-parameter semiquantum model were in direct agreement with the theoretical values obtained from the Clausius-Mossotti & damping equations and the measured values. Besides, the contribution of each lattice vibrational mode to the intrinsic properties of the ZCWO ceramics was thoroughly studied, which shows that external mode 1 contributes the most to the intrinsic properties. The structureproperty relationships of the ZCWO ceramics were established using the Raman modes as a media. The optimum dielectric properties of the ZCWO ceramics were obtained when x = 0.25: epsilon(r) =13.98 (10.48 GHz), Q x f = 32,188 GHz.