Crystal structure, Raman spectra, and microwave dielectric properties of high-Q Li2ZnTi3O8 systems with Nb2O5 addition

Li2ZnTi3O8(LZT)-xwt.%Nb2O5 (x = 0, 1, 2, 3, 4) microwave dielectric ceramics were synthesized by the conventional solid-phase sintering method. The effect of Nb2O5 addition on crystal structure, Raman spectra, and dielectric properties were studied. X-ray diffraction results indicated that the maximum crystallinity of LZT ceramics were obtained at 1075 degrees C, and that Nb5+ diffused into the LZT matrix completely to form a stable solid solution. XRD refinement results demonstrated that the substitution of Nb5+ for Ti4+ caused the cell volume to increase. The microscopic morphology of LZT-xwt.%Nb2O5 (x = 0, 1, 2, 3, 4) ceramics were further investigated by scanning electron microscopy, and results indicated that Nb2O5 could promote the grain growth and sintering of LZT ceramics. Extrinsic and intrinsic dielectric losses were studied through Raman and impedance spectroscopy. The highest value of quality factor x resonant frequency (Q x f) was attributed to the increase in relative density and reduced number of oxygen vacancies (V-O(center dot center dot)), as well as the decrease in damping behavior. Moreover, the dielectric constant (epsilon(r)) showed the same trend as cell polarization and the temperature coefficient of resonant frequency (tau(f)) was inversely proportional to cell volume. The LZT ceramics with 3 wt% Nb2O5 addition sintered at 1075 degrees C for 4 h exhibited the optimal microwave properties, i.e., epsilon(r) = 26.52, Q x f = 66 304 GHz, and tau(f) = 14.2 ppm/degrees C.