Enhancement of microwave dielectric behavior by substitution of W⁶⁺ for Mo⁶⁺ in Li₂Mg_1.91Na_0.18M_o3O₁₂ ceramics

Abstract

Microwave dielectric ceramics with low dielectric constants are widely used in the design and fabrication of microwave devices. Here, low-temperature sintered Li2Mg1.91Na0.18Mo3-x W x O12 (LMNMWO) (x takes values from 0 to 0.15) ceramics are prepared by the solid-phase reaction technology. XRD and BSE patterns indicated that W6+ is solidly dissolved into the lattice and exhibits an overall single phase. The dielectric properties of the ceramics are effectively enhanced by the substitution of Mo6+ for W6+. The trends of density and SEM microscopic morphology show that the trace W6+ substitution can effectively promote grain growth and enhance grain homogeneity. The results indicate that the Q×f values are related to the relative density and grain homogeneity. The EDS spectrum demonstrates that the ratio of elements is close to the chemical formula of Li2Mg1.91Na0.18Mo2.95W0.05O12. The trend of τf values is related to the lattice distortion generated when W6+ is irregularly solidified into the lattice. Specifically, dielectric properties of the substituted LMNMWO (x = 0.05) ceramics are determined as follows: εr = 8.3, Q×f = 48357 GHz, and τf = -59 ppm/°C.