Raman spectra, infrared spectra, and microwave dielectric properties of low-temperature firing [(Li_0.5Ln_0.5)_1-xCa_x]MoO₄ (Ln = Sm and Nd) solid solution ceramics with scheelite structure

In this work, a series of scheelite solid solution [(Li_0.5Ln_0.5)_1-xCa_x]MoO₄ (Ln = Sm and Nd; x = 0.20, 0.40, 0.60, 0.70, 0.80, 0.85, 0.90) ceramics were prepared by conventional solid-state reaction method. The sintering temperature was lowered to 925C by (Li_0.5Ln_0.5)²⁺ substituting for Ca²⁺ in the solid solution without any secondary phase. Compared with that of scheelite CaMoO₄ (-57 ppm/C), the temperature coefficient of resonant frequency (TCF or τ_f) of the scheelite solid solution was modified to near zero (about +4.3 ppm/C) at x = 0.8 with a dielectric constant 11.0 and the quality factor (Q × f value) of 18 695 GHz. The Raman spectra, showed the degree of disordering increased with x value, which resulted in decrease in the permittivities and increase in the Q × f values. The infrared spectra were analyzed using the classical harmonic oscillator model and were extrapolated to the microwave range. The chemical compatibility with silver electrode indicated that the reported series of ceramics were good candidates for the low-temperature cofired ceramic applications.