Raman spectra and microwave dielectric properties of Na5Tm1-x(Y1/3Yb2/3)x(MoO4)4 ceramics with ultra-low sintering temperature

The Na5Tm1 - x(Y1/3Yb2/3)x(MoO4)4 ceramics (x=0-0.18) were successfully synthesized via the solid-state reaction method. XRD analysis revealed that they possessed a single-phase tetragonal scheelite structure belonging to the space group I4(1)/a(88). SEM analysis demonstrated that the samples sintered at 600 degrees C exhibited a dense microstructure, with a relative density as high as 94.9% and an average grain size ranging from 2.172 mu m to 2.424 mu m. The relative density serves as an external factor influencing epsilon r and Qxf, while tau f is related to bond valence. The ionicity of the Tm-O bond, and the lattice energy and bond energy of the Mo-O bond are the intrinsic factors determining epsilon r, Qxf, and tau f, respectively. Raman spectroscopy provided an intuitive characterization of the vibrational properties of the [MoO4]2- tetrahedra within the ceramics. Although the pure phase Na5Tm(MoO4)4 ceramic exhibited optimal dielectric properties (epsilon r=8.025, Qxf=18,967 GHz, and tau f = -101 ppm/degrees C) at 625 degrees C, the Na5Tm0.91Y0.03Yb0.06(MoO4)4 ceramic sintered at 600 degrees C demonstrated superior dielectric properties (epsilon r=7.82, Qxf=34,752 GHz, and tau f = -71.9 ppm/degrees C).