Novel single-phase Li2SiO3 microwave dielectric ceramic with low permittivity

Abstract

Novel low-permittivity lithium metasilicate (Li₂SiO₃) ceramics were synthesized to explore the relationships between crystal structure parameters and dielectric properties. X-ray diffraction and Rietveld refinement indicated that the Li₂SiO₃ ceramics formed a single orthorhombic structure with a Cmc2₁ space group. Optimal microwave dielectric properties of ε_r = 6.20 ± 0.02, Q×f = 30,550 ± 250 GHz (f₀ = 15.5 GHz), and τ_f = −40.95 ± 0.56 ppm/℃ were achieved through sintering at 1025 ℃. Raman spectroscopy analysis showed that the values of ε_r and Q×f were negatively correlated with the Raman shift and full width at half maximum of the strongest peak at 982 cm⁻¹, respectively. Meanwhile, the Phillips–Vechten–Levine theory revealed that the ε_r values and the Q×f values were closely related to the average bond ionicity and the lattice energy of the Si-O bonds, respectively. Moreover, the increase in τ_f values depended on the increase in oxygen bond valence and the distortion of the [LiO₄] tetrahedron. These results on the Li₂SiO₃ ceramics could provide some theoretical information for developing high-performance microwave dielectric ceramics.