Optical-vibration and intrinsic dielectric properties of low-k high-Q Zn2GeO4 ceramics

Abstract

Polycrystalline Zn2GeO4 powders and sintered ceramics were prepared by the microwave–assisted solid-state reaction method. Structural, chemical, and morphological properties, as well as the optical-vibration features of the obtained materials, were investigated by XRD, scanning and transmission electron microscopies, polarized micro-Raman scattering, and infrared spectroscopy. Single-phase, high-purity, crystalline powders and ceramics belonging to the rhombohedral R3‾ space group showed excellent polarized Raman response, which allowed us to determine and assign 39 gerade phonons out of the 42 optical modes predicted for Zn2GeO4 by group theory. Also, the 29 most relevant polar phonons (ungerade) of the sintered material were revealed and the dielectric strengths of the modes that contribute to the dielectric response were obtained. The infrared dispersion parameters allowed us to calculate the extrapolated dielectric constants ε0 = 7.02 and ε∞ = 2.41, and an intrinsic quality factor Qu × f = 187 THz, at 10 GHz, values that are quite suitable for applications as low-k high-Q materials in microwave circuitry. The very comprehensive set of phonon modes obtained here should be useful for understanding the behavior of the material, needed to improve their already numerous optical applications (luminescence, photocatalysis).