Effects of Ge4+ substitution on the crystal structure and microwave/terahertz dielectric properties of diopside ceramics

The rapid development of fifth/sixth-generation (5 G/6 G) telecommunication technologies has led to increased demands for silicate ceramic materials. In this work, Ge4+-substituted diopside, CaMg0.9Zn0.1Si2-xGexO6 (CMZSG, x = 0.0–2.0) ceramics were synthesized via the conventional solid-state method. All samples were sintered densely at 1200 ℃ for 4 h. CMZSG ceramics keep a single phase with C2/c and the lattice parameters vary smoothly with x. When 0.1 ≤ x ≤ 0.8, Ge4+ substitution prevents the abnormal grain growth. CMZSG ceramics have enhanced dielectric properties after substituting Ge4+, and the sample with x = 0.1 has the greatest dielectric properties with εr = 7.78 and Q×f = 190,300 GHz. The dielectric properties in the microwave and terahertz bands are compared, and the larger εr and Q×f values in the terahertz band are found due to the withdrawal of the partial polarization mechanism and different measurement methods. The relationship between lattice distortions and the dielectric properties is established. Both the local distortion in [Si/GeO4] tetrahedra chain and the distortion within [Si/GeO4] tetrahedron are found to contribute to the enhancement of Q×f values. Furthermore, the increased lattice expansion and the distortion within [Si/GeO4] tetrahedron contribute to a larger negative τf. These conclusions can guide us to design silicate ceramics with higher Q×f values and near-zero τf for application. The CaMg0.9Zn0.1Si1.9Ge0.1O6 ceramics exhibit excellent dielectric properties with εr = 7.48 and Q×f = 303,400 GHz in the terahertz band, rendering it a promising dielectric material for future terahertz mobile communication systems.