Microwave/terahertz dielectric properties of high-Q willemite ceramics: Dual control through non-stoichiometric design and Ge4+ substitution

The advancement of communication technologies demands dielectric materials with superior performance characteristics, particularly low permittivity and minimal dielectric loss. This study investigates Ge 4+ -substituted willemite ceramics, including Zn 2 Si 1– x Ge x O 4 (ZS- x Ge, x = 0 and 0.1) and Zn 1.8 Si 1– y Ge y O 3.8 (ZS- y Ge, y = 0 to 0.3), synthesized via the conventional solid-state method. The non-stoichiometric design effectively suppresses the formation of ZnO. The intrinsic and extrinsic losses of the ZS- x Ge ceramics are separated by a systematic comparative analysis of the dielectric losses in the terahertz band, and the extrinsic losses are fitted by the Drude term in the Lorentz-Drude dielectric response model. Consequently, ZS- y Ge ceramics exhibit lower ε r and significantly improved Q × f values across microwave to terahertz band. In ZnO-free ceramics, Ge 4+ substitution enhances the ionic polarizability, the unit cell volume and the bond strain, increasing ε r and Q × f values (decreasing intrinsic losses), and decreasing τ f . The optimized Zn 1.8 Si 0.9 Ge 0.1 O 3.8 ceramics demonstrate superior dielectric properties with ε r = 6.66, Q × f = 225,500 GHz and τ f = –60.0×10 −6 °C –1 at 12.45 GHz, and ε r = 7.02, Q × f = 401,800 GHz at 1 THz. These novel ceramics are positioned as promising candidates for next-generation microwave and terahertz communication devices.