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The ZnZrNb 2 O 8 + x wt% LiF, MgF 2 , CuO (0.00 ≤ x ≤ 0.10), and Zn 1−x Cu x ZrNb 2 O 8 (0.000 ≤ x ≤ 0.050) ceramics were synthesized through solid-state reaction. Compared with pure ZnZrNb 2 O 8 ceramic, the quality factor and microstructure densification of the specimens with the addition of trace additives were significantly improved. When CuO was utilized as a sintering additive, 𝜀 𝑟 is mostly impacted by relative density, whereas Q × f value is primarily influenced by grain size. When CuO was employed as a dopant, 𝜀 𝑟 is strongly connected to the dielectric polarizability and lattice vibration, Q × f value is driven mostly by chemical bond covalency, and 𝜏 𝑓 value is primarily dictated by variations in Nb-O bond energy and bond valence. Notably, the ceramics demonstrated excellent characteristics (𝜀 𝑟 = 27.404, Q × f = 74 213 GHz, 𝜏 𝑓 = −52.779 ppm/ • C, ZnZrNb 2 O 8 + 0.06 wt% CuO; 𝜀 𝑟 = 27.448, Q × f = 72 520 GHz, 𝜏 𝑓 = − 53.143 ppm/ • C,Zn 0.997 Cu 0.003 ZrNb 2 O 8 ), and these make them promising for use in fifth generation communications.

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As a donor and acceptor separately, Nb 5+ and Al 3+ are used to substitute Ti 4+ in the ixiolite ZnTiNb 2 O 8 system for the first time. The dielectric responses in the terahertz range of this system are initially studied based on the data from terahertz time-domain transmitted spectroscopy. Combined with ligand field theory, the formation of a secondary phase of ZnAl 2 O 4 is reasonably explicated. Then, the origins of the lower dielectric loss and the terahertz wave absorption coefficient are determined to be the high chemical bond covalency and effective phase control. For the composition of ZnTi 0.85 (Al 0.5 Nb 0.5 ) 0.15 Nb 2 O 8 sintered at 1180°C, a low dielectric loss (<5 × 10 −3 @ 0.5 THz) and absorption coefficient (<10/cm @ 0.5 THz) are obtained, which make this kind of material propitious for developing terahertz dielectric devices. K E Y W O R D S complex chemical bond theory, covalency, dielectric properties, donor-acceptor substituted, microwave and terahertz

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