Low-Temperature Sintering and Microwave Dielectric Properties of CuxZn1−xTi0.2Zr0.8Nb2O8 Ceramics with the Aid of LiF

<i>M</i>²⁺<i>N</i>⁴⁺Nb₂O₈-type ceramics (where <i>M</i> = Mg, Ca, Mn, Co, Ni, Zn and <i>N</i> = Ti, Zr) are essential for satellite communication and mobile base stations due to their medium relative permittivity (<i>ε</i>_r) and high quality factor (<i>Q</i> × <i>f</i>). Although ZnTi_0.2Zr_0.8Nb₂O₈ ceramic exhibits impressive microwave dielectric properties, including an <i>ε_r</i> of 29.75, a <i>Q</i> × <i>f</i> of 107,303 GHz, and a <i>τ_f</i> of -24.41 ppm/°C, its sintering temperature of 1150 °C remains a significant barrier for integration into low-temperature co-fired ceramic (LTCC) technologies. To overcome this limitation, a strategy involving the partial substitution of Zn²⁺ with Cu²⁺ and the addition of LiF as a sintering aid was devised for ZnTi_0.2Zr_0.8Nb₂O₈. The dual impact of Cu²⁺ partial substitution and LiF as a sintering enhancer facilitated the successful sintering of Cu_0.3Zn_0.7Ti_0.2Zr_0.8Nb₂O₈ ceramics at a reduced temperature of 950 °C using the conventional solid-state reaction method. These ceramics exhibited excellent microwave dielectric properties. Notably, Cu_0.3Zn_0.7Ti_0.2Zr_0.8Nb₂O₈ ceramic with 40 mol% LiF addition demonstrated optimal microwave dielectric properties without any reaction with a silver electrode at a sintering temperature of 950 °C, yielding <i>ε_r</i> = 32, <i>Q</i> × <i>f</i> = 45,543 GHz, and <i>τ_f</i> = -43.5 ppm/°C.