Fabrication of Temperature-Stable Low-Temperature Co-Fired Ceramics via Reaction Between Ba3(VO4)2 and Li2WO4

New glass-free low-temperature co-fired microwave dielectric composites with compositions (1-4x/3)Ba₃(VO₄)₂-xBaWO₄-(2x/3)Li₃VO₄ (x = 0.3-0.7) were fabricated by reactive liquid-phase sintering of (1-x)Ba₃(VO₄)₂-xLi₂WO₄ mixtures at 850 °C. During sintering, Li₂WO₄ is fully consumed by reacting with Ba₃(VO₄)₂ to form BaWO₄ and Li₃VO₄ while providing a transient liquid phase that promotes densification. As a result, the sintered ceramics achieve high relative densities of ≈94-98% at 850 °C. The relative fractions of Ba₃(VO₄)₂, BaWO₄, and Li₃VO₄ can be systematically tailored by adjusting the initial Li₂WO₄ content, enabling effective control of the temperature coefficient of the resonant frequency (τf) and the quality factor (<i>Q</i> × <i>f</i>). With increasing Li₂WO₄ content, the τf values shift from +23.97 to -45.48 ppm/°C, owing to the increasing contributions of the negative τf phases BaWO₄ and Li₃VO₄, while the <i>Q</i> × <i>f</i> values increase moderately from 44,300 to 47,300 GHz. The optimal microwave dielectric properties are obtained for x = 0.5, meaning εr = 9.19, <i>Q</i> × <i>f</i> = 45,900 GHz, and τf = -1.15 ppm/°C when sintering at 850 °C for 1 h. Chemical compatibility tests confirmed that the composites exhibit no detectable reaction with Ag electrodes, indicating that the Ba₃(VO₄)₂-BaWO₄-Li₃VO₄ system is a promising glass-free dielectric for LTCC applications requiring low firing temperature, near-zero thermal drift, and reliable electrode compatibility.