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 (Q × f). 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 Q × f 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, Q × f = 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.