V2O5-Assisted Low-Temperature Sintering and Microwave Dielectric Properties of (1 − x)Li2.08TiO3–xLi2ZnTi3O8 (x = 0.3−0.7) Ceramics for LTCC Applications

A new composite microwave-dielectric system, (1 - x)Li_2.08TiO₃-xLi₂ZnTi₃O₈ (x = 0.3-0.7), was systematically investigated to identify the optimal composition for low-temperature co-fired ceramic (LTCC) applications by correlating sintering behavior, microstructural evolution, and microwave-dielectric properties. Although the undoped compositions exhibited excellent intrinsic dielectric performance, they required sintering at 1100 °C, making them incompatible with Ag-based LTCC processing. Among the investigated formulations, 0.6Li_2.08TiO₃-0.4Li₂ZnTi₃O₈ was identified as the most suitable base composition. To reduce the sintering temperature, 0.3-1.0 wt.% V₂O₅ was introduced as a sintering aid, enabling densification at 900 °C for 30 min (97.0% relative density) while preserving the coexistence of Li_2.08TiO₃ and Li₂ZnTi₃O₈ without XRD-detectable secondary phases. Microstructural observations indicated that V₂O₅ promoted liquid-phase sintering, leading to enhanced densification and Li_2.08TiO₃-selective abnormal grain coarsening without altering the intrinsic permittivity. Complementary dilatometry provided process-level evidence for this liquid-phase sintering mechanism: large total shrinkage at 900 °C (∆L/Lo≈ -17-19%), earlier Tonset/Tpeak with Tpeak lowered by ~250 °C, and an increased Rpeak, collectively supporting 900 °C/30 min as the practical firing window. The optimized 0.6Li_2.08TiO₃-0.4Li₂ZnTi₃O₈ composition containing 0.3 wt.% V₂O₅ exhibits excellent microwave-dielectric properties (εr = 23.32, <i>Q × f</i> = 68,400 GHz, and τf = -1.55 ppm/°C). Higher V₂O₅ contents (>0.3 wt.%) caused a gradual reduction in <i>Q × f</i> due to increasing microstructural non-uniformity. Ag co-firing tests confirmed electrode stability with no interfacial reactions at 900 °C for 30 min. Overall, 0.3 wt.% V₂O₅-assisted 0.6Li_2.08TiO₃-0.4Li₂ZnTi₃O₈ provides a practical sub-950 °C processing window that satisfies key LTCC requirements, including moderate permittivity, high <i>Q × f</i>, near-zero τf, and compatibility with Ag electrodes.