Tunable Microwave Dielectric Properties of the (Ba₁₋ₓSrₓ)Li₂Ti₆O₁₄ Ceramics and Effects of BCB Addition on Performance

Temperature-stable (Ba₁₋ₓSrₓ)Li₂Ti₆O₁₄ (0 ≤ x ≤ 1) microwave dielectric ceramics were synthesized using the solid-state reaction method. The influence of Sr incorporation on the crystal structure and microwave dielectric performance was systematically investigated. The findings show that adjusting the Sr ratio optimally leads to a notable improvement in the dielectric properties, resulting in a temperature coefficient of resonant frequency (τ_f) close to zero. Specifically, Ba₀.₂Sr₀.₈Li₂Ti₆O₁₄ demonstrates excellent microwave properties after sintering at 1025°C, exhibiting a permittivity (ε_r) of 26.2, a quality factor (Q × f) of 3,050 GHz (6.44 GHz), and a τ_f of −2.8 ppm/°C. Furthermore, the effect of incorporating 4 wt.% BaCu(B₂O₅) (BCB) on the grain growth and microwave dielectric properties was examined. The results demonstrate that BCB addition not only improves temperature stability but also significantly enhances the quality factor. The optimized microwave dielectric performance of Ba₀.₂Sr₀.₈Li₂Ti₆O₁₄ with 4 wt.% BCB were achieved at 850°C, yielding ε_r = 26.6, Q × f = 13,900 GHz at 6.62 GHz, and τ_f = +1.5 ppm/°C. Additionally, its compatibility with Ag electrodes indicates its suitability for low-temperature co-fired ceramic (LTCC)applications.