A Comprehensive Study on the BaCu_2–xSi₂O_7–x (0 ≤ x ≤ 1) Ceramics with Low Sintering Temperature and Applications in Dielectric Resonant Antenna

Based on the ternary phase diagram of BaO–CuO–SiO₂, a series of BaCu_2–xSi₂O_7–x (0 ≤ x ≤ 1) samples were prepared by using the conventional solid-state reaction method. By adjusting the Cu content, the phase composition between BaCu₂Si₂O₇ and BaCuSi₂O₆ was effectively controlled. These two phases can coexist stably in the sintering temperature range of 1000–1060 °C. This two-phase coexistence state enhances the densification of ceramics. At x = 0.5 and sintered at 1020 °C, the sample exhibited optimal microwave dielectric properties, with a relative dielectric constant (ε_r) of approximately 8.07. Its Q × f (where Q is the quality factor and f is the resonant frequency) is as high as 47,200 GHz, and the resonant frequency temperature coefficient (τ_f) is −20.00 ppm/°C. When x = 0.5, adding 1 wt % BaCu(B₂O₅) (BCB) and 1 wt % LBSCA glass additives significantly reduce the sintering temperature to 890 °C. The samples still exhibit competitive microwave dielectric properties (ε_r ≈ 7.8, Q × f ≈ 19,900 GHz, τ_f ≈ −19.00 ppm/°C), along with excellent chemical compatibility with silver electrodes. These findings demonstrate that BaCu_2–xSi₂O_7–x ceramics are promising candidates for low-temperature cofired ceramics technology (LTCC) applications.