Microwave dielectric properties and low-temperature sintering of (1-x)BaTi₄O₉-xBaMoO₄ composite ceramics

Low-temperature co-fired ceramics (LTCC) technology is a promising solution for achieving miniaturization and integration in microwave devices. In this study, a novel series of (1-x)BaTi₄O₉-xBaMoO₄ (x = 0.1, 0.2, 0.3, and 0.4) ceramics were synthesized via solid-state reaction. Orthorhombic BaTi₄O₉ phase and tetragonal BaMoO₄ phase coexist in the (1-x)BaTi₄O₉-xBaMoO₄ composite system. The 0.6BaTi₄O₉-0.4BaMoO₄ composition sintered at 1260 °C for 4 h demonstrated optimal microwave dielectric properties: a relative permittivity (ε_r) of ∼26.8, a high Q×f value of ∼50,100 GHz (at 7.24 GHz), and a near-zero temperature coefficient of resonant frequency (τ_f) of + 3.7 ppm/°C. Remarkably, the sintering temperature of the 0.6BaTi₄O₉-0.4BaMoO₄ ceramics was significantly reduced from 1260 °C to 920 °C by incorporating 3 wt% BaCu(B₂O₅) additive, while maintaining excellent performance (ε_r ∼ 26.1, Q×f ∼ 27,900 GHz at 7.32 GHz, τ_f ∼ +6.3 ppm/°C). Furthermore, it exhibited excellent chemical compatibility with Ag electrodes, confirming its potential as a candidate material for LTCC microwave applications.