Low-temperature sintering and microwave dielectric properties of ZnGa_2–xO_4–1.5x ceramics with added B₂O₃

In this work, ZnGa_2–xO_4–1.5x (0.0 ≤ x ≤ 0.15) ceramics were synthesized by a solid-state reaction method. ZnGa₂O₄ ceramic that is sintered at 1300 °C/3 h exhibits good microwave dielectric properties with ε_r of 11.06, Q × f of 74,730 GHz, and τ_f of − 69.7 ppm/°C. However, it cannot be fully densified at temperatures lower than 960 °C, even when a large amount of B₂O₃ is added, which seriously inhibits its application in the LTCC (low temperature cofired ceramic) field. Therefore, adding B₂O₃ to Ga₂O₃-deficient ZnGa₂O₄ ceramics is proposed to decrease the sintering temperature to below 960 °C. Owing to the dual effect of the B₂O₃-rich and ZnO-B₂O₃ related liquid phases, ceramics with added B₂O₃ (≥ 20 mol%) were found to sinter well at 950 °C, and good microwave dielectric properties were also achieved. In particular, 25 mol% B₂O₃ added to ZnGa_1.95O_3.925 ceramic sintered at 950 °C showed promising microwave dielectric properties for 5 G/6 G technologies without reaction with a silver electrode: ε_r = 9.19, Q × f = 37,337 GHz, and τ_f = − 58.3 ppm/°C.