Low-temperature fired thermal-stable Li2TiO3–NiO microwave dielectric ceramics

Abstract

Rock salt-structured (1 − x)Li2TiO3–xNiO (0 ≤ x≤0.5) solid solutions were prepared via a conventional solid-state method. The structure evolution, sintering behavior, and microwave dielectric properties were investigated systematically. The phase transition from an ordered monoclinic to a disordered cubic phase was observed as x increased from 0 to 0.4. Disordered cubic phases in x = 0.4–0.5 samples seemed to conform to the structure of LiTiO2 instead of Li2TiO3. The possible reason was ascribed to both the appearance of Ti3+ in the NiO-modified matrix and the lattice distortion from substituted ions with different radii. With a gradual decline of the structure order degree, τf was found to decrease from +26 to −36 ppm/°C. A greatly improved Q × f value of 103,050 GHz (at 7.65 GHz) could be yielded at x = 0.1 owing to the increased packing fraction. The 0.8Li2TiO3–0.2NiO ceramic exhibited excellent overall microwave dielectric properties of er = 20.4, Q × f = 83,608 GHz (at 7.63 GHz) and τf = 1.97 ppm/°C as sintered at 1250 °C. After the addition of 1 wt% BaCuB2O5, the x = 0.2 ceramic can be well densified at 850 °C and chemically compatible with pure silver, in addition to keeping superior properties of er = 19, Q × f = 62,252 GHz (at 7.84 GHz) and τf = −1.65 ppm/°C. All the above results indicate that the current material system would be a promising candidate for the application of low-temperature co-fired ceramics.