Microwave dielectric properties in the Li4+xTi5O12 (0 ≤ x ≤ 1.2) ceramics

Microwave dielectric ceramics, with a Li4+xTi5O12 (0 ≤ x ≤ 1.2) formula, were prepared using a conventional solid-state reaction method. The effects of doping amount on the phase stability, microstructure and microwave dielectric properties were investigated. The XRD analysis showed that at x = 0, pure Li4Ti5O12 could not be obtained but with trace amount of TiO2 as a secondary phase, while single phase of the Li4Ti5O12 solid solution was formed in x range of 0.2-0.4. The Li4Ti5O12 and Li2TiO3 coexisted in the compositions with 0.6 ≤ x ≤ 1.2 and the amount of Li2TiO3 phase increased with increasing doping concentration. The microwave dielectric properties were strongly dependent on the sintering temperature and composition. A near-zero τf of +2.7 ppm∕°C along with a Q × f of 36,000 GHz and a εr of 25.1 was obtained in x = 1.2 sample sintered at 1000 °C. Moreover, promising low temperature co-fired ceramic (LTCC) materials with thermal stability and chemical compatibility with silver can be obtained in the x = 1.2 sample with 0.5 wt% B2O3 addition sintered at 940 °C. This material has good microwave dielectric properties with εr of 28.0, Q × f of 32,000 GHz and τf of −7.8 ppm∕°C.