Synthesis of Li_2.06Nb_0.18Ti_0.76O₃ powder at low temperature via the sol-gel process

Lithiumtitanate solid solution (Li_2.06Nb_0.18Ti_0.76O₃) powder was successfully synthesized via the sol-gel process. By using Nb₂O₅, LiOH·H₂O and Ti(C₄H₉O)₄ as the raw materials, and citric acid as the complexing agent, transparent sol was formed by controlling pH values and temperatures. The single-phase of Li₂TiO₃ solid solution was obtained at 700°C using a chemical method, which is 150°C lower than the temperatures used in the traditional solid-phase synthesis method. The infrared spectroscopy, X-ray diffraction and scanning electron microscope (SEM) were applied in the characterization of the citrate precursor and the as-obtained powder. The phase transition process was studied in detail and a plausible evolution mechanism of the chemical processed powder in the calcination process was proposed. Results show that during the calcination process, some metastable phases such as the anatase TiO₂ phase and M-phase are formed as well as the Li₂TiO₃ solid solution phase. As the temperature rises, all the metastable phases disappear and pure Li₂TiO₃ solid solution phase is obtained. The SEM image reveals that the Li₂TiO₃ solid solution is composed of rod-like and square block particles. The sintering, microstructure and dielectric properties were investigated on the different samples prepared by the sol-gel and solid state methods. The results show that the former presents a special microstructure and reaches the maximum bulk density at low temperatures. The samples as-obtained by the sol-gel method have a lower dielectric constant and dielectric loss at the same frequency as compared to ones prepared by the solid state method.