Peculiarities of Li_0.5La_0.5TiO₃ Formation during the Synthesis by Solid-State Reaction or Precipitation from Solutions

It is shown that whatever the technique used, conventional solid-state reaction or precipitation from solutions, the formation of lithium lanthanum titanate, Li 0.5 La 0.5 TiO 3, is a multistage process, which occurs in a wide temperature range. Thermal analyses, X-ray powder diffraction (XRPD), and infrared (IR) spectroscopy are used to investigate the phase transformations that occur during the preparation of these ceramics. The different steps involved in the mechanism of formation of this titanate are described as temperature is increased. Both techniques lead to a pure perovskite phase. However, synthesis from solutions allows one to produce nanosized powders of titanate phase and to carry out synthesis under milder conditions as compared with solid state reaction synthesis. Furthermore, it has been observed that, independently of the method used, a considerable loss of lithium occurs during the synthesis of the ceramic samples and that the real composition is Li 0.41 La 0.5 TiO 2.955 for both ceramics. The conductivity of these ceramics has been investigated by ac impedance spectroscopy. It is shown that the ceramic samples, obtained after sintering around 1300 °C, display identical conductivity value, either for the bulk or for the grain boundary. This result is due to the close ceramic grain size obtained after sintering, as shown by scanning electron microscopy (SEM) experiments.