Synthesis of the perovskite ceramic Li3xLa2/3–xTiO3 by a chemical solution route using a triblock copolymer surfactant
Journal of Sol-Gel Science and Technology, Volume 46, Number 2 / May, 2008, 137-145
Thi Ngoc Ha Le, Mickaël Roffat, Quoc Nghi Pham, Stéphanie Kodjikian, Odile Bohnke and Claude Bohnke
Abstract: The synthesis of the perovskite Li3xLa2/3–x□1/3–2xTiO3 by a chemical solution route, using a triblock copolymer surfactant, PEOn–PPOm–PEOn, is described. This titanate is a non-hygroscopic fast lithium conductor and therefore is a good candidate for electrochemical applications. It is generally prepared by a conventional solid-state reaction (SSR) method. However this synthesis method does not allow the preparation of nanopowders or the formation of thin films. For these special purposes, synthesis by a chemical solution route, with the formation of a polymeric precursor during synthesis, has been investigated. By using the above-mentioned non-ionic surfactant, the preparation of nanopowders of complex oxides can be done. Furthermore, this way of synthesis leads to the formation of an intermediate polymeric precursor which can be easily spread on substrates to obtain films. We show that the formation of a pure phase of the perovskite Li3xLa2/3–x□1/3–2xTiO3 is highly dependent on the synthesis conditions, namely the presence of water in the solvent, the EO/metal ratio, the Li+ content in the precursor and the calcination temperature. The influence of these parameters on the microstructure of the oxide is studied by X-ray diffraction, scanning electron microscopy and granulometry. A powder of Li3xLa2/3–x□1/3–2xTiO3 (x = 0.10), with an average particles size of 200 nm, has been obtained. The ionic conductivity of this oxide is the same as the one obtained with oxide prepared by SSR (a bulk conductivity of 1.4 × 10−3 S/cm at 37 °C). The ceramic obtained from this powder after sintering at 1,150 °C shows a good pH response. This material can then be used as a sensitive membrane in a potentiometric pH sensor. The presence of hydrophobic PPO groups in the polymer precursor allowed preparing films of Li3xLa2/3–x□1/3–2xTiO3 with a good adherence on Pt substrate. This kind of synthesis is then very promising to prepare micro pH sensors.