Comparison of pH sensitivity of lithium lanthanum titanate obtained by sol–gel synthesis and solid state chemistry

The use of the high lithium-conductive perovskite compound Li3xLa2/3−x 1/3−xTiO3 for the detection of H+ species in aqueous solution was investigated. The compound was synthetized by the sol–gel route and heat treatments at temperature between 800 and 1200 °C. LLTO was obtained with an impurity : La2Ti2O7 in low proportions at 1200 °C. After sintering, the ceramics were used in a pH sensitive electrode and studied by Scanning Electron Microscopy. A variation of potential in different pH-buffers was obtained with a response maximum of 28 mV/pH unit at 25 °C and 34 mV/pH unit at 60 °C for the better responding electrode. The response is poor for material obtained at 800 and 1000 °C. A comparison with the properties of the same material obtained by solid state reaction and after ball-milling and sintering is shown. The membrane configuration proves the ability of this perovskite to detect the variation of pH between 2 and 10. The response is not Nernstian but the sensitivity and the response time are good. The origin of the detection seems linked to a surface reaction. The detection inhibited when the electrodes are stocked in air can be retrieved by heating at temperatures higher than 40 °C in buffer solutions.