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 Li(3x)La(2/3-x)square(1/3-x)TiO(3) 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 degreesC. LLTO was obtained with an impurity : La2Ti2O7 in low proportions at 1200 degreesC. 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 degreesC and 34 mV/pH unit at 60 degreesC for the better responding electrode. The response is poor for material obtained at 800 and 1000 degreesC. 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 degreesC in buffer solutions. (C) 2004 Elsevier B.V. All rights reserved.