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Well-crystallized kaolinite was found to exhibit marked proton conductivity at pre-dehydration temperatures. Direct current conductivity and thermopotential measurements were performed. By comparing the results obtained with Au electrodes (proton blocking) to those obtained with Pd electrodes (proton injecting), non-protonic contributions could be separated from proton conductivity. The majority charge carriers appeared to be defect proton (negative sign), corresponding chemically to an 02 replacing OH-in the lattice, but excess protons were also noted (positive sign). Below 275~ the activation energy was of the order of 7-8 kcal mole-l; between 275-450~ it was about 18 20 kcal mole -t. This indicated a two-step defect proton-excess proton conductivity mechanism involving, in succession, the two kinds of OH -in the kaolinite structure: (i) OH-located within the six-membered ring formed by the SiO4 tetrahedral sheet, (ii) the close OH-array formed by the octahedral sheet. The conductivity results were supported by IR spectroscopic measurements.

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