Preparation, proton transport properties and use in gas sensors of thin films of zirconium phosphate with γ-layered structure
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Pellicular γ-zirconium phosphate (γ-ZP(p)), i.e. sheets made up entirely of oriented lamellae of Zr(PO4)(H2PO4)·2H2O (γ-ZP), have been obtained by filtering colloidal dispersions of exfoliated γ-ZP in water/acetone. The ac-conductivity of γ-ZP(p) and γ-ZP was measured in the temperature range 20/–20°C on samples previously conditioned at relative humidities between 90 and 5%. In both cases, the conductivity dependence on material hydration indicates the presence of a non-negligible bulk transport at low relative humidities. For each relative humidity the conductivity data have been parameterised on the basis of the Arrhenius equation. Activation energy and pre-exponential factor values suggest the presence of the same conduction mechanism in both materials. The conductivity of γ-ZP(p) measured by applying the electric field parallel to the sheets ranges from 3·10−4 to 1·10−5 S cm−1 for relative humidity decreasing from 90 to 11%, being an order of magnitude higher than that of γ-ZP. Since the pellicular and microcrystalline material have very similar surface areas (11–12 m2/g), the higher conductivity of γ-ZP(p) is mainly due to the preferred particle orientation parallel to the electric field.
KeywordsRelative Humidity Arrhenius Equation Colloidal Dispersion Proton Transport Field Parallel
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