Preparation, Proton Transport Properties and Use in Gas Sensors of Thin Films of Zirconium Phosphate with γ-Layered Structure

Pellicular gamma-zirconium phosphate (gamma-ZP((p))), i.e. sheets made up entirely of oriented lamellae of Zr(PO(4))(H(2)PO(4))center dot 2H(2)O (gamma-ZP), have been obtained by filtering colloidal dispersions of exfoliated gamma-ZP in water/acetone. The ac-conductivity of gamma-ZP((p)) and gamma-ZP was measured in the temperature range 20/-20 degrees 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 gamma-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 gamma-ZP. Since the pellicular and microcrystalline material have very similar surface areas (11-12 m(2)/g), the higher conductivity of gamma-ZP((p)) is mainly due to the preferred particle orientation parallel to the electric field.