La5.5WO12-δ Characterization of Transport Properties under Oxidizing Conditions: A Conductivity Relaxation Study

The conduction properties of La5.5WO12-δ have been studied by using the electrochemical conductivity relaxation technique. Exchange and diffusion coefficients have been obtained from relaxation experiments including measurements of conductivity transients from (1) oxidation–reduction under dry and wet oxygen and (2) hydration–dehydration for both H2O-saturated and D2O-saturated oxygen at atmospheric pressure. The evolution of the total conductivity as a function of temperature, oxygen partial pressure, and the presence of H2O or D2O has moreover been characterized. The exchange coefficient for oxygen and water incorporation was calculated from the relaxation experiments. It was also possible to determine the coefficients for oxygen vacancy/oxygen ion (in dry and hydrated state) diffusion and for ambipolar diffusion of water. Oxygen vacancy/oxide ion diffusion is apparently not affected by the hydration state within the studied temperature range and water and oxygen partial pressures. The ambipolar water diffusion coefficient was significantly smaller than the one for the oxygen ion.