Electronic transport in single crystals of Gd-doped ceria

In this work we study the electronic conductivity of reduced Gd-doped ceria in single crystals by impedance spectroscopy in the near-room-temperature regime (25-110 degrees C). The extent of nonstoichiometry in the as-prepared reduced samples is determined by thermogravimetry and the integral enthalpy of reoxidation by differential scanning calorimetry. The results indicate that the electronic transport takes place via small polarons as in the case of pure ceria. We estimate the activation energy for the process of conduction to be 0.44 eV for Ce0.8Gd0.2O1.864 and 0.45 eV for Ce0.7Gd0.3O1.82. We found that trapping takes place at the near-room-temperature regime with a considerable entropic contribution. The integral enthalpy of reoxidation for Ce0.8Gd0.2O1.864 is 4.2 eV and for Ce0.7Gd0.3O1.82 is 3.6 eV. (c) 2007 The Electrochemical Society.