Water adsorption at the surface of pure and Gd-doped ceria

The presence of water at the surface of sputtered thin films of Ce0.8Gd0.2O1.9, which display elastic anomalies as a function of thermal treatment, and of stoichiometric CeO2 films, which do not, was monitored using X-ray photoelectron spectroscopy. We find that considerably more water is strongly bound at the surface of the Ce0.8Gd0.2O1.9 films than of the CeO2 films. This supports the theoretical prediction that water binds preferentially at the oxygen vacancy sites. In addition, all films were treated according to the protocol which has been shown to produce inelastic behavior in the doped films: annealed at 500 °C, exposed to ambient atmosphere for one month and then heated to 250 °C in ultra-high vacuum. Neither the Ce0.8Gd0.2O1.9 nor the CeO2 films show any change in the amount of adsorbed water. We therefore conclude that changes in the amount of surface adsorbed water do not play a role in the elastic anomalies observed as a function of thermal treatment of Ce0.8Gd0.2O1.9 films.