Abstract
Scanning probe microscopy measurements show irreversible surface electrochemistry in Sm-doped
CeO2 thin films, which depends on humidity, temperature and doping concentration. A
systematic study by electrochemical strain microscopy (ESM) in samples with two different
Sm content and in several working conditions allows disclosing the microscopic mechanism
underlying the difference in water adsorption and splitting with subsequent proton liberation.
We measure the behavior of the hysteresis loops by changing temperature and humidity, both
in standard ESM configuration and using the first order reversal curve (FORC) method.
Complementing our study with spectroscopic measurements by hard x-ray photoemission
spectroscopy we find that water incorporation is favored until the doping with Sm is too high
to allow the presence of Ce3+. The influence of doping on the surface reactivity and
conduction mechanism clearly emerges from all of our experimental results. We find that at
lower Sm concentration proton conduction is prevalent, featured by lower activation energy
and higher mobility. Defect concentrations determine the type of the prevalent charge carrier
in a doping dependent manner.
