Spontaneous stress-induced oxidation of Ce ions in Gd-doped ceria at room temperature

Cerium oxides are widely used within catalysis and fuel cells. The key parameters of interest, including catalytic activity, transport properties and defect structure are all fundamentally linked to the oxidation state of the cerium ions within the material which can adopt a 3+ or 4+ oxidation state. We use Raman spectroscopy, as well as scanning and optical microscopy to show that the oxidation state of cerium ions within Ce0.8Gd0.2O2-x can be altered either through chemically induced strain (imparted during processing), mechanical indentation, fracture or applied mechanical load. This work shows that both the chemical environment and stress state will play a role in determining the oxidation state of the cerium ions within ceria containing materials. It has been shown that the rate of oxidation of Ce0.8Gd0.2O2-x can be dramatically altered at room temperature via changing the local stress state of the material.