Phase transformations in reduced ceria: Determination by thermal expansion measurements

Phase transitions in reduced ceria (CeO2−x) due to solid-state reactions yield a complex phase diagram. Associated with these transformations is a change in molar volume of the sample. For certain mixtures of coexisting phases internal stress develops and the sample is not in true equilibrium. As a result, the molar volume of the phase under pressure is reduced. Experimental and theoretical evaluations confirm the phase diagram determined before by specific heat measurements. New data collected concerning the local pressure effect enabled the development of a more detailed explanation of this deviation from equilibrium.