Room temperature phase transition in CeO2 nanocrystalline films

The temporal evolution of the lattice parameter of oxygen deficient nanocrystalline cerium oxide films was monitored by X-ray diffraction. It was found that films with lattice parameter of approximate to5.47 Angstrom upon deposition undergo large spontaneous expansion, in which the size of the unit cell increases by approximate to0.7% during the course of days. The films with as-deposited lattice parameter larger or smaller than approximate to5.47 Angstrom do not show significant changes. This behavior is consistent with the previously suggested hypothesis of an order-disorder transition of oxygen vacancies and can be viewed as its direct experimental confirmation.