Postdeposition annealing induced transition from hexagonal Pr2O3 to cubic PrO2 films on Si(111)

Films of hexagonal praseodymium sesquioxide (h-Pr2O3) were deposited on Si(111) by molecular beam epitaxy and thereafter annealed in 1 atm oxygen at different temperatures, ranging from 100 to 700 degrees C. The films of the samples annealed at 300 degrees C or more were transformed to PrO2 with B-oriented Fm (3) over barm structure, while films annealed at lower temperatures kept the hexagonal structure. The films are composed of PrO2 and PrO2-delta species, which coexist laterally and are tetragonally distorted due to the interaction at the interface between oxide film and Si substrate. Compared to PrO2, PrO2-delta has the same cubic structure but with oxygen vacancies. The oxygen vacancies are partly ordered and increase the vertical lattice constant of the film, whereas the lateral lattice constant is almost identical for both species and on all samples. The latter lattice constant matches the lattice constant of the originally crystallized hexagonal praseodymium sesquioxide. That means that no long range reordering of the praseodymium atoms takes place during the phase transformation. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3152796]