High-resolution transmission electron microscopy, electron energy-loss spectroscopy, and electron diffraction were used to study the microstructure of epitaxial La0.5Sr0.5CoO3–θ thin films grown on (001) oriented LaAlO3 substrates. Films were characterized before and after annealing treatments under different O partial pressures. Electron energy-loss spectroscopy showed that annealing reduced the valence state of Co due to loss of O. High-resolution transmission electron microscopic image simulations showed that the superstructure contrast observed could be explained by shifts of cations in planes containing ordered O vacancies. The as-deposited film showed weak, short-range ordering of O vacancies within nanometer-sized domains. The annealed film showed long-range order and a strong anisotropy in ordering, with the O-deficient planes aligned parallel to the film/substrate interface. It was proposed that the anisotropy in ordering was a mechanism of stress relief in these films.

Oxygen Vacancy Ordering in Epitaxial La0.5Sr0.5CoO3–θ Thin Films on (001) LaAlO3. S.Stemmer, A.J.Jacobson, X.Chen, A.Ignatiev: Journal of Applied Physics, 2001, 90[7], 3319-24