Modeling of X-ray Diffraction Patterns from Nanostructured Perovskites Sr(Fe,Co)О3–δ
U. V. ANCHAROVA1, S. V. CHEREPANOVA2 and N. Z. LYAKHOV1
1 Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of the Russian Academy of Sciences, Ul. Kutateladze 18, Novosibirsk 630128 (Russia)
2 Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Pr. Akademika Lavrentyeva 5, Novosibirsk 630090 (Russia)
ancharova@gmail.com
Keywords: nanostructuring, perovskite, defects in crystals, synchrotron radiation, diffraction simulation
Pages: 351–359
Abstract
Different models of defect ordering in strongly nonstoichiometric perovskite-like oxides based on strontium ferrites/cobaltites Sr(Co0.8Fe0.2)O3–δ, (Sr0.7La0.3)(Co0.5Al0.3Fe0.2)O3–δ, (Sr0.7Сa0.3)(Co0.5Al0.3Fe0.2)O3–δ, Sr(Co0.75Nb0.05Fe0.2)O3–δ, Sr(Co0.7Nb0.1Fe0.2)O3–δ and Sr(Fe0.95Mo0.05)O3–δ (2.5 < (3–δ) < 2.7) are considered. Diffraction patterns of a number of samples differing in cation composition and degree of nonstoichiometry exhibit intensive reflections that are characteristic of the perovskite structural type with weak wider superstructural peaks. It is demonstrated by means of computer modelling of X-ray scattering on the crystals with different defects that such a diffraction pattern can correspond to three models of ordering of the oxygen vacancies: the formation of a homogeneous structure with the ordered state of oxygen vacancies (structural elements of the low-symmetry phase) and the formation of nano-heterogeneous systems (brownmillerite ABO2.5 + perovskite ABO3) of two types. In the first case, the components of the system have lamellar shape and interchange in one direction (a unidimensional disorder). In the second case we speak of the structure of brownmillerite domains turned with respect to each other at an angle of 90°, with different methods of redistribution of the perovskite component – at interfaces or in the form of separate domains. It is demonstrated with the help of two-dimensional diffraction of X-rays that this texture is observed not only at the nano-level but also for the samples with microdomains.
|
