M?ssbauer studies of the phase composition and microstructure of the La1-xCaxFeO3-y system as related to the reactivity of surface and bulk oxygen |
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Authors: | LA Isupova IS Yakovleva II Gainutdinov YuT Pavlyukhin and VA Sadykov |
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Institution: | (1) Boreskov Institute of Catalysis, Novosibirsk, 630090, Russia;(2) Institute of Solid State Chemistry Kutateladze st., 18, Novosibirsk, 630090, Russia |
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Abstract: | The phase composition and microstructure of samples of the La1-xCaxFeO3-y system prepared via a ceramic route were characterized by M?ssbauer spectroscopy. In all cases, iron was found in the 3+ state. The ordering
of anion vacancies in the samples with the composition in the range of 0.8 > x ≥ 0.4, which corresponds to a microheterogeneous
solid solution, generates new distorted octahedral and fivefold/tetrahedral sites revealed by two typical sextets. The disordering
of this solid solution and small (10-100 ?) sizes of domains with a perovskite, braunmillerite or Grenier phase structure
caused the appearance of a superparamagnetic doublet, which grows with the Ca content up to x = 0.8 but disappears in the
sample of pure braunmillerite. The appearance of Fe cations in a distorted coordination correlates with the increased activity
of the samples with a microheterogeneous structure in the CO catalytic oxidation and with their reducibility by H2.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | Calcium-doped lanthanum ferrite M?ssbauer spectroscopy |
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