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I. A. Presniakov, K. V. Pokholok, A. V. Sobolev
119Sn
mossbauer probe atoms in antiferromagnetic ferrites with a brownmillerite-type
structure
Abstract
Mossbauer spectroscopy has been for studying local
environment of 119Sn probe atoms within tin-doped A2Fe2O5 (A = Ca,
Sr) ferrites with brownmillerite-type structure. In the case of Ca2Fe2O5, the 119Sn spectra
recorded below the magnetic ordering temperature (TN) indicate that
Sn4+ dopant ions are located in sublattice with
octahedral oxygen surrounding. On the contrary, the 119Sn spectra of the
Sr2Fe2O5 ferrite can be
described as a superposition of two Zeeman sextets, which indicate that Sn4+ dopant ions are
located in two non-equivalent crystallographic and magnetic sites. The observed
hyperfine parameters were discussed supposing Sn4+ ions being
stabilized in the tetrahedral sublattice complete their nearest oxygen
surrounding up to the octahedral oxygen coordination. Annealing of the
tin-doped Sr2Fe2O5 simple in helium
flux condition leads to formation of divalent Sn2+ ions with a
simultaneous decrease of the contribution for 119Sn4+ sub-spectrum.
The hyperfine parameters of 119Sn2+ sub-spectrum
underline that impurity atoms are stabilized in the sp3d – hybrid state
in the oxygen distorted tetragonal pyramid. The analysis of the 119Sn spectra
indicates a chemical reversibility of the processes Sn2+ " Sn4+ within the
tetrahedral sublattice of the brownmillerite-type ferrite.
Copyright (C) Chemistry Dept., Moscow State University, 2002
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