Investigation of the manganite CaMn7O12 through Fe-57 probe Mossbauer spectroscopy in two different temperature domainsстатья
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Аннотация:Mossbauer studies of Fe-57-doped CaMn7O12 have been carried out over two paramagnetic ranges of temperature. The observed hyperfine parameters of Fe-57 spectra were discussed assuming that Fe3+ cations are mainly substituted for manganese cations in six-coordinated oxygen polyhedra. In the first temperature range 90 K < T < 380 K, the values of quadrupole splitting (Delta(1)>> Delta(2)) are evidence for two types of structural distortion of (MnO6) polyhedra due to the ordering of Mn3+ and Mn4+ cations in (9d) and (3b) sites of a trigonal structure with a charge ordering. In the second temperature range 380 K < T < 460 K, the observed temperature evolution of the line shape in Fe-57 spectra confirms two phenomena: (i) the structural phase transition of the trigonal phase to a high-temperature cubic structure, with the coexistence of both phases between 380 and 450 K; (ii) the existence of only non-distorted (MnO6) octahedra due to the fast electronic exchange between Mn3+ and Mn4+ cations. (c) 2007 Elsevier Ltd. All rights reserved.