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Varshney, Dinesh; Yogi, Arvind
Journal of molecular structure, 05/2011, Volume: 995, Issue: 1-3Journal Article
We investigate the structural and transport properties of Mn doped hematite ( alpha -Fe sub(2O) sub(3)). The X-ray diffraction pattern identifies the single-phase and corundum (Al sub(2O) sub(3)) type structure of the polycrystalline samples Fe sub(2-) sub(x)Mn sub(xO) sub(3) (x = 0, 0.01, 0.10 and 0.50). The resistivity curve shows a Morin transition (T sub(M) in hematite ( alpha -Fe) sub(2)O sub(3) at about 262 K. As the Mn-content increases in the solid solution of hematite ( alpha -Fe) sub(2)O sub(3), the number of pairs of (Fesuper2+, Fesuper3+) and (Mnsuper2+, Mnsuper3+) in the solid solution increases which changes the conductivity of the solid solution. The Mn doping influences the Morin transition and T) sub(M) shifts towards lower temperatures on enhanced doping. For higher doping, T sub(M is further suppressed significantly. The Raman measurements of alpha -Fe) sub(2)O sub(3 samples shows seven Raman active modes at A) sub(1) sub(g(1) inline image 225 cmsuper-1, E) sub(g)(1) inline image 249 cmsuper-1, E sub(g(2) inline image 292 cmsuper-1, E) sub(g)(3) inline image 297 cmsuper-1, E sub(g(4) inline image 409 cmsuper-1, E) sub(g)(5) inline image 496 cmsuper-1, and A sub(1) sub(g)(2) inline image 609 cmsuper-1. Moessbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields clearly show the presence of ferric (Fesuper3+) state and strong magnetic ordering in all samples. Fe sub(2-) sub(x)Mn sub(xO) sub(4) hematites are in single phase and possess corundum type structure. Resistivity data shows Morin transition for parent -Fe sub(2O) sub(3) observed at T sub(M 262 K. Mn doping influences Morin transition and T) sub(M) shifts towards lower temperatures. Seven Raman active modes are identified for Mnsuper2+ doped Fe sub(2-) sub(x)Mn sub(xO) sub(4) hematites. Room temperature Moessbauer spectrum confirms +3 oxidation state of Fe as ferric.
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