论文信息 - Etudes structurales de compose´s de type ce´mentite: Effet de l'hydroge`ne sur Fe3C suivi par diffraction neutronique. Spectrome´trie Mo¨ssbauer sur FeCo2B et Co3B dope´s au57Fe

Etudes structurales de compose´s de type ce´mentite: Effet de l'hydroge`ne sur Fe3C suivi par diffraction neutronique. Spectrome´trie Mo¨ssbauer sur FeCo2B et Co3B dope´s au57Fe

Abstract Accurate neutron diffractograms obtained using Fe 3 C powdered samples have been recorded using position sensitive detectors. The structure parameters have been determined in the 20–650°C range both in vacuo and in hydrogen atmosphere. No significant location of hydrogen atoms in the cell could be detected before the complete decomposition of Fe 3 C, which is considerably enhanced by H 2 gas and is accompanied by an initial loss of carbon ( y axis: M (4 c ) ⋍ M(8f ) = 1.8 ± 0.1 μ B (extrapolated). Such a value agrees reasonably well with those obtained from Mo¨ssbauer data. Comparison with the isomorphous borides or Fe-substitutedCo 3 X compounds indicates that a rigid band model is inadequate to describe the electronic scheme of Fe in cementite and related compounds. Analysis of the stability of M 3 X cementite-type structured materials reveals the major role of M(d)-X(p) hybridization.

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