Abstract.
Mössbauer spectroscopy has been used to systemically study the catalytic mechanism of Fe-based alloys in diamond formation at high temperature–high pressure (HTHP) for the first time. Mössbauer spectra reveal the magnetic state of the 3d electrons of a Fe atom in the Fe-based alloy catalyst during diamond formation at HTHP. During carburization at lower temperatures than that required for diamond formation and diamond formation in the diamond-stability region using Fe-based alloys as a catalyst, both the quadrupole splitting QS and the isomer shift IS change from negative to positive, especially reaching a state in which they are zero. It was indicated that the state of the 3d-shell electrons of the iron atom changes greatly during carburization and diamond formation and that the incomplete 3d sub-bands of Fe atoms in the catalyst alloys could be filled up in proper order by electrons of interstitial carbon atoms. During diamond formation, the unpaired 3d-shell electrons of an iron atom in the Fe-based alloy absorb and interact with 2Pz electrons of the carbon atoms. There exist a Fe–C bonding and an electron charge transfer stage. The 2Pz electrons of the carbon atoms could be dragged into the metal atoms in the catalyst alloy and would make a transition of triangular (sp2π) hybridization of valence electrons to tetrahedral (sp3) hybridization of valence electrons (a transition of sp2π bonds of graphite to sp3 bonds of diamond), resulting in a transition of graphite structure to diamond. Although the conclusion of this study is strictly applicable only to Fe-based alloy catalysts, it could be considered more general because of the chemical similarities between the transition elements used as solvent catalysts for diamond synthesis.
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Received: 2 March 2001 / Accepted: 20 August 2001 / Published online: 2 October 2001
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Yin, LW., Li, MS., Hao, ZY. et al. A new study on the catalytic mechanism of Fe-based alloys in diamond formation by Mössbauer spectroscopy. Appl Phys A 73, 535–538 (2001). https://doi.org/10.1007/s003390101008
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DOI: https://doi.org/10.1007/s003390101008