Experimental Measurement of Valence Electron Concentration of Icosahedral AlPdMn Quasicrystal

来源 :Wuhan University Journal of Natural Sciences | 被引量 : 0次 | 上传用户:spls108
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The valence charge density distribution for the icosahedral AlPdMn (i-AlPdMn) quasicrystal was obtained with the structure factors of the nine strongest symmetry inequivalent reflections, which were refined by using the quantitative convergent beam electron diffraction (QCBED) technique. It shows that the bonding charge is localized. The enhanced charge density in the middle of the aluminum-transition-metal (Al-TM) bond shown in the valence charge density distribution is the characteristic of covalent bonding. Assuming that the shape of an atom is a sphere with covalent radius, the number of electrons that each atom gains or loses in 55 different pseudo-Mackay clusters (PMCs) was cal- culated based on the obtained valence charge density distribution. It indicates that almost all the atoms lose electrons except a few Pd atoms that are in some particular shells. It also shows that the atoms of an identified element could have different valences because of chemically and/or structurally different local environments in which the atoms situ- ate. Regardless of the topology and chemical occupancy, the number of valence electrons per atom in a cluster is close to 1.69. This strongly suggests that the pseudo-Mackay clusters are stabilized at a certain elec- tron concentration. The valence charge density distribution for the icosahedral AlPdMn (i-AlPdMn) quasicrystal was obtained with the structure factors of the nine strongest symmetry inequivalent reflections, which were refined by using the quantitative convergent beam electron diffraction (QCBED) technique. The enhanced charge density in the middle of the aluminum-transition-metal (Al-TM) bond shown in the valence charge density distribution is the characteristic of covalent bonding. Assuming that the shape of an atom is a sphere with covalent radius, the number of electrons that each atom gains or loses in 55 different pseudo-Mackay clusters (PMCs) was cal-culated based on the obtained valence charge density distribution. It indicates that almost all the atoms lose electrons except a few Pd atoms that are also some special shells. It also shows that the atoms of an identified element could have different valences because of chemically and / or structurally d ifferent local environments in which the atoms situ- ate. Regardless of the topology and chemical occupancy, the number of valence electrons per atom in a cluster is close to 1.69. This suggests means that the pseudo-Mackay clusters are stabilized at a certain elec- tron concentration
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