The atomic structure of the perfect AlPdMn icosahedral phase has been studied on a single crystal specimen by quantitative convergent beam electron diffraction (QCBED) technique in combination with describing the shap...The atomic structure of the perfect AlPdMn icosahedral phase has been studied on a single crystal specimen by quantitative convergent beam electron diffraction (QCBED) technique in combination with describing the shape of atomic surface by symmetry\|adapted series of surface harmonics. The spherical model was used as the starting model for the refinement. By fitting the calculated electron diffraction intensities to the experimental line scan profile, the coefficients in the surface harmonics expansion of the boundaries of atomic surface are refined. The refined parameters show that the fluctuations of the external boundary of atomic surface for Pd at n 0 can be as large as 0.2 nm. The boundaries of atomic surfaces for Mn show little fluctuation. In the present model, the number of unphysically short interatomic distances is significantly reduced in comparison with the spherical model.展开更多
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 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.展开更多
基金Supported by the National Natural Science Foundation of China (59871034)
文摘The atomic structure of the perfect AlPdMn icosahedral phase has been studied on a single crystal specimen by quantitative convergent beam electron diffraction (QCBED) technique in combination with describing the shape of atomic surface by symmetry\|adapted series of surface harmonics. The spherical model was used as the starting model for the refinement. By fitting the calculated electron diffraction intensities to the experimental line scan profile, the coefficients in the surface harmonics expansion of the boundaries of atomic surface are refined. The refined parameters show that the fluctuations of the external boundary of atomic surface for Pd at n 0 can be as large as 0.2 nm. The boundaries of atomic surfaces for Mn show little fluctuation. In the present model, the number of unphysically short interatomic distances is significantly reduced in comparison with the spherical model.
基金Supported by the National Natural Science Foundation of China (50671073)
文摘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.
