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  • 1
    Electronic Resource
    Electronic Resource
    Local structures of isovalent and heterovalent dilute impurities in Si crystal probed by fluorescence x-ray absorption fine structure (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4810-4815 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local structures of dilute isovalent and heterovalent impurity atoms in Si crystal (Si:X, X=Ga, Ge, As) have been studied by fluorescence x-ray absorption fine structure. The distortion of local lattice around the impurity atoms was evaluated from the Si–X bond length determined by extended x-ray absorption fine structure. The results demonstrate that the local lattice deformation is strongly dependent on the electronic configuration of impurity atoms, i.e., we find an anomalous expansion (0.09±0.01 Å) along the [111] direction for donor (As) atoms but much smaller magnitude (0.03±0.01 Å) for isovalent (Ge) atoms and acceptor (Ga) atoms. The results suggest that the local lattice distortions are strongly affected by the Coulomb interactions between the localized charge, which piles up to screen the ion core and the bond charge, and the ion-core repulsion. Absence of anomaly in case of negatively charged Ga atoms suggests that the former mechanism is a dominant factor for anomalous lattice expansion. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366340
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  • 2
    Electronic Resource
    Electronic Resource
    Annealed crystallization of ultrafine amorphous NiB alloy studied by XAFS (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 566-568 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: XAFS has been used to investigate the local structure evolutions of ultrafine amorphous NiB alloy during the annealed crystal-lization process. A nanocrystalline Ni phase with the local structure of crystalline Ni-like and a crystalline Ni3B, have been produced for ultrafine amorphous NiB alloy under the annealed temperature of 573 K. The results rule out Rojo et al.'s devitrification mechanism of Ni80B20 amorphous alloy in which they considered that an amorphous pure Ni phase is formed in the first exothermic process. However, our results are almost identical with Riveiro et al.'s conclusion in which the intermediate state is interpreted as two metastable crystalline phases of Ni3B and Ni-rich NiB alloy. With the annealed temperature going onto 773 K, the ultrafine NiB sample is further decomposed and crystallized into crystalline Ni with long-range order.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049500018070
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  • 3
    Electronic Resource
    Electronic Resource
    U7C beamline and XAFS station of National Synchrotron Radiation Laboratory (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 348-350 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The XAFS station on beamline U7C of National Synchrotron Radiation Laboratory (NSRL) was completely constructed in December 1998. The source for XAFS station is from a 3-pole superconducting wiggler with magnetic field of 6 T inserted in the straight section of the storage ring. Using a Si(111) double crystal monochromator with a fixed slit, the X-ray intensity at the sample position is about 3 × 109 photons/second at the energy of 8980 eV of Cu K-edge. The Keithley 6517 electrometers are used to record the electron charges that are produced in the ionization chambers. A high ratio of signal to noise has been obtained for the XAFS spectra of Cu, Ni and Fe foils. Furthermore, the XAFS spectrum of Cu foil in NSRL is in good agreement with that obtained in BSRF and KEK.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049500018045
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  • 4
    Electronic Resource
    Electronic Resource
    Local structures of mechanically alloyed Fe100−xCux solid solutions studied by X-ray absorption fine structure (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 770-772 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The local structures of the immiscible Fe100-xCux alloys (x= 0, 10, 20, 40, 60, 80 and 100) produced by mechanical alloying have been investigated by XAFS. For the Fe100-xCux (x ≥ 40) solid solutions, the local structures around Fe atoms change from bcc structure to fcc one and the Cu atoms maintain the original coordination geometry after milling for 160 hours. On the contrary, the local structures around Cu atoms in both of Fe80Cu20 and Fe90Cu10 alloys appear a transition from fcc to bcc structure. We found that the Debye-waller factor σ of fcc Fe-Cu phase is larger than that of bcc Fe-Cu phase, and the σ (0.099 Å) around Fe atoms is larger than that (0.089 Å) of Cu in the Fe100-xCux (x ≥ 40) solid solutions. This suggests that the mechanically alloyed Fe100-xCux supersaturated solid solution is not a homogeneous alloy, and consists of Fe-rich and Cu-rich regions for various compositions. A possible mechanism for bcc-to-fcc and fcc-to-bcc changes in Fe100-xCux solid solutions is discussed in relation to the interdiffusion and transition induced by the ball milling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049500018318
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  • 5
    Electronic Resource
    Electronic Resource
    Local structures of nanocrystalline GaN studied by XAFS (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 830-832 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray absorption fine structure (XAFS) was used to investigate the local structures around Ga atoms in the hexagonal nanocrystalline and crystalline GaN under 78 and 300 K. For the first nearest neighbor coordination shell of Ga-N, the average bond length R (0.194 nm), coordination number N (4.0), thermal disorder σT (0.0052 nm) and static disorder σS (0.0007 nm) are nearly independent of the measured temperature and crystalline state. This indicates that the Ga-N covalent bond is much stronger, and the 4 nitrogen atoms in first nearest neighbor around Ga atoms keep the tetrahedral structure (Td). For the second nearest neighbor coordination shell of Ga-Ga, their bond lengths are about 0.318 nm. However, the σS (0.0057 nm) of nanocrystalline GaN is 0.0047 nm larger than that of crystalline GaN (0.001nm), and the σT of nanocrystalline is 0.0053 nm and 0.0085 nm at the temperature of 78 and 300 K, respectively. The result indicates that the difference of local structure around Ga atoms between nanocrystalline and crystalline GaN occurs mainly at the Ga-Ga second nearest-neighbor coordination shell. The reason is explained as the local lattice distortion and unsaturated surface atoms existing in nanocrystalline GaN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049501000103
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  • 6
    Electronic Resource
    Electronic Resource
    Local structure evolution of FexNi77–xCu1Nb2P14B6 soft magnetic materials by mechanical alloying (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 889-891 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Mechanically alloyed FexNi77-xCu1Nb2P14B6 soft magnetic materials have been prepared with different atomic compositions. The alloy structures are investigated by X-ray absorption fine structure (XAFS). The results show that mechanical alloying (MA) can drive the FexNi77-xCu1Nb2P14B6 powder mixture to produce amorphous alloy while the atomic concentration of Fe element is about and over 40%. On the contrary, the MA FexNi77-xCu1Nb2P14B6 is a solid solution with a fcc-like structure in the region of lower Fe atomic concentration (〈22%), preserving a medium-range order around Ni and Fe atoms. Moreover, we have found that the local structure geometry of Fe atom is similar to that of Ni atom for all the MA FexNi77-xCu1Nb2P14B6 samples. It indicates that the local structures of Fe and Ni atoms in a FexNi77-xCu1Nb2P14B6 sample only depend on the x value of element Ni after ball milling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S090904950001671X
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