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  • 11
    Electronic Resource
    Electronic Resource
    Phases and phase stabilities of Fe3X alloys (X=Al, As, Ge, In, Sb, Si, Sn, Zn) prepared by mechanical alloying (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5961-5966 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanical alloying with a Spex 8000 mixer/mill was used to prepare several alloys of the Fe3X composition, where the solutes X were from groups IIB, IIIB, IVB, and VB of the periodic table. Using x-ray diffractometry and Mössbauer spectrometry, we determined the steady-state phases after milling for long times. The tendencies of the alloys to form the bcc phase after milling are predicted well with the modified usage of a Darken–Gurry plot of electronegativity versus metallic radius. Thermal stabilities of some of these phases were studied. In the cases of Fe3Ge and Fe3Sn, there was the formation of transient D03 and B2 order during annealing, although this ordered structure was replaced by equilibrium phases upon further annealing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358375
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  • 12
    Electronic Resource
    Electronic Resource
    Microstructural dependence of vacancy diffusion in ordered alloys (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1467-1472 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the vacancy diffusional correlation factor on microstructure was investigated by Monte Carlo simulations (MCS). The MCS used activated state rate theory to model the vacancy diffusion. We varied the temperature, size of ordered domains, and the state of order within the domains. Correlations in the vacancy movement were found to vary widely, and numerical values are presented. Two different results were obtained, one for ordering in a homogeneous alloy and another for ordering in an alloy having domains. However, given the existence of domains, the vacancy correlation factor was observed to be independent of domain size. Oscillations in the correlation function were observed, and were attributed to pair trapping of the vacancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356381
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  • 13
    Electronic Resource
    Electronic Resource
    Structure and magnetic properties of sputtered thin films of Fe0.79Ge0.21 (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5117-5123 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Films of Fe0.79Ge0.21 with thicknesses of 300 nm were synthesized by ion beam sputtering, and were annealed at temperatures from 200 to 550 °C. The materials were characterized by x-ray diffractometry, Mössbauer spectrometry, vibrating sample magnetometry, ferromagnetic resonance spectrometry, and electrical resistivity measurements. The as-prepared materials comprised chemically disordered bcc crystallites of sizes less than 20 nm, and were found to have a distribution of internal strains. Upon annealing at temperatures of 250 °C and below, there occurred strain relaxation, some evolution of short range chemical order, and an improvement in soft magnetic properties. The coercive field was a minimum for the sample annealed at 250 °C. Crystallite growth occurred at higher annealing temperatures, accompanied by a transition in several measured parameters from those of ultrafine grained materials to those typical of polycrystalline materials. This trend can be explained with the random anisotropy model. Mössbauer and magnetization measurements indicated that the Ge atoms behave as magnetic holes. The 57Fe hyperfine magnetic field distribution, and its change during chemical ordering, can be calculated approximately with a model of magnetic response. The large local isomer shifts at 57Fe atoms near Ge atoms suggest that a local depletion of 4s conduction electron density should be incorporated into the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354298
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  • 14
    Electronic Resource
    Electronic Resource
    Percolation in alloys with thermally activated diffusion (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4752-4755 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For diffusion in a real alloy, some concepts of formal percolation theory may need to be reconsidered because the "immobile'' atoms are not truly immobile. Our Monte Carlo simulations of vacancy diffusion on bcc lattices show the existence of a relationship between the activation barrier heights for the vacancy-atom exchanges and the effective percolation threshold concentration. In the language of formal percolation theory, we have modeled this problem by varying the immobile species' barrier height from infinity to some finite value and calculating the resulting percolation threshold. When both species of atoms have a finite mobility, however, our results can be interpreted in terms of probabilities for vacancies to escape local clusters in a fixed amount of time. We find that the dynamical behavior undergoes a marked change above and below the formal percolation threshold, but the strength of the percolating cluster is much less important than in formal percolation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343785
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  • 15
    Electronic Resource
    Electronic Resource
    Magnetomechanical effects in textured polycrystalline Tb76Dy24 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5795-5797 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Uniaxial stress-strain measurements were performed on polycrystalline Tb76Dy24 alloys which exhibit "giant magnetostriction" at cryogenic temperatures. The Young's moduli were reduced by up to a factor of five at 77 K, in comparison to their values at 300 K. We attribute this reduction to a mechanical compliance from domain rotation. Large mechanical hysteresis is also found in nominally elastic stress-strain curves measured below the Curie temperature. Hysteretic curves from 0 to 25 MPa demonstrate up to 19% dissipation of the applied mechanical energy. The anisotropy of thermal expansion was also measured and used as a parameter for the degree of crystallographic texture. This anisotropy was correlated to bulk magnetostriction and to mechanical hysteresis. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372525
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  • 16
    Electronic Resource
    Electronic Resource
    A small angle neutron scattering and Mössbauer spectrometry study of magnetic structures in nanocrystalline Ni3Fe (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 7097-7104 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are reported from small angle neutron scattering and Mössbauer spectrometry measurements on nanocrystalline Ni3Fe. The nanocrystalline materials were prepared by mechanical attrition and studied in the as-milled state, after annealing at 265 °C to relieve internal stress, and after annealing 600 °C to prepare a control sample comprising large crystals. The small angle neutron scattering (SANS) measurements were performed for a range of applied magnetic fields. Small differences were found in how the different samples reached magnetic saturation. From the SANS data obtained at magnetic saturation, we found little difference in the nuclear scattering of the as-milled material and the material annealed at 265 °C. Reductions in nuclear scattering and magnetic scattering were observed for the control sample, and this was interpreted as grain growth. The material annealed at 265 °C also showed a reduction in magnetic SANS compared to the as-milled material. This was interpreted as an increase in magnetic moments of atoms at the grain boundaries after a low temperature annealing. Both Mössbauer spectroscopy and small angle neutron scattering showed an increase in the grain boundary magnetic moments after the 265 °C annealing (0.2 and 0.4μB/atom, respectively), even though there was little change in the grain boundary atomic density. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370517
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  • 17
    Electronic Resource
    Electronic Resource
    Electron energy-loss spectrometry on lithiated graphite (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 238-240 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron energy-loss spectrometry was used to investigate the electronic states of metallic Li and LiC6, which is the Li-intercalated graphite used in Li-ion batteries. The Li K edges of metallic Li and LiC6 were nearly identical, and the C K edges were only weakly affected by the presence of Li. These results suggest only a small charge transfer from Li to C in LiC6, contrary to prior results from surface spectra obtained by x-ray photoelectron spectroscopy. Effects of radiation damage and sample oxidation in the transmission electron microscopy are also reported. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126936
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  • 18
    Electronic Resource
    Electronic Resource
    Hydrogen desorption and adsorption measurements on graphite nanofibers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3378-3380 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Graphite nanofibers were synthesized and their hydrogen desorption and adsorption properties are reported for 77 and 300 K. Catalysts were made by several different methods including chemical routes, mechanical alloying, and gas condensation. The nanofibers were grown by passing ethylene and H2 gases over the catalysts at 600 °C. Hydrogen desorption and adsorption were measured using a volumetric analysis Sieverts' apparatus, and the graphite nanofibers were characterized by transmission electron microscopy and Brunauer–Emmett–Teller surface area analysis. The absolute level of hydrogen desorption measured from these materials was typically less than the 0.01 H/C atom, comparable to other forms of carbon. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122755
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  • 19
    Electronic Resource
    Electronic Resource
    Hydrogen adsorption and phase transitions in fullerite (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2171-2173 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogen desorption and adsorption properties of the fullerene materials C60, C70, and fullerite (a mixture of C60 and C70) were measured volumetrically using a Sievert's apparatus. Over several cycles of isotherm measurements at 77 K, the hydrogen storage capacities of one of the fullerite samples increased from an initial value of 0.4 wt % for the first cycle to a capacity of 4.4 wt % for the fourth cycle. Correspondingly, the surface area of this sample increased from 0.9 to 11 m2/g, and there were changes in its x-ray powder diffraction pattern. In comparison, two other fullerite samples, prepared by a different procedure showed no such behavior. Pure C60 and pure C70 were also cycled and exhibited small and constant capacities of 0.7 and 0.33 wt %, respectively, as a function of number of cycles. The enhanced storage capacity of fullerite material is tentatively attributed to the presence of C60 oxide. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1312857
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  • 20
    Electronic Resource
    Electronic Resource
    Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2307-2309 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogen adsorption on crystalline ropes of carbon single-walled nanotubes (SWNT) was found to exceed 8 wt. %, which is the highest capacity of any carbon material. Hydrogen is first adsorbed on the outer surfaces of the crystalline ropes. At pressures higher than about 40 bar at 80 K, however, a phase transition occurs where there is a separation of the individual SWNTs, and hydrogen is physisorbed on their exposed surfaces. The pressure of this phase transition provides a tube-tube cohesive energy for much of the material of 5 meV/C atom. This small cohesive energy is affected strongly by the quality of crystalline order in the ropes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123833
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