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  • 2000-2004  (1)
  • 1995-1999  (2)
  • 1990-1994  (19)
  • 1980-1984  (4)
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  • 2000-2004  (1)
  • 1995-1999  (2)
  • 1990-1994  (19)
  • 1980-1984  (4)
  • 1985-1989  (2)
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  • 11
    Electronic Resource
    Electronic Resource
    Point defects in NiAl near the equiatomic composition (1990)
    Springer
    Hyperfine interactions 60 (1990), S. 655-658 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Perturbed γ-γ angular correlation spectroscopy was applied to study the structure and properties of point defects near111In probes in quenched and annealed NiAl samples with five compositions in the range cNi=48–52%. Quadrupole interaction signals are analysed in terms of near-neighbor Ni-vacancy and nextnear-neighbor Ni antisite atom defects. Large mono- and divacancy concentrations were observed in all samples after quenching. For cNi〈50%, the vacancy defects could not be annealed out (structural defects). For CNi〉50%, large quenched-in vacancy concentrations annealed out near 500°C. For cNi=50%, most vacancies annealed out near 500°C, but about 35% of the111In probes retained a trapped monovacancy. This is attributed to a very low value of the formation enthalpy of a vacancy next to the In probe, estimated to be 0.16(2) eV. A lesser annelaing stage detected at 300°C is tentatively attributed to diffusion of Al-vacancies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399838
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  • 12
    Electronic Resource
    Electronic Resource
    Production and migration of interstitials in deformed metals (1990)
    Springer
    Hyperfine interactions 60 (1990), S. 667-670 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An investigation was made of defect production during plastic deformation. Prior to cold-rolling, samples of Au were damaged and preannealed at temperatures in order to maximize site fractions of five different In-vacancy defect complexes, such as In-1V and In-2V. Evolutions of site fractions were monitored by perturbed γ-γ angular correlation spectroscopy after additional strains at 77 K. Observed transformations between sites are consistent with defect-antidefect annihilation reactions between the small complexes and mobile interstitials, and indicate a large production of interstitials during deformation. An extended defect complex attributed to a planar faulted loop became glissile under small strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399841
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  • 13
    Electronic Resource
    Electronic Resource
    Cage motion of a probe atom in a vacancy complex in Pt (1990)
    Springer
    Hyperfine interactions 60 (1990), S. 651-653 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The perturbation function of a Cd probe atom bound in a hydrogen-decorated vacancy complex in Pt is found to exhibit dynamical relaxation at 294 K, as measured by the technique of perturbed γ-γ angular correlations. Based on other characteristics of the complex, a model is proposed for the structure of the complex. In the undecorated state, it consists of a probe atom at the center of a tetrahedron of vacancies in the fcc structure. In the decorated state at low temperature, the probe atom returns to one of the four vacant lattice sites. The relaxation at room temperature is attributed to motion of the probe atom in a cage formed by the four vacant sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399837
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  • 14
    Electronic Resource
    Electronic Resource
    Stacking fault defects in hep cobalt studied by PAC (1990)
    Springer
    Hyperfine interactions 60 (1990), S. 659-662 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study was made of lattice defects in hep Co metal using the technique of perturbed γ-γ angular correlations. Lattice sites of111Cd impurities were characterized by their nuclear magnetic dipole and electric quadrupole interaction frequencies, respectively ωL and ωO. The signal for defect-free substitutional Cd impurities was found to have collinear interactions at 77K, with ωL=438 Mrad/s and ωO=7 Mrad/s. Analysis of measurements after heavy deformation at 100 K and after annealings up to 700 K gave little evidence of thermal trapping of point defects. However, in all spectral measured after deformation, a highly stable defect site with ωL=418 and ωO Mrad/s, and showing collinear interactions, was also observed. It is attributed to a111Cd probe in a stacking fault (SF). Assuming a random distribution of proble atoms and SF's, a SF density of 20% was estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399839
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  • 15
    Electronic Resource
    Electronic Resource
    Electrolytic loading of hydrogen in metals studied by PAC (1990)
    Springer
    Hyperfine interactions 60 (1990), S. 663-666 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In previous work, we introduced hydrogen (H) into Ni and Pt metals at room temperature by electrolysis. To study H-vacancy interactions on an atomic scale, trapping of diffusing H atoms at impurity-vancancy complexes was detected using perturbed γ-γ angular correlations. Two new results are reported here: (1) Transformation rules are clarified between undecorated and H-decorated complexes which are detected after annealing Pt at 323 K. In addition, non-cubic In sites were observed to form by chargingannealed, Pt, which are attiributed either to H atoms at random in the lattice or to precursor nuclei of a Pt hydride. (2) NiH is observed to form under cathodic charging of Ni at high current densities, and detected by growth of a nonmagnetic, cubic metastable phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399840
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  • 16
    Electronic Resource
    Electronic Resource
    Perturbed γ−γ angular correlations: A spectroscopy for point defects in metals and alloys (1990)
    Springer
    Hyperfine interactions 62 (1990), S. 1-34 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Atomic defects which migrate and trap at impurity probe atoms can be labelled by the changes they induce in the hyperfine interactions of the probe nuclei. Many studies have been made using perturbed γ−γ angular correlations (PAC) and the111In probe because of the excellent resolution of different sites. Identification of the bound states is the key problem in applying hyperfine interactions methods to point defects studies. In this study three structure-sensitive methods are applied to help identify the atomic structures of various multivacancy complexes in Pt and Au: (1) Quadrupole interaction parameters are compared with results of point-charge calculations of electric-field gradients for 20 structures containing 1–4 vacancies in the fcc lattice. (2) Hyperfine interactions induced by decorating vacancy complexes with hydrogen atoms are measured and interpreted with the assistance of point-charge calculations. (3) Transformations between complexes observed by annihilation of vacancies by mobile self-interstitials are used to test the consistency of the identifications. Using these methods in conjunction with analysis of the trapping behavior which occurs during annealing of damaged samples, structural models are presented for divacancy (2V), 3V and 4V complexes in Pt, and 3V and 4V complexes in Au. The activation temperatures of the 3V defect in Au and Pt are determined to be 162 K and 390 K, respectively, and activation temperatures of defects in Ni, Cu, Pt and Au are compared. For Pt, trapping of H at 1V and 2V complexes is observed to lead to small changes in the quadrupole interactions, consistent with well shielded protonic charges. However, trapping at 3V and 4V complexes leads to very large changes which we attribute to atomic restructuring to the defect complexes. Finally, the application of the same methodology to interpret recent experiments on NiAl, an ordered alloy, is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02407659
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  • 17
    Electronic Resource
    Electronic Resource
    Grain boundary sites in fcc metals studied by PAC (1993)
    Springer
    Hyperfine interactions 79 (1993), S. 761-764 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Perturbed angular correlation of gamma rays (PAC) is applied to study the atomic structure of grain boundaries (gb) in fcc metals using nuclear quadrupole interactions.111In probes were diffused in samples of Au, Cu, Ni and Pt which had first been annealed to form high-angle gbs. Diffusions were carried out at such low temperatures that only gb diffusion should occur (Harrison's type-C kinetic regime), and measurements were made after removing any residual surface activity. For three Pt samples, a unique signal attributed to a gb site was detected with a site fraction of about 50%, coupling frequency ω1=80.0(2) Mrad/s and electric-field-gradient asymmetry parameter η=0. A Pt sample of 99.9995% purity exhibited much less inhomogeneous signal broadening than 99.998% pure samples, indicating the level of purity necessary to observe the gb sites via quadrupole interactions. The broadening is attributed to gb segregation. For Au, Cu and Ni, only ill-defined, non-unique signals were detected, apparently because of gb segregation. The small broadening in the high-purity Pt sample indicates a high degree of uniformity in the crystal structure of the high-angle gb sites. The large site fraction of the 80 Mrad/s signal demonstrates the dominance of a single site for Cd probes in high-angle gbs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567605
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  • 18
    Electronic Resource
    Electronic Resource
    Formation of Ni3Fe by mechanical alloying (1994)
    Springer
    Hyperfine interactions 92 (1994), S. 955-958 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ni and Fe powders in a 75∶25 atomic proportion were mechanically alloyed using a high-energy ball mill.57Fe Mössbauer measurements were made to determine the reaction mechanism for alloy formation by means of analysis of the evolution of the Fe hyperfine fields during milling. After a latent period of 2 hours, the spectral area of an Fe-like component decreased monotonically with milling time, disappearing after 8 hours. It was replaced by a well-resolved Zeeman pattern with hyperfine fieldH=29.1 T and outer lines of width 0.75 mm/s which is attributed to Fe in disordered Ni3Fe. The evolution of hyperfine fields rules out alloy formation by dissolution of Ni in the Fe matrix or of Fe in the Ni matrix, so that formation must occur by reaction of Ni and Fe at the interfaces between their grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02065718
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  • 19
    Electronic Resource
    Electronic Resource
    Indium metal nanoclusters studied by PAC (1993)
    Springer
    Hyperfine interactions 80 (1993), S. 1117-1120 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The technique of perturbed angular correlations of gamma rays (PAC) is applied for the first time to study the structure of small metal clusters. Metal clusters containing111In probe atoms with 50 nm radii were synthesized by dissolving InCl3 containing111In in hexane using a surfactant, thereby creating an inverse micellar solution. The salt was then reduced to metal form by addition of NaBH4. 100% conversion efficiency of In salt to metal clusters was achieved. PAC measurements at 293 K on the111Cd daughter nuclide exhibited a nuclear quadrupole interaction with coupling frequency ω0=16.0(5) Mrad/s and a small asymmetry parameter, η=0.20(4). The frequency is as observed for bulk In crystals, but a non-zero value of η has not been previously reported. Lack of inhomogeneous signal broadening and the faceted shape of some nanoclusters suggest high crystal perfection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567473
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  • 20
    Electronic Resource
    Electronic Resource
    Equilibrium point defects in TiAl studied by PAC (1993)
    Springer
    Hyperfine interactions 79 (1993), S. 745-748 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Site fractions of dilute111In/111Cd probe atoms in different lattice locations in quenched, equi-atomic TiAl are measured using perturbed angular correlations of gamma rays (PAC). The vacancy-free substitutional site fraction, observed via its nuclear quadrupole interaction, is observed to decrease with increasing quenching temperature, reflecting an increase in the thermal defect concentration. Assuming that the thermal defect is the Schottky defect, the law of mass action, and a binding energy of 0.2 eV between vacancies and the In probe, the experimental temperature dependence is analysed to yield a formation enthalpy of 4.7(4) eV and entropy of 25(4)k B for the Schottky defect. The vacancy concentration on one sublattice is given in terms of these parameters by the expression [v]=exp(S F/2k B) exp(−E F/2k B T), and is found, for example, to have the value 1.4% at 1350°C, a large value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567602
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