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  • 11
    Electronic Resource
    Electronic Resource
    Laser surface-melting of metals studied by PAC (1990)
    Springer
    Hyperfine interactions 61 (1990), S. 1339-1342 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High purity Pt, Ni, Cu, Fe and Al metal foils were electroplated with carrier-free111In probe atoms and melted at 293 K using 32 ns ruby laser pulses with energy densities in the range 1–10 J cm−2. Three distinct lattice locations of the probe atoms were detected in the melted surface layers using perturbed γ-γ angular correlation spectroscopy: (i) defect-free substitutional sites, (ii) non-unique sites with broad distributions of quadrupole interactions, and (iii) a probemonovacancy complex (for Pt only). The defect-free fraction was found to approach 100% when Pt is irradiated at 9 J cm−2. The fraction of probes on defect-free sites was found to increase with the energy density of the pulse and with the solubility of In in the metals. The data are consistent with the idea that laser surface-melting produces high concentrations of vacancies and lattice sinks, although no thermal trapping of point defects was detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02407620
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  • 12
    Electronic Resource
    Electronic Resource
    Hydrogen binding in vacancy clusters in platinum (1993)
    Springer
    Hyperfine interactions 79 (1993), S. 749-753 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The binding of hydrogen in different vacancy complexes in platinum metal was investigated with atomic-scale sensitivity using perturbed angular correlations of gamma rays (PAC). Hydrogen was introduced by cathodic charging. Detrapping was monitored microscopically during desorption at 294 K by changes in site fractions of hydrogen-decorated and undecorated complexes. Analysis of desorption includes effects of retrapping of hydrogen at other sites. Assuming a trap concentration of 10−3, binding enthalpies of 0.23(2), 0.28(1), 0.24(1) and 〉0.20 eV are obtained for hydrogen atoms in 1V to 4V complexes, respectively. The small differences between the binding enthalpies demonstrate that hydrogen binding is insensitive to the detailed geometrical structure of small vacancy complexes. However, the magnitudes found here are a factor of two smaller than in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567603
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  • 13
    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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  • 14
    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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  • 15
    Electronic Resource
    Electronic Resource
    Application of PAC to study equilibrium point defects in intermetallic compounds (1993)
    Springer
    Hyperfine interactions 80 (1993), S. 1257-1261 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new method has been developed to measure properties of equilibrium, or thermal, defects in intermetallics using the technique of perturbed angular correlations of gamma rays (PAC). After quenching, thermal defects are detected microscopically by distinctive nuclear hyperfine interaction signals produced when they localize next to probe atoms present in high dilution. Using a Schottky defect model and applying the law of mass action to defect equilibria, a linear Arrhenius temperature dependence is predicted for a “normalized” monovacancy site fraction. We have observed such linear dependences in PAC experiments on NiAl, CoAl and TiAl using the111In probe. Features of the method are summarized, of which the most important are the abilities to discriminate between different defects and to determine absolute vacancy concentrations, formation enthalpies and entropies. Extremely large formation entropies have been obtained for NiAl, CoAl and TiAl, suggesting vacancy concentrations of ∼ 15% at the melting temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567488
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  • 16
    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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  • 17
    Electronic Resource
    Electronic Resource
    Atomic diffusion in strain fields near solutes (1993)
    Springer
    Hyperfine interactions 79 (1993), S. 755-760 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Annihilation reactions between mobile self-interstitial defects and complexes of vacancies with111In probe solutes in Au were studied. Measurements were made using the technique of perturbed angular correlations of gamma rays (PAC). Au samples were doped with complexes and plastically deformed at a low temperature to generate fluxes of self-interstitials. Changes in the concentrations of monovacancy (1V) to tetravacancy (4V) complexes induced by annihilation reactions were measured. These are now analysed using a system of coupled first-order equations in order to obtain interstitial annihilation cross sections of the complexes and the fractional amounts of different interstitial clusters in the flux. Relative cross sections obtained for Au are 1.0(1), 3.3(3), 1.2(2) and 7.5(2.5), respectively, for 1V to 4V complexes. The large increase in the cross sections with vacancy number is attributed to a progressive relaxation of the dilatational strain surrounding the oversized In solute as more vacancies are trapped. Also obtained from the analysis are values 0.34(5), 0.66(7), 0.0(1) and 0.0(2), respectively, for the fractions of mobile 1I to 4I clusters in deformed Au, indicating that di-interstitials are produced more readily than mono-interstitials during plastic deformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567604
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  • 18
    Electronic Resource
    Electronic Resource
    Trivacancy recovery and formation of a cubic symmetry defect trap on111In impurities in Ni (1983)
    Springer
    Hyperfine interactions 15 (1983), S. 391-394 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using perturbed angular correlations we studied the formation of a cubic symmetry defect trap in Ni near 350 K following plastic deformation at 295 K. The trap has been identified structurally as a trivacancy trap. The evolution of the defect-free and cubic trap site populations in the course of isochronal and isothermal annealing experiments leads to the conclusion that the cubic trap forms by simple trapping, and that the capture radius of the cubic trap for additional defects is very small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02159775
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  • 19
    Electronic Resource
    Electronic Resource
    Anomalous temperature dependence of the quadrupole coupling frequency of a lattice defect trapped to111In in Pt (1983)
    Springer
    Hyperfine interactions 15 (1983), S. 395-399 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The quadrupole coupling frequency of an111In-defect bound state in Pt with ω0(295 K) = 200 Mrad/s was measured over the range 4 – 300 K using perturbed angular correlations. The temperature dependence exhibited positive curvature, unlike the T3/2 dependence observed in noncubic metals, and was fitted using a model which assumed that the temperature dependence was caused by vibrations of a resonant mode in the probe-defect complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02159776
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  • 20
    Electronic Resource
    Electronic Resource
    Nuclear spin relaxation of161Dy in Gd above the Curie temperature observed with the Mössbauer effect (1983)
    Springer
    Hyperfine interactions 16 (1983), S. 617-620 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using a source of181Tb, we have observed a substantial linewidth anomaly in the161Dy Mössbauer Effect just above the Curie temperature of Gd. Preliminary analysis of the anomaly is consistent with behavior expected for critical spin dynamics. Uncertainty in the Curie temperature prevents conclusive analysis of the linewidth divergence in terms of the dynamical exponent, z.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02147326
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