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Articles 1 - 9 of 9

Full-Text Articles in Physics

Twinned One-Dimensional Quasicrystals In Bridgman-Grown Al-Si-Cu-Co Alloys, L. X. He, Thomas A. Lograsso, Alan I. Goldman Jul 1992

Twinned One-Dimensional Quasicrystals In Bridgman-Grown Al-Si-Cu-Co Alloys, L. X. He, Thomas A. Lograsso, Alan I. Goldman

Ames Laboratory Publications

Single grains of Al60Si2Cu18Co20 with a decaprismatic morphology were grown by the Bridgman method and studied by transmission electron microscopy and x-ray diffraction. Although the diffraction patterns of these grains superficially resemble that of a decagonal quasicrystal, a closer inspection reveals that they are composed of tenfold twins of a one-dimensional quasicrystal along with small domains of three crystalline approximant phases.


Relaxation And Fluctuations In Glassy Fast-Ion Conductors: Wide-Frequency-Range Nmr And Conductivity Measurements, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin, Hitendra K. Patel Jul 1992

Relaxation And Fluctuations In Glassy Fast-Ion Conductors: Wide-Frequency-Range Nmr And Conductivity Measurements, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin, Hitendra K. Patel

Materials Science and Engineering Publications

Li7 nuclear spin-lattice relaxation rates (R1) versus the temperature at several resonance frequencies (4 to 40 MHz) are reported together with the conductivity measurements, σ(ω), in the range 1 Hz to 3.76 MHz on 0.56Li2S+0.44Si2S, a glassy fast-ionic conductor. Both R1 and σ(ω) are fitted consistently over the whole temperature and frequency range by using a stretched-exponential, i.e., exp(-t/τ*c)β for the corresponding correlation functions (CF). Formulas that relate R1(ω) and σ(ω) and that give the asymptotic behavior as functions of T and ω of both quantities are ...


Fast Ionic Conduction In Na2s+B2s3 Glasses: Compositional Contributions To Nonexponentiality In Conductivity Relaxation In The Extreme Low-Alkali-Metal Limit, Hitendra K. Patel, Steve W. Martin May 1992

Fast Ionic Conduction In Na2s+B2s3 Glasses: Compositional Contributions To Nonexponentiality In Conductivity Relaxation In The Extreme Low-Alkali-Metal Limit, Hitendra K. Patel, Steve W. Martin

Materials Science and Engineering Publications

The conductivity relaxation phenomenon in glassy and crystalline ionic conductors has been known for many years to be a highly nonexponential process. The stretched exponential function exp-(t/τ)β has been used with varying levels of success to describe this relaxation. Whether the nonexponentiality is due to parallel conducting processes acting independently of each other and having a distribution of relaxation times or to serial processes strongly coupling the ionically conducting species and constraining each other’s relaxation, the exact nature of this process is still unknown. If coupling is the active mechanism responsible for the nonexponentiality, then there ...


Pinski Et Al. Reply, F. J. Pinski, B. Ginatempo, Duane D. Johnson, J. B. Staunton, G. M. Stocks, B. L. Gyorffy Mar 1992

Pinski Et Al. Reply, F. J. Pinski, B. Ginatempo, Duane D. Johnson, J. B. Staunton, G. M. Stocks, B. L. Gyorffy

Duane D. Johnson

With our calculations [I], we uncovered the electronic mechanism responsible for inducing atomic short-range order (SRO) in the disordered solid solution of NiPt as it is cooled. Usually, but not always, SRO, whether derived theoretically or measured experimentally, indicates the nature of the long-rangeordered (LRO) state that will stabilize at low temperature. Our calculation of the atomic SRO, while agreeing with experiments [2], neglected the relativistic effects in the electronic structure. Lu, Wei, and Zunger (LWZ) [3,4], on the other hand, have calculated the L lo-ordered alloy formation energy and find that only when relativistic effects are included is ...


Tem Observations Of The Mechanism Of Delamination Of Chromium Films From Silicon Substrates, D. Goyal, Alexander H. King Feb 1992

Tem Observations Of The Mechanism Of Delamination Of Chromium Films From Silicon Substrates, D. Goyal, Alexander H. King

Alexander H. King

We have observed the complete delamination of polycrystalline chromium films from single crystal silicon substrates during deposition due to the formation of high internal stresses. These intrinsic stresses can give rise to interfacial defects which assist in the separation of the film from the substrate. Stresses in the film are balanced by stresses in the substrate, which cause mechanical failure in the substrate near the interface. Extensive arrays of dislocations and cracking of the substrate have been observed. We find that the delamination of the films from the substrate is initiated by the formation of damage in the substrate, rather ...


Structure And Stability Of Al-Cu-Ru Face-Centered Icosahedral Alloys , Jeffrey E. Shield Jan 1992

Structure And Stability Of Al-Cu-Ru Face-Centered Icosahedral Alloys , Jeffrey E. Shield

Retrospective Theses and Dissertations

The phases and microstructures in rapidly solidified Al-Cu-Ru alloys were investigated in this study. A chemically and topologically disordered icosahedral (i) phase grows dendritically from the liquid as the primary solidification product over the entire compositional region studied. The as-solidified i-phase is metastable and transforms to crystalline products at ≈500°C. The i-phase was not found as a product of the exothermic transformation for any composition, indicating that it is not the low temperature stable phase in the Al-Cu-Ru system;A chemically and topologically ordered i-phase was found to be an equilibrium phase at temperatures above ≈670°C and exists ...


Study Of Beamforming Techniques For Ultrasound Imaging In Nondestructive Testing , Sleiman Riad Ghorayeb Jan 1992

Study Of Beamforming Techniques For Ultrasound Imaging In Nondestructive Testing , Sleiman Riad Ghorayeb

Retrospective Theses and Dissertations

Many of the innovations in modern materials testing technology make use of ultrasound. Therefore, the theory and application of ultrasound have become of extreme importance in nondestructive inspection of complete engineered systems. However, despite the fact that most of these ultrasound inspection techniques are based on well-established phenomena, two key problems pertaining to their application still remain unresolved. These problems can be identified as (1) the material being tested is assumed to be isotropic and homogeneous by nature, and (2) the scanning/data collection process, prior to the reconstruction scheme, is very time consuming. As a result, techniques for fast ...


Neutron Diffraction Study Of The Electronic Structure Of High-T[Subscript C] Superconductor-Related Compounds , Xun-Li Wang Jan 1992

Neutron Diffraction Study Of The Electronic Structure Of High-T[Subscript C] Superconductor-Related Compounds , Xun-Li Wang

Retrospective Theses and Dissertations

Neutron diffraction techniques have been used to study the electronic structure of La[subscript]2NiO[subscript]4 and Sr[subscript]2CuO[subscript]2Cl[subscript]2 by measuring the antiferromagnetic form factor of the single-crystal samples at 15 K. The antiferromagnetic form factor was obtained from the integrated intensities of several magnetic reflections. In both cases, the experimentally determined form factor exhibits a plateau at low Q values (up to 3 A[superscript]-1), similar to that observed for La[subscript]2CuO[subscript]4. Detailed modelling of the experimental data of these three compounds suggests that the observed plateau may be ...


Phase Equilibria, Superconductivity, And Flux Creep In Nd1+[Subscript X]Ba2-[Subscript X]Cu3o7+[Subscript Delta] Superconductors , Sang-Im Yoo Jan 1992

Phase Equilibria, Superconductivity, And Flux Creep In Nd1+[Subscript X]Ba2-[Subscript X]Cu3o7+[Subscript Delta] Superconductors , Sang-Im Yoo

Retrospective Theses and Dissertations

NdBa[subscript]2Cu[subscript]3O[subscript]7 (Nd123) is one of REBa[subscript]2Cu[subscript]3O[subscript]7 (RE123) superconductors (RE = Y and rare earths), having the superconducting transition temperature (T[subscript] c) of about 90 K. From a processing standpoint, Nd123 is an interesting alternative to Y123 for applications because it exhibits both a higher peritectic decomposition temperature and a broader primary solidification range than Y123, and unlike Y123, the low temperature orthorhombic phase exists over a range of Nd compositions in Nd[subscript]1+xBa[subscript]2-xCu[subscript]3O[subscript]7+[delta] solid solution (Nd123ss) with little effect ...