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Full-Text Articles in Physics

Dynamical Diffraction And X-Ray Standing Waves From Atomic Planes Normal To A Twofold Symmetry Axis Of The Quasicrystal Alpdmn, Terrence Jach, Y. Zhang, R. Colella, M. De Boissieu, Alan I. Goldman, Thomas A. Lograsso, D. W. Delaney, S. Kycia Apr 1999

Dynamical Diffraction And X-Ray Standing Waves From Atomic Planes Normal To A Twofold Symmetry Axis Of The Quasicrystal Alpdmn, Terrence Jach, Y. Zhang, R. Colella, M. De Boissieu, Alan I. Goldman, Thomas A. Lograsso, D. W. Delaney, S. Kycia

Ames Laboratory Publications

We have observed dynamical diffraction in the [[(02402̅ 4) and [[(04604̅ 6) reflections of the icosahedral quasicrystal AlPdMn in the back-reflection geometry ( θB = 90°). The x-ray fluorescence from the Al and Pd atoms exhibits strong standing wave behavior, similar to that observed in crystalline materials. The data indicate a long-range order of each species of atoms, with the coherent positions attributable to distributions of the Al and Pd, which we compare to a centrosymmetric model. We observe deviations from the model which imply small departures from inversion symmetry along the twofold symmetry axis and from the expected coherent fractions ...


Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel Oct 1998

Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel

Chemistry Publications

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below ∼700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for ...


Clustered, Terraced And Mixed Surface Phases Of The Al70pd21mn9 Quasicrystal, J. Ledieu, A. W. Munz, T. M. Parker, R. Mcgrath, R. D. Diehl, Dwight W. Delaney, Thomas A. Lograsso Jan 1998

Clustered, Terraced And Mixed Surface Phases Of The Al70pd21mn9 Quasicrystal, J. Ledieu, A. W. Munz, T. M. Parker, R. Mcgrath, R. D. Diehl, Dwight W. Delaney, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

The five-fold surface of the Al70 Pd21 Mn9 quasicrystal has been studied using STM, LEED and AES. STM images from surfaces which have been sputtered and annealed to 875 K reveal 20-30 Å protrusions that have been identified by others as Mackay-type clusters. Higher-resolution images reveal substructures in these clusters having dimensions 2-3 Å. Longer annealing times at 875 K produced large areas having flat terraces which were imaged with atomic resolution. The LEED pattern from this surface has sharp spots on a low background, and AES indicates that the surface is deficient in Mn relative to ...


Generalization Of Hysteresis Modeling To Anisotropic Materials, A. Ramesh, David C. Jiles, Y. Bi Apr 1997

Generalization Of Hysteresis Modeling To Anisotropic Materials, A. Ramesh, David C. Jiles, Y. Bi

Materials Science and Engineering Publications

An extension to the model of hysteresis has been presented earlier which included the effect of anisotropy in the modeling of the anhysteretic magnetization curves of uniaxially anisotropic single crystalline materials. Further exploration of this extension shown here considers different kinds of crystal anisotropy in materials. Theory considers that the differential susceptibility at any given field is determined by the displacement of the prevailing magnetization from the anhysteretic magnetization. Thus, it has been shown that the effect of anisotropy on magnetic hysteresis in materials can be incorporated into the model of hysteresis through the anisotropic anhysteretic. This extension is likely ...


Structure And Stability Of The Twofold Surface Of Icosahedral Al-Pd-Mn By Low-Energy Electron Diffraction And X-Ray Photoemission Spectroscopy, Z. Shen, Cynthia J. Jenks, James W. Anderegg, D. W. Delaney, Thomas A. Lograsso, Patricia A. Thiel, A. I. Goldman Feb 1997

Structure And Stability Of The Twofold Surface Of Icosahedral Al-Pd-Mn By Low-Energy Electron Diffraction And X-Ray Photoemission Spectroscopy, Z. Shen, Cynthia J. Jenks, James W. Anderegg, D. W. Delaney, Thomas A. Lograsso, Patricia A. Thiel, A. I. Goldman

Ames Laboratory Publications

We have used low-energy electron diffraction and x-ray photoemission spectroscopy to investigate the structure of the twofold surface of icosahedral Al-Pd-Mn. The regrowth of the surface by annealing after sputtering took place in two distinct stages. The first stage was the appearance of a fine-grained surface phase with icosahedral, or near-icosahedral, symmetry. For higher annealing temperatures (above 800 K) a bulk terminated face-centered icosahedral surface was observed.


Hydrogen Charging In Nickel And Iron And Its Effect On Their Magnetic Properties, A. Ramesh, Madhav Rao Govindaraju, David C. Jiles, S. B. Biner, J. M. Roderick Apr 1996

Hydrogen Charging In Nickel And Iron And Its Effect On Their Magnetic Properties, A. Ramesh, Madhav Rao Govindaraju, David C. Jiles, S. B. Biner, J. M. Roderick

Materials Science and Engineering Publications

The current study was undertaken to explore the possibility of detecting hydrogen cavitation in magnetic materials through magnetic propertymeasurements. It is known that dissolved hydrogen in a material causes microvoids. These voids may affect the structure‐sensitive magnetic properties such as coercivity and remanence. In this study, hydrogen was introduced into nickel and iron by two processes, namely thermal charging and cathodic charging. The effect on the magnetic properties was measured. In addition, the variation of the magnetic properties with porosity was studied.


Reply To ‘‘Comment On ‘Correlation Functions For Ionic Motion From Nmr Relaxation And Electrical Conductivity In The Glassy Fast-Ion Conductor (Li2s)0.56(Sis2)0.44’ ’’, Ivar Svare, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin May 1995

Reply To ‘‘Comment On ‘Correlation Functions For Ionic Motion From Nmr Relaxation And Electrical Conductivity In The Glassy Fast-Ion Conductor (Li2s)0.56(Sis2)0.44’ ’’, Ivar Svare, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin

Materials Science and Engineering Publications

Hunt’s Comment criticizes our recent article for combining concepts from percolation theory and effective-medium theories to calculate the dc and ac conductivities in ionic conducting glasses. Our approach was an attempt to describe the dc and ac conductivity with input information from our NMR measurements. We used the continuous-time random-walk theory and reasonable assumptions for the glasses which yielded good fits of the dc and ac conductivities at many temperatures.


Estimation Of The Free-Charge-Carrier Concentration In Fast-Ion Conducting Na2s-B2s3 Glasses From An Analysis Of The Frequency-Dependent, Ernest F. Hairetdinov, Nikolai F. Uvarov, Hitendra K. Patel, Steve W. Martin Nov 1994

Estimation Of The Free-Charge-Carrier Concentration In Fast-Ion Conducting Na2s-B2s3 Glasses From An Analysis Of The Frequency-Dependent, Ernest F. Hairetdinov, Nikolai F. Uvarov, Hitendra K. Patel, Steve W. Martin

Materials Science and Engineering Publications

ac and dc conductivities of fast-ion conducting xNa2S+(1-x)B2S3 glasses in the composition range 0.001≤x≤0.1 were analyzed using the Almond-West formula σ(ν)=σdc[1+(ν/νH)α]. The hopping frequency for free charge carriers νH, the dc conductivity σdc, and their respective activation energies were determined. The concentration of free charge carriers evaluated from the conductivities and estimated mobilities is in good agreement with the overall content of sodium cations in the glasses and it is proposed that this supports the concept of a strong and not weak electrolyte model for these ...


Elastic Constants Of Bcc Cu-Al-Ni Alloys, Lluís Mañosa, M. Jurado, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, C. Stassis Apr 1994

Elastic Constants Of Bcc Cu-Al-Ni Alloys, Lluís Mañosa, M. Jurado, Antoni Planes, Jerel L. Zarestky, Thomas A. Lograsso, C. Stassis

Ames Laboratory Publications

We have measured the adiabatic elastic constants of two Cu-Al-Ni martensitic alloys using ultrasonic methods and we have compared the results to recent neutron-scattering experiments. It is shown that the elastic behavior of Cu-Al-Ni alloys follows the same trends exhibited by other Cu-based alloys; in particular, the TA2 long-wavelength acoustic modes are softer than all other modes.


Lattice-Dynamical Study Of The Premartensitic State Of The Cu-Al-Be Alloys, Lluís Mañosa, Jerel L. Zarestky, Thomas A. Lograsso, Dwight W. Delaney, C. Stassis Dec 1993

Lattice-Dynamical Study Of The Premartensitic State Of The Cu-Al-Be Alloys, Lluís Mañosa, Jerel L. Zarestky, Thomas A. Lograsso, Dwight W. Delaney, C. Stassis

Ames Laboratory Publications

Neutron-scattering techniques have been used to study the premartensitic state of a family of Cu-Al-Be alloys, which transform from the bcc phase to an 18R martensitic structure. We find that the phonon modes of the TA2[110] branch have very low energies with anomalous temperature dependence. A slight anomaly at q=2/3 was observed; this anomaly, however, does not change significantly with temperature. No elastic peaks, related to the martensite structure, were found in the premartensitic state of these alloys. The results are compared with measurements, performed under the same instrumental conditions, on two Cu-Al-Ni and a Cu-Zn-Al ...


Correlation Functions For Ionic Motion From Nmr Relaxation And Electrical Conductivity In The Glassy Fast-Ion Conductor (Li2s)0.56(Sis2)0.44, Ivar Svare, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin Oct 1993

Correlation Functions For Ionic Motion From Nmr Relaxation And Electrical Conductivity In The Glassy Fast-Ion Conductor (Li2s)0.56(Sis2)0.44, Ivar Svare, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin

Materials Science and Engineering Publications

The Li7 NMR spin-lattice relaxation and the electrical conductivity in the typical glassy fast-ion conductor (Li2S)0.56(SiS2)0.44 are discussed from models of Li+ionic motion with distributions of activation energies, as well as from stretched-exponential time-correlation functions. The measured correlation times from the two effects differ by two orders of magnitude, and the derived distributions are shifted greatly relative to each other. We relate the great differences to percolation around the high barriers in the distribution. We present a phenomenological theory that yields good quantitative fits to the observed NMR relaxation with a Gaussian distribution, and ...


Dynamical X-Ray Diffraction From An Icosahedral Quasicrystal, S. W. Kycia, Alan I. Goldman, Thomas A. Lograsso, Dwight W. Delaney, D. Black, M. Sutton, E. Dufresne, R. Brüning, B. Rodricks Aug 1993

Dynamical X-Ray Diffraction From An Icosahedral Quasicrystal, S. W. Kycia, Alan I. Goldman, Thomas A. Lograsso, Dwight W. Delaney, D. Black, M. Sutton, E. Dufresne, R. Brüning, B. Rodricks

Ames Laboratory Publications

We present direct evidence of dynamical diffraction of x rays from a quasicrystal. High-resolution x-ray-diffraction measurements of the Al-Pd-Mn face-centered icosahedral quasicrystal were performed, revealing a mosaic full width at half maximum of less than 0.001°. In a second experiment, the anomalous transmission of x rays (the Borrmann effect) was observed. These measurements show that nearly perfect quasicrystals may be grown to centimeter-size dimensions allowing x-ray techniques based upon dynamical diffraction to be brought to bear on the analysis of icosahedral structures.


Modeling Of Micromagnetic Barkhausen Activity Using A Stochastic Process Extension To The Theory Of Hysteresis, David C. Jiles, Levent B. Sipahi, G. Williams May 1993

Modeling Of Micromagnetic Barkhausen Activity Using A Stochastic Process Extension To The Theory Of Hysteresis, David C. Jiles, Levent B. Sipahi, G. Williams

Materials Science and Engineering Publications

Recent work by Bertotti [IEEE Trans. Magn. MAG‐24, 621 (1988)] and others has shown that it is possible to model the micromagnetic Barkhausen discontinuities at the coercive point using a two‐parameter stochastic model. However, the present formulation of the model is restricted to limited regions of the hysteresis curve over which dM/dH is approximately constant and whendH/dt is held at a constant rate. A natural extension of this model is to take the basic result, in which the level of Barkhausen activity in one time period is related to the activity in the previous time ...


Comprehensive Analysis Of Barkhausen Emission Spectra Using Pulse Height Analysis, Frequency Spectrum, And Pulse Wave Form Analysis, Levent B. Sipahi, David C. Jiles, D. Chandler May 1993

Comprehensive Analysis Of Barkhausen Emission Spectra Using Pulse Height Analysis, Frequency Spectrum, And Pulse Wave Form Analysis, Levent B. Sipahi, David C. Jiles, D. Chandler

Materials Science and Engineering Publications

The dependence of magnetic Barkhausen emissions (MBE) upon both field excitation and detection frequencies and excitation wave form was studied in order to investigate two of several crucial factors which affect the emissions. Sinusoidal, triangular, and square wave forms were used to generate the MBE and the pulse height spectra, frequency spectra, and pulse wave forms of these signals were analyzed. The frequency spectra of sinusoidal and triangular alternating field excitations showed similar behavior but the spectrum under square wave excitation was different due to the existence of high frequency components during square wave switching. As yet, no common standard ...


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 ...


Structure Of Au And Pt Films On Pd(110): Deposition Temperature And Coverage Dependent (1 X 2) And (1 X 3) Reconstructions, P. J. Schmitz, H.-C. Kang, W.-Y. Leung, Patricia A. Thiel Jan 1991

Structure Of Au And Pt Films On Pd(110): Deposition Temperature And Coverage Dependent (1 X 2) And (1 X 3) Reconstructions, P. J. Schmitz, H.-C. Kang, W.-Y. Leung, Patricia A. Thiel

Ames Laboratory Publications

We present the results of a LEED study of the structures of Au and Pt films grown on Pd(110). We observe both (1x2) and (1x3) overlayer structures depending upon the coverage and deposition temperature. We explain the coverage and deposition temperature dependence of these reconstructions in terms of basic factors which control film growth processes.


Correlation Between The Activation Enthalpy And Kohlrausch Exponent For Ionic Conductivity In Oxide Glasses, Kia L. Ngai, Steve W. Martin Nov 1989

Correlation Between The Activation Enthalpy And Kohlrausch Exponent For Ionic Conductivity In Oxide Glasses, Kia L. Ngai, Steve W. Martin

Materials Science and Engineering Publications

We have established for alkali ions in oxide glasses a strong correlation between the fractional (Kohlrausch) exponent β in the conductivity relaxation function, exp[-(t/τ*)β], and the activation energy E*a of τ* and σ when varying the composition of oxide glass formers and the alkali ions while holding the alkali-ion concentration constant. An even stronger correlation of the trends in β and the product βE*a is found. These correlations were expected conceptually by the coupling model for conductivity relaxation, and the latter was the motivation behind the present undertaking of the establishment of the correlation from ...


The Resistivity And Microstructure Of Heavily Drawn Cu‐Nb Alloys, J. D. Verhoeven, H. L. Downing, L. Scott Chumbley, E. D. Gibson Jan 1989

The Resistivity And Microstructure Of Heavily Drawn Cu‐Nb Alloys, J. D. Verhoeven, H. L. Downing, L. Scott Chumbley, E. D. Gibson

Materials Science and Engineering Publications

A combined resistivitytransmission electron microscopy(TEM) study has been done on heavily drawn Cu‐20 vol % Nb alloys (so‐called i n s i t u alloys). The results show that electron scattering at Cu‐Nb interfaces makes the major contribution to resistivity in heavily drawn wire. The dislocation contribution is small and constant at deformation strains greater than around 4, apparently as a result of dynamic recovery/recrystallization of the Cu matrix which occurs during room‐temperature drawing. Results of this study and other recent TEM dislocation studies indicate that the dislocation density in heavily drawn Cu‐20 vol ...


An Electron Channeling Study Of Polycrystalline Yba2cu3o X, J. D. Verhoeven, E. D. Gibson, L. Scott Chumbley, R. William Mccallum, H. H. Baker Jul 1988

An Electron Channeling Study Of Polycrystalline Yba2cu3o X, J. D. Verhoeven, E. D. Gibson, L. Scott Chumbley, R. William Mccallum, H. H. Baker

Materials Science and Engineering Publications

An electron channeling study has been done on large grained YBa2Cu3O x samples. Selected area channeling patterns (SACP) were used to examine several dozen grains on electropolished surfaces and it was demonstrated that (a) the twin planes observed in polarized optical light microscopy lie parallel to {110} crystal planes, and (b) the long flat sides of high aspect ratio grains are formed by basal planes, and the shorter sides are formed by either (010), (100), or {110} planes. A majority of the large grains examined were found to contain subgrains, misaligned by 0.5°–1° and ...


Possible Twin-Boundary Effect Upon The Properties Of High-Tc Superconductors, M. M. Fang, Vladimir G. Kogan, Douglas K. Finnemore, J. R. Clem, L. Scott Chumbley, D. K. Farrell Feb 1988

Possible Twin-Boundary Effect Upon The Properties Of High-Tc Superconductors, M. M. Fang, Vladimir G. Kogan, Douglas K. Finnemore, J. R. Clem, L. Scott Chumbley, D. K. Farrell

Materials Science and Engineering Publications

We have studied the field at which superconductivity nucleates in grain-aligned samples of Y1Ba2Cu3O7-δ very close to the transition temperature Tc. For the field parallel to the c axis and for temperatures within 2 K of Tc, the nucleation field is found to vary as (1-T/Tc)1/2. The data suggest that superconductivity localized near twin boundaries may exist at temperatures close to Tc. .AE


A Comparison Of Multiple Frequency And Pulsed Eddy Current Techniques, W. E. Deeds Jan 1979

A Comparison Of Multiple Frequency And Pulsed Eddy Current Techniques, W. E. Deeds

Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE, July 1977–June 1978

In principle, the same information should be obtainable from. either pulsed or multiple frequency eddy current techniques, provided they utilize comparable frequency ranges. In practice, there are important differences and advantages for each method. Pulse instrumentation is generally cheaper, simpler, and less sophisticated. On the other hand, there has been greater development of theory and instrumentation using sinusoidal eddy currents, so that the equipment is generally more quantitative at present. The basic problem of determining certain paramenters when others may also be varying can be solved by measuring enough quantities to eliminate the unwanted variables, for example, by measuring the ...


Secondary Electron Emission Due To Positive Ion Bombardment, John W. Murdock, Glenn H. Miller Jun 1955

Secondary Electron Emission Due To Positive Ion Bombardment, John W. Murdock, Glenn H. Miller

Ames Laboratory ISC Technical Reports

Stray electrons were produced in the Ames Laboratory linear accelerator by the ion beam striking the target and various other parts of the accelerator. This experiment was done to determine if the stray electrons from parts of the accelerator other than the target could be reduced by using construction materials other than brass. Measurements of the number of electrons produced from several materials, however, indicated that there is no particular advantage in using other materials in place of brass.


Thermal Conductivity Of Metals At High Temperatures, Paul H. Sidles, G. C. Danielson Dec 1951

Thermal Conductivity Of Metals At High Temperatures, Paul H. Sidles, G. C. Danielson

Ames Laboratory ISC Technical Reports

A new method of measuring thermal diffusivity and hence thermal conductivity of metals is suggested. Like previously reported dynamic methods, this method uses a heat source, whose temperature varies sinusoidally located at one end of an effectively infinite rod. Unlike these methods only one period of the heat wave is required to eliminate the unknown coefficient determining the heat lost by radiation since both velocity and amplitude decrement of the heat wave are measured. The new method is faster in taking data and simpler in computation. The thermoelectric potentials from two thermojunctions are amplified and plotted on a Brown "Electronic ...