Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X36: Glassy, Amorphous, and Quasicrystalline Materials |
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Sponsoring Units: DCMP Room: 408 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X36.00001: Using First-Principles Calculations to Describe Amorphous Metal Films for Hydrogen Purification Shiqiang Hao, Mike Widom, David Sholl The increasing demand for clean and efficient energy has resulted in an increased global willingness to embrace the proposed hydrogen economy. The use of amorphous metal films as membranes to purify hydrogen has potential to overcome at least some of the disadvantages of existing crystalline metal membranes. We introduce a general strategy combining density functional theory and statistical mechanics to quantitatively predict solubility, diffusivity and permeability of interstitial H in amorphous metals. Our methods make it possible for the first time to quantitatively evaluate the performance of amorphous metal films as hydrogen purification membranes. These methods are introduced by examining amorphous Fe3B and a crystalline analogue with the same composition. A membrane made from the amorphous material is predicted to have a hydrogen permeability 1.5-2 orders of magnitude higher than a crystalline membrane. The methods we introduce here will be useful in accelerating the development of amorphous membranes for practical applications. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X36.00002: Atomic structure of PdNiP bulk metallic glass from ab initio simulations Vijay Kumar, T. Fujita, M.W. Chen, A. Inoue, Y. Kawazoe The atomic structure of Pd40Ni40P20 bulk metallic glass (BMG) has been simulated using \textit{ab initio} molecular dynamics plane wave method and PAW pseudopotentials. We use generalized gradient approximation to calculate the exchange-correlation energy and a cubic simulation box whose size and shape have been optimized after the BMG has been formed in simulations. The resulting radial distribution function and density agree remarkably well with the experimental data. The structure is analysed in terms of local clusters centered around Pd, Ni and P atoms and their electronic structures have been used to understand the bonding, stability, and the formation of the PdNiP BMG. [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X36.00003: Role of Electronic Structure on Ductility of Iron-Based Bulk Metallic Glasses N. Kvaltine, X.J. Gu, S.J. Poon, G.J. Shiflet, M. Widom Composition effects on the mechanical properties of iron-based amorphous steel alloys have been investigated, with attention to the metalloid content and the relative impact of boron, carbon and phosphorous. Phosphorous-containing amorphous steels exhibited enhanced plastic strains and fracture strengths. Moreover, the plastic strain increased with the decrease in shear modulus. The shear moduli are appreciably lower than those reported for previous amorphous steel compositions that did not contain phosphorus, and the Poisson's ratios obtained are correspondingly high. The ductility of amorphous steels can be improved by chemically tuning the elastic properties which are determined by the amorphous structure and chemical bonding. First-principles electronic structure calculations show that ductility can be improved by partially replacing elements such as boron and carbon that create ionic and covalent bonds with other elements such as phosphorous that favor metallic cohesion. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X36.00004: Bond enthalpy trends of high metalloid Fe-based bulk metallic glasses M. Widom, B. Sauerwine, N. Kvaltine, X.J. Gu, S.J. Poon, G.J. Shiflet Chemical bond types in metal-metalloid glass-forming compounds range from metallic to ionic and covalent. Iron-rich alloys are dominated by metallic bonding, but charge transfer from iron atoms to highly electronegative metalloid elements such as boron, carbon and phosphorous creates ionicity, and the metalloid bonding is intrinsically covalent. For sufficiently large metalloid content their strong bonding character must increase the shear modulus, leading to an associated increase in brittleness of the material. However, for metalloid fractions below 30\%, shear modulus is found to decrease with increasing metalloid content, leading to an associated increase in ductility of the material. We show this unexpected decrease in shear modulus is caused by depletion of the charge density around the iron atoms, weaking the iron-iron bonds. Our calculations are based on Crystal Orbital Hamilton Populations (COHPs) for crystalline structures that locally approximate the amorphous structure. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X36.00005: Effect of excess electrons on hexagonal close-packed Mg and the model clusters for bulk metallic glasses Masae Takahashi, Mikio Fukuhara, Akihisa Inoue, Yoshiyuki Kawazoe Though empirical rules for a large glass forming ability (GFA) were proposed, the formation mechanism of the bulk metallic glasses (BMGs) and the main factors for the GFA have not been clearly elucidated. The advantages of Mg-based BMGs are the lightness and abundance of resources, and a wide supercooled liquid region with the very high thermal stability and extremely large GFA. In 1991, Inoue \textit{et al }developed glassy Mg--Cu--Y alloys with a maximum diameter of 4.0mm. We report here the effect of excess electrons on hexagonal close-packed Mg and the model clusters explained by an inflation process using density functional theory-based calculations, in order to understand the role of conduction electron concentration (CEC) in Mg-based BMGs [M. Takahashi et al,\textit{ J. Phys. D: Appl. Phys.,}\textbf{2008}, $41$, 155424]. The CEC of Mg increase in Mg-based BMGs. In our model calculations, the increased CEC is artificially realized by the injection of electrons into Mg clusters and hcp Mg. We find the volume expansion and distortion to a higher $c/a $ratio in the negative charge state. The increase in the values corresponding to the $c/a $ratio is also observed in the model clusters. In the density of states at the equilibrium cell parameters expanded by charging, the pseudogap near the Fermi level by $\sigma $--$\pi $ mixing becomes small and a spiky structure appears. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X36.00006: Toward Understanding the Giant Frictional Anisotropy on AlNiCo Keith McLaughlin, Heather Harper, David Rabson In a 2005 article in Science [{\bf309}, 1354], Park et al. measured in vacuum the friction between a coated atomic-force-microscope tip and the clean two-fold surface of an AlNiCo quasicrystal. Because the two-fold surface is periodic in one direction and aperiodic (with a quasiperiodicity related to the Fibonacci sequence) in the perpendicular direction, frictional anisotropy is not unexpected; however, the magnitude of that anisotropy in the Park experiment, a factor of 8, is unprecedented. By eliminating chemistry as a variable, the experiment also demonstrated that the low friction of quasicrystals must be tied in some way to their quasiperiodicity. Through molecular-dynamics simulations with pair potentials on quasiperiodic approximants, we investigate generic geometric mechanisms that might give rise to this anisotropy. [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X36.00007: Does the morphology of fracture surfaces reveal the structure of quasicrystals? Luc Barbier, Daniel Bonamy, Laurent Ponson The roughness of surfaces obtained by cleavage of i-AlPdMn quasicrystals at room temperature are analyzed using tools of quantitative fractography. From the atomic scale up to 3 nm, they are shown to exhibit scale invariance properties hiding the cluster (0.45 nm) aperiodic structure. These properties are quantitatively similar to those observed on various disordered materials, albeit on other ranges of length scales. These properties are interpreted as the signature of damage mechanisms occurring within a 3 nm wide zone at the crack tip. The size of this process zone finds its origin in the local temperature elevation at the crack tip. This effect is reported to be responsible for a transition from a perfectly brittle behavior to a nanoductile one. It explains also why the cluster structure of quasicrystals is not revealed on the fracture surfaces of i-AlPdMn broken at room temperature. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X36.00008: Quasicrystal Growth and Thermal Expansion Sally June Tracy, Jason Cooley, Heather Voltz, Jason Lashley We have grown Al-Mn-Pd and RE-MG-Zn quasicrystals (RE=Y, Er, Ho, Dy and Tb) from a high temperature metallic solution using a self-flux method with melt compositions presented in previous work by Canfield and Fisher.\footnote{High temperature solution growth of intermetallic single crystals and quasicrystals; Canfield, P.C. ; Fisher, I.R., Journal of Crystal Growth (May 2001) Vol. 255, is 2-4, p. 155-161} The samples showed dodecahedral grains with pentagonal facets. The icosahedral structure was revealed with x-ray powder diffraction. We were able to index the diffraction patterns using Cahn's two index scheme.\footnote{Indexing of icosahedral quasiperiodic crystals; Cahn, J.W. ; Shechtman, D. ; Gratias, D., Journal of Materials Research (Jan.-Feb.) vol. 1, no. 1, p. 13-26} We have measured the thermal expansion of these samples and will present this data. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X36.00009: Jamming is not just isotropic anymore E. Wandersman, Y. Chushkin, A. Robert, E. Dubois, V. Dupuis, R. Perzynski Slow dynamics observed in many disordered systems (colloidal glasses, jammed granular matter{\ldots}) are poorly understood. An approach could consist to discriminate the dynamical properties of such systems by the nature of the interaction potential (attractive/repulsive, isotropic/anisotropic). While the anisotropy of the potential is relevant for the rotational dynamics, its effect on the translational dynamics in glasses is quite absent of current understanding. We investigate here the effect of the interaction potential on the translational dynamics, in a magnetic colloidal glass (charge--stabilized magnetic nanoparticles). By applying a magnetic field H, the potential is tuned, from quasi-isotropic to anisotropic, but remains repulsive on average. The translational dynamics of the nanoparticles is probed (with/without field) using dynamical X-ray scattering [1]. Under field, anisotropic translational dynamics and aging are observed. Moreover, a strong anisotropic cooperativity is reported, almost hundred times larger in the parallel direction. The results are discussed using a phenomenological picture. ~ [1] E. Wandersman et. al., J. Phys. Cond. Mat. 20 (2007) 155104 [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X36.00010: Gradient interactions and the low temperature universality in glasses Moshe Schechter, Philip Stamp Amorphous solids show striking universal characteristics at low temperatures, including unique temperature dependencies of the specific heat, thermal conductivity and internal friction, and a small and rather constant ratio between a phonon wavelength and its mean free path. These universal phenomena are observed in polymers and disordered lattices as well. The standard tunneling model proposed by Anderson, Halperin and Varma, and Philips, accounts well for much of the observed phenomena. However, questions regarding the nature of the two-level systems, the smallness of the above ratio, and the energy scale dictating the temperature range of the phenomena, remain unanswered. We propose a theory that suggests an answer to these questions, along with an explanation of the additional observed phenomena connected with the universal behavior. Our theory is rigorously derived for disordered lattices, and we argue for the plausibility of its applicability to amorphous solids. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X36.00011: Moment based approach to electronic structure calculations: applications to ordered and disordered systems Hiro Shimoyama, Parthapratim Biswas We solve the classical moment problem via maximum entropy optimization to calculate the electronic density of states for ordered and disordered solids. The method employs the Shannon entropy functional and maximize it subject to the moment constraints to construct the spectral distribution of large Hamilton matrix. We illustrate the efficiency and usefulness of the method by applying three candidate systems: a crystalline semiconductor; an amorphous material; and a completely disordered system via tight-binding Anderson model Hamiltonian. The band energy and Fermi level are computed from the reconstructed density of states with a high degree of precision. A possible extension of this method to calculate electronic forces is also discussed. [Preview Abstract] |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X36.00012: Reciprocal-Space Approach of Highly Inhomogeneous Systems Volodymyr Bugaev, Alexander Udyansky, Thomas Demmer, Alejandro Diaz Ortiz, Peter Wochner, Helmut Dosch A reciprocal-space approach for the calculation of spatial correlations in highly inhomogeneous systems is presented. Our method is based on the correlation-correction algorithm\footnote{V.N.\ Bugaev, A.\ Udyansky, O.\ Shchyglo, H.Reichert, and H.\ Dosch, Correlation correction algorithm for disordered binary systems, Phys.\ Rev.\ B {\bf 74}, 024202 (2006)} and can also be used in the calculation of thermodynamic potentials of metallic and colloidal glasses. The interaction parameters are calculated in an iterative $k$-space (refinement) procedure that is amenable for both first-principles and semi-empirical calculations. We illustrate our approach on amorphous hard-sphere and Lennard-Jones systems. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X36.00013: What is a dynamical glass transition? Claudio Chamon, Claudio Castelnovo, David Sherrington Using the mapping between the Fokker-Planck description of classical stochastic dynamics into a quantum Hamiltonian, we argue that a dynamical glass transition must have a precise definition in terms of a quantum phase transition. At the static level, the transition affects the ground state wavefunction: while in some cases it could be picked up by the expectation value of a local operator, in others the order may be non-local, and impossible to be determined with any local probe. In general, even in the absence of a local order parameter, the transition can be detected via the quantum fidelity of the groundstate wavefunction, which we show translates directly into a singularity in the heat capacity of the classical system. We illustrate these ideas using exact diagonalizations of the mapped Hamiltonians for the p-spin models and the gonihedric model. [Preview Abstract] |
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