Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X31: Amorphous Solids, Glasses & Liquids I |
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Sponsoring Units: DCMP Chair: Punit Boolchand, University of Cincinnati Room: C145 |
Thursday, March 24, 2011 2:30PM - 2:42PM |
X31.00001: Evidence of Fatigue Damage in the Local Structure of Zr-based Bulk Metallic Glasses Despina Louca, Peng Tong, Peter Liaw, Gongyao Wang, Yoshihiko Yokoyama, Anna Llobet, Rick Spence Bulk metallic glasses (BMG) are particularly vulnerable to fatigue damage, where catastrophic failure may occur without observable macroscopic changes. The local atomic structure of two BMGs with compositions of Zr$_{50}$Cu$_{40}$Al$_{10}$ and Zr$_{60}$Cu$_{30}$Al$_{10 }$was investigated by synchrotron X-ray and neutron diffraction via the pair density function analysis. Under a load of 1600 MPa, the number of compression cycles ranged from 0 -- 10$^{7}$ at 10 Hz. At room temperature, a subtle but irreversible change is observed in the local structure due to fatigue. Upon cooling down to 10 K, however, a significant structural re-organization is observed especially in the short range that is proportional to the number of fatigue cycles. The effect becomes more pronounced with increasing the number of loading cycles. The changes are beyond the usual narrowing from reducing thermal vibrations. The results indicate that hardening occurs after fatigue. [Preview Abstract] |
Thursday, March 24, 2011 2:42PM - 2:54PM |
X31.00002: Analysis of Amorphous Iron Surface Energies and Bulk Properties using DFT Charles Newnam, Michael Mehl, Daniel Finkenstadt From Ab Initio calculations, we compare the energy of amorphous Iron to bcc and fcc Iron structures, both at zero pressure and high pressure. From these calculations we draw conclusions on the properties of metallic glass structures over a range of pressure. Additionally, we address the adsorption energy of Oxygen on amorphous surfaces versus the structure's cell size and compared against bcc and fcc Iron structures. The adsorption energies allow us to evaluate the corrosion potential of an amorphous structure versus a typical crystalline surface. [Preview Abstract] |
Thursday, March 24, 2011 2:54PM - 3:06PM |
X31.00003: Super-localization of atomic dynamics in liquid Iron Madhusudan Ojha, David J. Keffer, Don M. Nicholson, Takeshi Egami Lattice dynamics in crystals is well described in terms of phonons. However, phonons cannot give precise description of the atomic dynamics in liquids because they are highly damped. We carried out MD simulations of liquid iron at high temperatures. The results are presented in terms of the dynamic pair-density function (DPDF), which describes the atomic correlation, or the distribution of atomic distances over time, at the angular frequency $\omega $. Our analysis shows that the atomic dynamics in liquid iron above the boson mode (BM) is confined to only the nearest neighbors, resulting in super-localization of atomic dynamics. The dynamics of nearest neighbor shells is well described in terms of atomic level stresses. This super-localization of atomic dynamics in liquid iron implies that the dynamics of the local atomic level stresses represents the normal modes in liquids at high temperatures, and justifies the equipartition law observed for the atomic level stresses [1]. \\[4pt] [1] V. Levashov, et al. Phys. Rev. B 78,064205 (2008) [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:18PM |
X31.00004: Data-mining for hidden order in metallic liquids and glasses Xiaowei Fang, C.Z. Wang, Y.X. Yao, Z.J. Ding, K.M. Ho Although metallic liquids and glasses look quite homogenous macroscopically, most of them exhibit structural and chemical orders at the atomic scale. This short-range (SRO) or medium-range order (MRO) occurs on a length scale of 5-20 {\AA}. However, they are generally difficult to discern at the macroscopic scale due to random orientations of the ordered units. In this paper, we develop an efficient computational algorithm to align the neighborhood cluster around each atom to reveal the hidden symmetry and order contained in the system. In our alignment algorithm, we put the center atoms into a common origin and rigidly rotate the clusters to maximize their common registry to reveal any existing SRO or MRO. The results determine what are the major competing orders and the strengths of various orders in the system. Such atomic scale information are very difficult to acquire by experiments and are critical for understanding the mechanism of glass formation and phase selections during the rapid solidification from the metallic liquids. [Preview Abstract] |
Thursday, March 24, 2011 3:18PM - 3:30PM |
X31.00005: Metallic States of Multicomponent Glasses Terrence Jach The K$\alpha _{3}$ and K$\alpha _{4}$ satellite lines in x-ray fluorescence result from two-electron shake-up transitions. The ratio of these lines in some solids is known to be highly sensitive to the valence band of the material and a well-defined indicator of metallic vs. oxide states. The good energy resolution of a microcalorimeter x-ray detector allows us to determine the ratio in the fluorescence x-ray spectrum of glasses. An investigation of the satellite ratios of Mg and Al K$\alpha $ lines in a multi-component glass used as a NIST Standard Reference Material shows that these elements appear to be in a metallic state, despite the original constituents of the glass. This result would be hard to determine by x-ray photoemission spectroscopy because of charging effects in the glass. It remains to be determined whether the effect is due merely to incomplete oxidation of the atoms or actual nanoparticle-sized metallic phases in the glass. [Preview Abstract] |
Thursday, March 24, 2011 3:30PM - 3:42PM |
X31.00006: An NMR study of homogenous deformation-induced ordering in La$_{50}$Ni$_{15}$Al$_{35 }$ Magdalena Sandor, Yue Wu, Haibo Ke, Wei Hua Wang The mechanism of mechanical deformation is currently an unresolved issue of fundamental importance. $^{27}$Al NMR nutation experiments in La$_{50}$Ni$_{15}$ Al$_{35}$ bulk metallic glasses (BMG) were carried out to probe local structural changes induced by elastostatic compression at room temperature. It was observed that compression enhances local symmetry at Al sites with compression time. Modulated differential calorimetry studies were also performed to understand how free volume changes with compression time. Results provide insight into the nature of homogenous deformation and the interplay of free volume with local structural changes. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X31.00007: Understanding intrinsic ductility from Poisson's ratio for amorphous solids through force-field tuning Yunfeng Shi, Jian Luo This work is motivated by recently observed empirical relationship between the Poisson's ratio and the fracture energy for a range of metallic glasses and oxide glasses. Glassy solids with low Poisson's ratio are brittle and vice versa, with a critical Poisson's ratio of about 0.31. Here we used a force-field tuning scheme to investigate how a near-equilibrium elastic constant determines far-from-equilibrium fracture behavior. By modifying a well-studied binary Lennard-Jones system, we obtained a family of glassy systems with different Poisson's ratio ranging from 0.2 to 0.4. Interestingly, the model glasses with low Poisson's ratio exhibit brittle fracture in tension and vice versa, which agrees with experimental observations. Finally, we will discuss how ductility of amorphous solids can be comprehended in terms of the structure and bonding of the amorphous solids, both of which also dictate the Poisson's ratio. [Preview Abstract] |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X31.00008: Universal Sound Attenuation in Amorphous Solids Dervis Can Vural A large class of amorphous materials, including glasses, polymers, disordered crystals and in some cases quasi-crystals and proteins, show a striking degree of universality in their low temperature acoustic and thermal properties. Among the least understood is the dimensionless acoustic mean path $l/\lambda \sim 150$. Although many theories have been proposed to explain the universality of this constant, they rely on detailed phenomenological assumptions, such as the existence of tunneling two-state systems. In this talk, I present the many-body acoustic response of elastically coupled random matrices to demonstrate that the universality is a property of a general class of theories, and emerges regardless of the detailed assumptions regarding the constituents of the amorphous solid. [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X31.00009: Finite-temperature critical point of a glass transition Yael Elmatad, Robert Jack, Juan Garrahan, David Chandler We generalize the simplest kinetically constrained models of a glass-forming liquid by softening kinetic constraints, allowing them to be violated with a small rate. We demonstrate that these models support a first-order dynamical (space-time) phase transition between active (fluid) and inactive (glass) phases. The first-order phase boundary in these softened model ends in a finite-temperature dynamical critical point, which may be present in natural systems. In this case, the glass phase has a very large but finite relaxation time. We discuss links between the dynamical critical point and quantum phase transitions, showing that dynamical phase transitions in $d$ dimensions map to quantum transitions in the same dimension, and hence to classical thermodynamic phase transitions in $d + 1$ dimensions. [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X31.00010: Nonequilibrium relaxation and aging scaling properties of the Coulomb glass Matthew T. Shimer, Uwe C. T\"auber, Michel Pleimling Using Monte Carlo simulations, we analyze the two-time density autocorrelation function for the two- and three-dimensional Coulomb glass with various long-range interaction potentials. A full aging scaling ansatz is sufficient to describe the nonequilibrium relaxation properties of these highly correlated disordered systems. By investigating the trends of the scaling exponents, we find that they are non-universal, and depend on temperature, charge density, and interaction strength. \par \noindent Reference: EPL {\bf 91}, 67005 (2010). [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X31.00011: Vibrational excitations and elastic phases in Sodium Borate Glasses K. Vignarooban, P. Boolchand, M. Micoulaut Glass Transition temperatures (T$_g$s) and non-reversing enthalpy ($\Delta$H$_{nr}$) at T$_g$ of dry (Na$_2$O)$_x$(B$_2$O$_3$)$_{100-x}$ glasses across the 0\% $<$ x $<$ 44\% soda range are measured. Trends in $\Delta$H$_{nr}$(x) show a reversibility window in the 20\% $<$ x $<$ 40\% range, and fix the Intermediate Phase (IP). IR and Raman vibrational modes including Boson modes are also examined. At low x ($<$ 20\%), the Raman active 808 cm$^{-1}$ mode of boroxyl rings steadily lowers in scattering strength and red-shifts with increasing x, suggesting that the stressed-rigid quasi 2D network of B$_2$O$_3$ glass at x = 0, steadily softens with a characteristic optical elastic power-law (p$_1$ = 0.85(2)). In the 26\% $<$ x $<$ 40\% range, a mode near 770 cm$^{-1}$ rapidly grows in strength and red shifts with increasing x with a power- law of p$_2$= 1.05(5) characteristic of IPs observed earlier$^a$ in other 3D covalent and ionic networks. In addition, many other modes are observed, some blue-shift, some red-shift and some remain unchanged with x. These data will be discussed in relation to glass structure evolution with composition.\\[4pt] D.Novita et al. J. Phys. Condens. Matter 21, 205106 (2009) [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 4:54PM |
X31.00012: Accelerated kinetics of amorphous silicon using an on-the-fly off-lattice kinetic Monte-Carlo method Jean-Francois Joly, Fedwa El-Mellouhi, Laurent Karim Beland, Normand Mousseau The time evolution of a series of well relaxed amorphous silicon models was simulated using the kinetic Activation-RelaxationTechnique (kART), an on-the-fly off-lattice kinetic Monte Carlo method [1]. This novel algorithm uses the ART nouveau algorithm to generate activated events and links them with local topologies. It was shown to work well for crystals with few defects but this is the first time it is used to study an amorphous material. A parallel implementation allows us to increase the speed of the event generation phase. After each KMC step, new searches are initiated for each new topology encountered. Well relaxed amorphous silicon models of 1000 atoms described by a modified version of the empirical Stillinger-Weber potential [2] were used as a starting point for the simulations. Initial results show that the method is faster by orders of magnitude compared to conventional MD simulations up to temperatures of 500 K. Vacancy-type defects were also introduced in this system and their stability and lifetimes are calculated. \\[4pt] [1] El-Mellouhi et al., ,Phys Rev. B, 78, 153202 (2008)\\[0pt] [2] Vink et al., J. Non-Cryst. Sol. 282, 248 (2001) [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:06PM |
X31.00013: ABSTRACT WITHDRAWN |
Thursday, March 24, 2011 5:06PM - 5:18PM |
X31.00014: Properties of fluids under strong confinement: a mode coupling approach Saroj Nandi, Sarika Bhattacharya, Sriram Ramaswamy We extend the mode coupling theory (MCT) of glass transition in bulk fluids to the case of confinement, which enhances the feedback mechanism to drive the system to a glassy state. Confinement enters the theory in terms of an external potential that produces an inhomogeneous density background, which in turn forces the fluid to relax diffusively. Below a certain density, the MCT transition becomes continuous and the critical density of continuous to discontinuous transition depends on the nature of the external potential. If the control parameters are in the proper region of phase space, the fluid shows a three-step relaxation scenario. We also incorporate shear in our theory and thereby show that the fluid, when confined, shows shear thinning at much lower shear rate compared to a bulk fluid. [Preview Abstract] |
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