Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P23: Lattice and Mechanical Properties |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Daniel Finkenstadt, University of Illinois at Urbana-Champaign Room: 325 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P23.00001: Temperature dependence of the phonon density of states in FeSi and CoSi. Olivier Delaire, Matthew Lucas, Matthew Stone, Douglas Abernathy The phonon density of states (DOS) of the B20 compounds Fe(1-x)Co(x)-Si (x=0.0, 0.03, 0.5, 1.0) was measured as function of temperature from 10K to 773K using inelastic neutron scattering. The phonon DOS of FeSi exhibits an excess softening compared to the predictions of the quasiharmonic model, in agreement with previous measurements of elastic constants as function of temperature [1]. The phonon DOS of CoSi softens less, on the other hand, and appears in better agreement with the pure volume effect of the quasiharmonic model. These trends are compared to previous measurements of the temperature dependence of the phonon DOS in the A15 compounds V3Si and V3Ge [2]. Using first-principles electronic structure calculations, the observed anomalies are related to the details of the band structure in these compounds. It is shown that sharp features in proximity to the Fermi level lead to anomalous phonons through a sensitivity to thermal disorder, or adiabatic electron-phonon coupling. [1] D. Mandrus et al., Phys. Rev. B 51, 4763 (1994) [2] O. Delaire et al. , Phys. Rev. Lett. 101, 105504 (2008) [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P23.00002: Effects of temperature and chemical order on phonons in Fe-V alloys Matthew Lucas, Jorge Munoz, Olivier Delaire, Brent Fultz, Douglas Abernathy, Matthew Stone, Mark Loguillo Inelastic neutron-scattering spectra were measured on body-centered-cubic Fe-V alloys as a function of temperature and composition. These data were reduced from time-of-flight histograms to spectra that resemble the phonon density of states (DOS), but were distorted by differences in efficiencies of the atom species for phonon scattering. Nuclear resonant inelastic x-ray scattering spectra were measured for the 57-Fe isotope in a similar set of alloys at room temperature to compliment the neutron spectra. With temperature the 50-50 alloy undergoes an ordering transition from A2 to B2, as evidenced by increasing intensity in the superlattice peaks from the elastic regime of the neutron spectra. This ordering is accompanied by a change in the phonon DOS. The Connolly-Williams cluster inversion method is performed on the DOS of the disordered Fe-V alloys in order to correlate changes in the chemical order with changes in the DOS for the 50-50 alloy. The temperature dependence of the DOS of the disordered alloys is used to determine the anharmonic phonon entropy, and the chemical dependence to determine the phonon entropy of mixing. [Preview Abstract] |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P23.00003: Ambipolar diffusion and recombination of photoexcited carriers in bismuth films Yu-Miin Sheu, Yi-Jiunn Chien, Ctirad Uher, Stephen Fahy, David Reis Recent experimental and theoretical studies on bismuth show that intense ultrafast photoexcitation leads to a large- amplitude, softened coherent A1g phonon. Thus, the subsequent dynamics of the photoexcited carriers will strongly influence the dynamics of the phonon. However, little is known about the nonequilibrium carrier dynamics due to difficulty in separating carrier relaxation and other processes. Here we report ultrafast counter propagating optical pump-probe experiments, measuring photoexcited carrier transport across optically thick single crystal bismuth films at room temperature. The films are grown on transparent sapphire substrates with thicknesses varying between 185 and 385 nm, sufficient to separate the carrier dynamics from the effects of lattice heating and strain, when pumped and probed on opposite faces. The measured recombination time is about 14-30 ps and ambipolar diffusivity between 22 and 28 cm$^2$/s for the different films. The carrier recombination time is much longer than the A1g phonon period, supporting a two chemical potential model for the photoexcited electronic system and phonon dynamics, in which carrier diffusion (rather than electron-hole plasma cooling or recombination substantially reduces the carrier density over the lifetime of the phonon, leading to a chirped mode. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P23.00004: Magnetotransporet in ultra quantum Bismuth and related alloys Doron Bergman, Karyn Le Hur Recent studies of elemental Bismuth and related alloys in strong magnetic fields, have uncovered peculiar electric and thermal transport behavior (Behnia et al. Science 317, 1729 (2007), Banerjee PRB 78, 161103 (2008) ). In particular, the Hall resistivity resembles that of the fractional quantum Hall effect, in exhibiting quasi-plateaus, corresponding to fractional filling factors. At the same time anomolous features appear in the Nernst and Seebeck coefficients. Recent efforts to address possible interaction effects (Burnell et al., Alicea et al. preprints 2008), while suggesting interesting electronic states of Bismuth in this ultra quantum regime, have not explained the unusual transport phenomena. We investigate the transport phenomena in more detail, by using a microscropic model of the Bismuth band structure. We first explore Landau level physics in this model, and then go on to develop a theory of the anomoulous transport phenomena, using Boltzmann kinetic theory. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P23.00005: Angular dependent Nernst effect in Bi$_{x}$Sb$_{1-x }$ across the quantum limit Kamran Behnia, Zengwei Zhu, Benoit Fauqu\'e, Aritra Banerjee, Bertrand Lenoir The Fermi surface of bismuth occupies a tiny (10$^{-5})$ fraction of the Brillouin zone. Therefore, a field of 9 T oriented along the trigonal axis pushes the electrons to their lowest Landau level. Alloying bismuth with antimony reduces the carrier density and lowers this threshold field known as the quantum limit. Approaching this limit, the Nernst-Ettingshausen effect was found to display giant quantum oscillations whose magnitude is yet to be understood. The Nernst response presents sharp peaks each time a Landau level of hole-like quasi-particles meets the chemical potential. In addition to these peaks, a number of anomalies of unidentified origin were detected. Here, we present the first study of Nernst effect as a function of a rotating magnetic field in Bi$_{x}$Sb$_{1-x}$ up to 12 T. The results highlight the role played by the Dirac quasi-particles of the electron pockets in the generation of the unidentified anomalies. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P23.00006: Thermal transport properties of two-dimensional Dirac fermion Yousef Romiah, Xin-Zhong Yan, Chin-Sen Ting The self consistent Born approximation is utilized to obtain an expression for the electric and thermal currents needed for the calculation of thermal transport properties, including the Seebeck coefficient and the thermal conductivity. The validity of the Wiedemann-Franz law is checked. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P23.00007: Grain coarsening in crystals from evolution of dislocation densities : Results from a continuum theory of dislocation dynamics Woosong Choi, Yong Chen, Stefanos Papanikolaou, James Sethna, Surachate Limkumnerd Continuum theories of grain growth and coalescence dynamics currently use phase-field and other models without direct connection to the underlying dislocations which form the polycrystal grain boundaries. We extend a recently proposed wall-forming continuum dislocation dynamics theory\footnote{S. Limkumnerd and J. P. Sethna, Phys. Rev. Letters \textbf{96}, 095503 (2006)} to incorporate dislocation line tension energy, and explore the resulting coarsening dynamics in two dimensions. We report initial results both on scaling behavior, coarsening and coalescence mechanisms emerging from our theory, and compare to experimental results. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P23.00008: Smooth versus jerky motion of packets of dislocations across fields of obstacles. Catalin Picu, Renge Li We report on the transition from smooth (``unzipping'') to jerky motion of multiple interacting dislocations (elastic manifolds) moving across a field of randomly located obstacles under constant applied stress. The transition is controlled by the stress, the obstacle strength and distribution. The system exhibits spatial and temporal correlations (intermittency) similar to those observed experimentally at much larger scale in dislocation avalanches. Power law distributions of jump amplitudes and separation times emerge. Comparison of the simulation results with experimental data indicates that the jerky motion is more relevant for plastic deformation of real crystals than unzipping. The strain rate sensitivity parameter, $m$, decreases sharply when the system enters the jerky mode and becomes independent of the obstacle strength, presence of obstacles of various strengths and the way those are mixed, and of temperature. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P23.00009: Molecular-dynamics analysis of the mechanical behavior of face-centered cubic metallic ultrathin films Kedarnath Kolluri, M. Rauf Gungor, Dimitrios Maroudas We report results of large-scale molecular-dynamics simulations for the dynamic deformation under biaxial tensile strain of nanometer-scale-thick films of various face-centered cubic metals. Our results indicate that films of metals with moderate to high propensity for formation of stacking faults (e.g., Ni and Cu) exhibit an extended easy glide regime followed by a sharp increase in the material stress, whereas those with low propensity for stacking-fault formation (such as Al) exhibit a monotonic increase in the stress during dynamic loading. We find that the plastic strain rate in Cu and Ni thin films is far greater than that in Al thin films, leading to stress dissipation and an extended easy glide regime. Analysis of defect interaction mechanisms during dynamic deformation reveals dislocation annihilation, which is due to stacking-fault-mediated cross-slip mechanisms in Ni and Cu films and due to collinear interactions between dislocations in Al films. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P23.00010: Composition dependence of the elastic constants of $\beta $ and ($\alpha $~+~$\beta {\rm p}$-phase PdH$_{x}$ Douglas Safarik, Ricardo Schwarz, Stephen Paglieri, Dale Tuggle, Robert Quintana Previously [1], we measured the room-temperature elastic constants of
PdH$_{x}$ for 0~$<$~$x$~$<$~0.75. These measurements were done on single
crystals of $\alpha $-phase Pd(H) solid solution ($x$~$<$~0.01), of $\beta
$-phase Pd-H hydride ($x$~$>$~0.62), and of coherent two-phase mixtures of
$\alpha +\beta $ phases (0.01$ |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P23.00011: Adhesion Enhancement by Interfacial Microcrack Toughening Yue Qi, Haibo Guo, Xingcheng Xiao, Zhihui Xu, Xiaodong Li In this study, we reported a novel approach to enhance the adhesion of diamond coatings on titanium substrate by interfacial toughening. An array of oriented and confined micro-cracks around the interface was found to have the ability of opening and self-healing to release strain energy, by which to enhance macro-adhesion. Density functional theory calculations explained that cracks are energetically preferred to initiate and propagate along the (100) plane in titanium carbide interlayer. Thus by controlling the orientation of the interlayer for the failure associated with the delaminatation can be avoided for the coating/interlayer/substrate system. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P23.00012: Oxide-Dispersion Strengthened Nanoparticulate Composites with Application to Magnetic Materials Robert Cammarata, Stephen Farias, Chai-Ling Chien Metal matrix nanocomposites have been fabricated by a novel electrochemical deposition method in order to produce enhanced yield strength and creep resistant materials. Metals have been synthesized from an electrolytic solution containing a suspension of oxide nanoparticles. Using a rotating disk electrode, metal samples with a uniform dispersion of oxide nanoparticles are obtained. By controlling the concentration of particles in the solution, the electrode rotation rate, and deposition current density, the volume fraction of oxide in the nanocomposite can be sensitively controlled. Low load indentation testing reveals a substantial increase in room temperature yield strength compared to single phase metals that is close to that predicted from classical hardening models. Particular attention has given to magnetic materials such as Ni and FeCo with the aim of producing materials with improved mechanical behavior without significant degradation of the magnetic properties. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P23.00013: High pressure thermoelasticity of vanadium Daniel Orlikowski To support a larger effort for a multi-phase constitutive strength model for vanadium, we discuss the calculations performed to determine the anharmonic thermoelasticity for bcc and rhombohedral phases of vanadium. In this investigation, we have performed extensive calculations of the elastic moduli over broad ranges of temperature ($<$10,000 K) and pressure ($<$3 Mbar), accounting for both the electron-thermal and ion-thermal contributions. Using density functional theory (DFT) with the projector augmented-wave (PAW) methodology to calculate the electron-thermal component, we have combined this with the ion-thermal component, which is calculated from Monte Carlo (MC) canonical distribution averages of the strain derivatives on a multi-ion potential itself. The ion-potential is described through a many-body, quantum-based interatomic potential---the model generalized pseudopotential theory (MGPT). We suggest regions of stability for the rhombohedral structure in the phase diagram. The resulting elastic moduli are compared to available experimental results and to sound speeds measured along the Hugoniot. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P23.00014: Shock-wave dispersion and attenuation in discrete media, effect on source localization. Hasson Tavossi Shock wave speed and attenuation in a non-linear discrete media are investigated. The goal of the study is to identify parameters that control shock wave or impulsive wave speed and energy dissipation in the discrete non homogeneous binary media. Material properties of solid constituents and the elastic behavior of contact points are shown to depend on the wave frequency. The behavior at both high frequency and low frequency limits are analyzed. The effects of depth on wave velocity profile, wave spectral content and attenuation are also considered. Among applications are; accurate near ground shock wave source localization by microseism waves. [Preview Abstract] |
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