Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W15: Glasses and Quasicrystals |
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Sponsoring Units: DCMP Chair: Erdal C. Oguz, Princeton University Room: 008B |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W15.00001: Correlation of Local Structure and Electronic Properties of Glass Materials Vincenzo Lordi, Nicole Adelstein Wide band gap glasses such as silica and its derivatives are typically considered insulators. However, electronic transport in glasses can be important for certain applications, such as when used as the host material for a scintillator radiation detector. Here we explore the relationship between local structure in glass materials and the corresponding electronic properties of carrier transport and charge trapping. We present a novel analysis that decomposes the distribution of localized band tail states in terms of specific local structural features in the glass. Comparison of the structure-related transport properties of different glass compositions is given, using silica and sodium silicate as prototypes. [Preview Abstract] |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W15.00002: Structural manifestations of aging in Se-rich glasses S. Dash, S. Ravindren, P. Chen, P. Boolchand We examine weakly cross-linked GexSe100-x (0{\%}\textless x\textless 7{\%}) binary glasses in modulated DSC and Raman scattering experiments. Homogeneity of melts was carefully verified using FT-Raman line profiling. Upon aging at RT for 4 months, we find the width of the glass transition W(x) steadily decreasing from 10C at 7{\%} Ge to 2C for pure Se. The 5-fold reduction of W(x) with a decrease of Ge content is accompanied by a 2-fold increase in the non-reversing enthalpy. Rejuvenation of the aged glasses changes W(x) from 15C at 7{\%} Ge to 7C for pure Se. Tg is found to decrease upon rejuvenation with the difference (Tg(aged)--Tg(rejuv)) showing a maximum near 3{\%} Ge and vanishing for pure Se and 6{\%} of Ge, which are topological thresholds. These results in Se-rich glasses are consistent with aging induced decoupling of Se8 crowns and growth of extended range structural correlations between polymeric Sen chains due to lone pair interactions. At higher x, near 8-10{\%} of Ge, eutectic effects are manifested. [Preview Abstract] |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W15.00003: The effect of semiconducting CdSe and ZnSe nanoparticles on the fluorescence of Sm$^{3+}$ in lead borate glasses Saisudha Mallur, Stephen Fatokun, P.K. Babu We studied the fluorescence spectra of Sm$^{3+}$ doped lead borate glasses containing zinc selenide (ZnSe) and cadmium selenide (CdSe) nanoparticles with the following compositions (x PbO: 96.5-x B$_{2}$O$_{3}$:0.5 Sm$_{2}$O$_{3}$:3ZnSe/CdSe, x$=$36.5 and 56.5 mol{\%}). These glass samples are prepared using the melt-quenching technique. Each sample is annealed just below the glass transition temperature at 400$^{\circ}$C for 3 hrs and 6 hrs. We have chosen PbO-B$_{2}$O$_{3}$ glasses to incorporate Sm$^{3+}$ ions because they have large glass forming region, high refractive index, and good physical and thermal stability. Fluorescence spectra of these samples are obtained with the excitation wavelength at 477 nm. Four fluorescence transitions are observed at 563 nm, 598 nm, 646 nm and 708 nm. The transition at 646 nm is found to be a hypersensitive transition that strongly depends on the covalency of the Sm-O bond and the asymmetry of the crystal field at Sm site. The 646 nm/598 nm fluorescence intensity ratio has been studied for different annealing times and PbO concentration for both ZnSe and CdSe samples. The presence of CdSe nanoparticles is seen to produce the greatest influence on the fluorescence intensity ratio. This could be due to the size of the CdSe nanoparticles and covalency of the Sm-O bond. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W15.00004: Topological phases in Ba-Borate glasses Chad Holbrook, Andrew Czaja, Punit Boolchand Twelve compositions in the (BaO)$_{x}$(B$_{2}$O$_{3})_{100-x}$ pseudo binary, in the 15{\%} \textless x \textless 40{\%} range, were synthesized by induction melting Boric acid and anhydrous BaCO$_{3}$, taking care to handle the materials in a dry ambient environment. Modulated- DSC and Raman scattering experiments were undertaken systematically as function of BaO content (x). Calorimetric measurements reveal T$_{g}$(x) to show a broad maximum and the non-reversing enthalpy to show a Gaussian-like reversibility window$^{2}$, both centered near x $=$ 28{\%}. Raman scattering displays rich lineshapes with modes similar to those observed in Na-Borates$^{2}$. Modes near 808 cm$^{-1}$, 770 cm$^{-1}$, 740 cm$^{-1}$ and 705 cm$^{-1}$ are observed, and identified with breathing modes of pure and mixed rings from characteristic structural groupings$^{2}$. These preliminary results suggest that glasses at x \textless 24{\%} are in the stressed-rigid phase, in the 24{\%} \textless x \textless 30{\%} in the Intermediate Phase and at x \textgreater 30{\%} in the flexible phase. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W15.00005: Revealing Structural Details of SiCO Ceramics with GIPAW Calculations of Model Structures and Analysis of Experimental $^{29}$Si Nuclear Magnetic Resonance Spectroscopy John Nimmo, Peter Kroll The occurrence of the various SiCxO4-x (1$\le $x$\le $4) mixed tetrahedra in silicon oxycarbide (SiCO) is often quantified by means of experimental 29Si nuclear magnetic resonance. The structural centers are assigned to individual peaks in the spectrum, which can be integrated to give the relative populations. Using a recently-developed method, we show that is is also possible to recover information on the connectivity of these tetrahedra. By combining a huge library of model structures an GIPAW calculations, we show that simple relations exist between the Si-O-Si linking angles and the 29Si NMR chemical shift. In this work, we perform detailed analyses of SiCO 29Si NMR spectra available in literature. We extract angular distributions in agreement with the experimental X-ray and neutron diffraction data. Furthermore, in glasses with large amounts of so-called ``free'' carbon, we observe a significant portion of the \textbraceleft Si\textbraceright O4 tetrahedra which have disproportionately large angles. These angles indicate the presence of internal SiO2 surfaces or cages-like voids, similar to those found in zeolites or clathrates. This analysis suggests that in SiCO, the ``free'' carbon is incorporated into these voids, which produces strain on the bonding angles of the surrounding host glass. [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W15.00006: Correlations between dynamics and atomic structures in Cu$_{64.5}$Zr$_{35.5}$ metallic glass C.Z. Wang, Y. Zhang, F. Zhang, M.I. Mendelev, M.J. Kramer, K.M. Ho The atomic structure of Cu-Zr metallic glasses (MGs) has been widely accepted to be heterogeneous and dominated by icosahedral short range order (ISRO). However, the correlations between dynamics and atomic structures in Cu-Zr MGs remain an enigma. Using molecular dynamics (MD) simulations, we investigated the correlations between dynamics and atomic structures in Cu$_{64.5}$Zr$_{35.5}$ MG. The atomic structures are characterized using ISRO and the Bergman-type medium range order (BMRO). The simulation and analysis results show that the majority of the mobile atoms are not involved in ISRO or BMRO, indicating that the dynamical heterogeneity has a strong correlation to structural heterogeneity. Moreover, we found that the localized soft vibration modes below 1.0 THz are mostly concentrated on the mobile atoms. The diffusion was studied using the atomic trajectory collected in an extended time interval of 1.2 $\mu$s at 700 K in MD simulations. It was found that the long range diffusion in MGs is highly heterogeneous, which is confined to the liquid-like regions and strongly avoids the ISRO and the Bergman-type MRO. All These results clearly demonstrate strong correlations between dynamics (in terms of dynamical heterogeneity and diffusion) and atomic structures in Cu$_{64.5}$Zr$_{35.5}$ MGs. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W15.00007: Onset of plasticity and its relation to structure in CuZr metallic glasses: a molecular dynamics study Gonzalo Gutierrez, Matias Sepulveda, Nicolas Amigo The plastic behavior of crystalline metals is well understood. It is known that this regime is mainly mediated by the nucleation and propagation of dislocations as well as by grain boundary sliding. In metallic glasses (MGs), the plastic behavior is quite different from their crystalline counterparts. It is well known that bulk metallic glasses, in addition to the high yield strength and a elastic deformation to a strain limit about 2 \% (i.e., more than an order of magnitude greater than conventional crystalline metals), are brittle at room temperature. Interestingly, MG nanowires present an important degree of ductillity, and is an ideal system to study the onset of plasticity in MG. Here we present a computational tensile test which shows the evolution of the atomic structure of a Cu$_{50}$Zr$_{50}$ metallic glass nanowire at 300 K according to the applied strain increased. The system consists of a million atoms CuZr nanowire metallic glass. Local structure of atoms is analyzed by means of the Voronoi polyhedral technique and the nucleation and propagation of SBs by monitoring the atomic strain. [Preview Abstract] |
Thursday, March 5, 2015 3:54PM - 4:06PM |
W15.00008: Study the formation of metastable crystalline phases from amorphous metallic systems with an integrated approach Zhuo Ye, Feng Zhang, Yang Sun, Mikhail Mendelev, Ryan Ott, Eun-soo Park, Matt Besser, Matt Kramer, Cai-Zhuang Wang, Kai-Ming Ho An efficient genetic algorithm (GA) is integrated with experimental diffraction data to solve a metastable Al$_{\mathrm{20}}$Sm$_{\mathrm{4}}$ phase that evolves during rapid solidification of an amorphous Al-10{\%}Sm alloy produced by magnetron sputtering. The excellent match between calculated and experimental X-ray diffraction patterns confirms that this new phase appeared in the crystallization of the alloy. We discover the strong similarity of the underlying atomic structure between the amorphous alloy and this phase. Both phases share the same Sm-centered motif, providing a low-barrier pathway to form this Al$_{\mathrm{20}}$Sm$_{\mathrm{4\thinspace }}$phase in the glass matrix at low temperatures. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered anti-site defects in the devitrified crystal. [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W15.00009: Ab Initio Simulation of Nickel-Palladium-Phosphorus Bulk Metallic Glasses Raymond Atta-Fynn, Parthapratim Biswas Using first principles molecular dynamics simulations, we model the structural and electronic properties of Ni$_{40}$Pd$_{40}$P$_{20}$~bulk metallic glasses. The calculations are carried out for large system sizes in order to probe structural features associated with the medium range order on the nanometer length scale. We discuss different approaches to modeling the glassy systems ranging from the cook-and-quench to the structural building block techniques. The nature of the medium range order on the nanometer length scale is examined using the theory of fluctuation electron microscopy.~ The localization nature of the electronic eigenstates and the dc conductivity (of the model configurations) will be discussed in relation to the real space atomic structure. [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W15.00010: Microscopic pathway of a polymorphic transformation in Al90Sm10 system by molecular dynamics simulations Yang Sun, Feng Zhang, Zhuo Ye, Mikhail Mendelev, Ryan Ott, Matthew Kramer, Cai-Zhuang Wang, Kai-Ming Ho When as-quenched amorphous Al-10.at{\%}Sm alloy is isochronally heated up, it can display a nearly perfect polymorphic transformation into a complex cubic phase. Knowledge about the pathway of this transformation plays a key role for understanding the phase selection in this system driven far from equilibrium. We successfully simulated the growth of this crystalline phase from the amorphous state using molecular dynamics, with the help of a preexisting crystalline seed. The as-grown structure is in good agreement with experimental X-ray diffraction measurement. By analyzing the atomic trajectories during growth, we show the microscopic pathway linking the amorphous and crystalline phases and how the transformation is controlled by the driving force, atomic diffusivities and structural topologies. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W15.00011: Quasilattice-conserved molecular dynamics study of the atomic structure of decagonal Al-Co-Ni quasicrystals Yu-Jun Zhao, Xiaotian Li The detailed atomic structure of quasicrystals has been an open question for decades. In this paper, we present a quasilattice-conserved molecular dynamics method (quasiMD), with particular quasiperiodic boundary conditions. As the atomic coordinates are described by basic cells and quasilattices, we are able to maintain the self-similarity characteristics of qusicrystals with the atomic structure of the boundary region updated timely following the relaxing region. Exemplified with the study of decagonal Al-Co-Ni (d-Al-Co-Ni), we propose a more stable atomic structure model based on Penrose quasilattice and our quasiMD simulations. In particular, ``rectangle-triangle'' rules are suggested for the local atomic structures of d-Al-Co-Ni quasicrystals. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W15.00012: Local density fluctuations and hyperuniformity in quasicrystals Erdal Celal O\u{g}uz, Salvatore Torquato Local density fluctuations in many-body systems are of fundamental importance throughout various scientific disciplines, including physics, materials science, number theory and biology. In a point pattern, let the variance associated with the number of points contained in a spherical window of radius $R$ be denoted by $\sigma^2(R)$. Hyperuniform point patterns in $d$ dimensions do not possess infinite-wavelength fluctuations or, equivalently, possess a number variance that grows more slowly than the window volume, i.e., $R^d$ [1]. Hyperuniform systems include all infinite periodic structures, aperiodic quasicrystals, and some special disordered systems. Previous investigations showed that the number variance for large $R$ in hyperuniform systems serves as a useful metric to rank order systems according to the degree to which large-scale density fluctuations are suppressed. In this work, we investigate the number variance of two-dimensional quasicrystals with a variety of different rotational symmetries. We study how the number variance depends on the rotational symmetry and local isomorphism class of the quasicrystal. We compare these results to a number of different periodic systems as well as disordered hyperuniform systems. \\[4pt] [1] S. Torquato, F. H. Stillinger, PR E, 68 (2003) [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W15.00013: Growth of icosahedral quasicrystals Joshua Socolar, Connor Hann, Paul Steinhardt The discovery of an icosahedral quasicrystal that formed naturally in a rock sample originating from a meteorite highlights fundamental questions about quasicrystal formation.\footnote{Bindi, Steinhardt, Yao, and Lu. {\it Science}, {\bf 324}:1306 (2009).} ?The growth of a well-ordered quasicrystal through kinetics dominated by local energetics is known to be possible in principle for 2D systems: a Penrose tiling, for example, can be grown from a particular type of small seed by adding tiles only to surface sites where the tile type and orientation are unambiguously determined by already placed tiles that share a vertex.\footnote{Onoda, Steinhardt, DiVincenzo, and Socolar, {\it PRE} {\bf 60}:2653 (1988).} We consider the generalization of this result to icosahedral quasicrystal tilings comprised of Ammann rhombohedra. Numerical simulations strongly suggest that infinite, well-ordered, icosahedral quasicrystals can be generated. Unlike the 2D case, defects are generated outside the original seed, but the number of such defects appears to grow only linearly with the cluster radius. Analysis of the lift of the tiling to a 6D hypercubic lattice provides key insights into the growth mechanism. [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W15.00014: The Log-Lin Metric for Generic Responses in Logarithmic Structures Antony J. Bourdillon The generic Log-Lin metric joins experimental quasicrystal data with its ideal structure. How does a periodic probe, $e.g. $an X-ray or electron beam, interact with an `aperiodic' solid to produce sharp diffraction in geometric space? Based on the structure [1-2], and through its stretching factor in the hierarchic model, quasi-structure factors are expanded in geometric series. The Log-Lin metric is found to be a function of tau$^{2}$ and pi [3-4]. The solution is of special value in simulating not only icosahedral structures, but also defective logarithmic solids, and quasicrystals of lower symmetry. The metric, now analyzed and simulated, enables consistent measurement from the atomic scale to high order superclusters. It is essential in any wave interaction with logarithmic solids. The factor applies to physical clusters of extremely dense, binary, hard-sphere, icosahedral, unit cells.\\[4pt] [1] Bourdillon, A.J., \textit{Micron, }\textbf{51} 21-25 (2013): doi: 10.1016/j.micron.2013.06.004.\\[0pt] [2] Bourdillon, A.J. APS March Meeting, Baltimore, March 18-22 (2013) session W43.\\[0pt] [3] Bourdillon, A.J.,\textit{ J. Mod. Phys. }\textbf{5} 1079-1084 (2014): doi.org/10.4236/jmp.2014.512109.\\[0pt] [4] APS Far West Section Meeting, Reno, October 24-25 (2014) [Preview Abstract] |
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