FY2010 - Oak Ridge National Laboratory

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Director’s R&D Fund— Neutron Sciences Results and Accomplishments The results of this project are grouped in terms of the manuscripts prepared during the subcontract period as follows. In Ref. 1 we report a novel Monte Carlo algorithm developed to accurately calculate the spinecho small-angle neutron scattering (SESANS) spectra. In Ref. 2 we report on a theoretical calculation to investigate the spectral features of SESANS for liquid particles under both repulsive and attractive intermolecular interactions. We found that the SESANS correlation function provides clear spectral features that elucidate the intermolecular correlation among interacting particles. In Ref. 3 we compare spectra between that of a liquid of uniform hard spheres and one of nonuniform hollow hard spheres. This work shows that due to the distinguishable length scales between intramoleuclar and intermolecular spatial correlations, it is possible to recognize the intramoleulcar scattering contribution to the SESANS as the density is varied. In Ref. 4 we explore the sensitivity of SESANS from a theoretical standpoint, and the results suggest there is a physical interpretation of the spatial variable in the SESANS correlation function. In Ref. 5 we investigate the effect of the interparticle potential with broken centrosymmetry on liquid structure and find that centrosymmetry particles and broken centrosymmetry particles exhibit different spectral features in the SESANS data over a wide range of dimension, consistent within their pair correlation functions. In Ref. 6 we find that it is conceptually important to fill in the “gap” in the theoretical calculation of γ(r) because these various theoretical approaches provide multiple tools for future research. And finally in Ref. 7 we will report on how our Monte Carlo algorithm can be extended to compute the SESANS correlation function of binary hard sphere particles of different diameters. Information Shared Li, X., C.‐Y. Shew, Y. Liu, R. Pynn, E. Liu, K. W. Herwig, J. L. Robinson, and W.‐R. Chen. 2010. “Theoretical studies on the structure of interacting colloidal suspensions by spin‐echo small angle neutron scattering.” J. Chem. Phys. 132, 174509 (2010). Shew, C.-Y, and W.-R. Chen. 2010. “A Monte Carlo algorithm for computing SESANS correlation functions in real space: Hard sphere liquids.” J. Chem. Phys. 132, 044906. (1) Shew, C.-Y., and W.-R. Chen. 2010. “A Monte Carlo algorithm for computing SESANS correlation functions in real space: Hard sphere liquids.” Journal of Chemical Physics 132, 044906. (2) Li, X., C.‐Y. Shew, Y. Liu, R. Pynn, E. Liu, K. W. Herwig, J. L. Robinson and W.‐R. Chen. 2010. “Theoretical studies on the structure of interacting colloidal suspensions by spin‐echo small angle neutron scattering.” J. Chem. Phys. 132, 174509. (3) Li, X., C.‐Y. Shew, Y. Liu, R. Pynn, E. Liu, K., W. Herwig, G. S. Smith, J. L. Robertson, and W.‐R. Chen. “Prospect of characterizing interacting soft colloidal structures using spin‐echo small angle neutron scattering,” J. Chem. Phys. (to be submitted). (4) Shew, C.‐Y., and W.‐R. Chen. “Structural sensitivity of SESANS for a high‐density hard sphere liquid”, J. Chem. Phys. (to be submitted). (5) Shew, C.‐Y., and W.‐R. Chen. “Simulation of liquid structure under the broken‐centrosymmetry potential” (in preparation). (6) Shew, C.‐Y., and W.‐R. Chen. “Revisit of theoretical calculation of Debye autocorrelation function” (in preparation). (7) Shew, C.‐Y., and W.‐R. Chen. “Simulation of SESANS correlation function for binary mixtures” (in preparation). 52
05306 Structure and Structure Evolution in Amorphous Materials— Fundamental Understanding of Materials Behaviors Far from Equilibrium X.-L. Wang, A. D. Stoica, K. C. Littrell, and J. R. Morris Director’s R&D Fund— Neutron Sciences Project Description The structure-property relationship is the cornerstone of materials science and engineering. Understanding a material’s structure and how it changes at different length scales is of paramount importance in materials design. Under extreme environments, materials are often thrown into a nonequilibrium state, whose behaviors cannot be understood with a simple extension of existing theories. Indeed, materials behavior far from equilibrium is one of the five scientific grand challenges identified by DOE. This project is intended to demonstrate ORNL’s ability to address fundamental questions in materials far from equilibrium using ORNL state-of-the-art characterization tools and computing facilities. The material of choice is metallic glass. Neutron scattering will be used as a primary tool to gain fundamental understanding of the structure of metallic glasses at multilength scales and, more importantly, how the structure features at different length scales evolve during phase transformation and mechanical deformation. The ability to conduct simultaneous measurements of diffraction and small-angle scattering in a complex sample environment represents a significant experimental challenge. Successful completion of this project will showcase the new instruments and scientific opportunities at the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR) and strengthen ORNL’s position in future funding calls. Mission Relevance Materials behavior far from equilibrium has been identified by the DOE Office of Basic Energy Sciences (DOEBES) as one of the five grand challenges that must be tackled “to address the DOE missions in energy efficiency, renewable energy resources, improved use of fissile fuels, safe and public acceptable nuclear energy, future energy sources, and reduced environmental impacts of energy production and use.” Unlike what happens under small perturbations, far-from-equilibrium behavior is not a simple extension of equilibrium state. Instead, it corresponds to qualitatively different types of behavior and response; in some cases, the materials have quite distinct properties (desirable or not) from their equilibrium behavior. To date, the microscopic origin of far-from-equilibrium behavior still remains a largely unchartered territory. In particular, experimental studies of far-from-equilibrium behavior have been plagued by the lack of research tools for in situ investigation of the dynamical process that characterizes the nonequilibrium transient behaviors. The advances in characterization tools such as the SNS are expected to break the in situ characterization barrier. By combining time-dependent diffraction and small-angle scattering, it will be possible to examine structural evolution simultaneously at different length scales, providing key information on the interaction of these scales. Results and Accomplishments We worked on two model systems, including zirconium- and calcium-based metallic glasses, to study their mechanical deformation and nanoscale crystallization behaviors. We have carried out in situ smallangle neutron scattering (SANS) experiments at HFIR and, as a demonstration, simultaneous diffraction and small-angle X-ray scattering (SAXS) experiments at the European Synchrotron Radiation Facility (ESRF), for a series of samples under tension and compression and/or also at elevated temperatures. Both SANS and SAXS data for calcium glasses indicated significant changes upon annealing, as indicated by visible interference peaks. 53
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FY2010 - Oak Ridge National Laboratory

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