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Hunter AH, Araullo-Peters V, Gibbons M, Restrepo OD, Niezgoda SR, Windl W, Flores KM, Hofmann DC, Marquis EA. Three-dimensional imaging of shear bands in bulk metallic glass composites. J Microsc 2016; 264:304-310. [PMID: 27513447 DOI: 10.1111/jmi.12443] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Revised: 05/17/2016] [Accepted: 06/08/2016] [Indexed: 11/30/2022]
Abstract
The mechanism of the increase in ductility in bulk metallic glass matrix composites over monolithic bulk metallic glasses is to date little understood, primarily because the interplay between dislocations in the crystalline phase and shear bands in the glass could neither be imaged nor modelled in a validated way. To overcome this roadblock, we show that shear bands can be imaged in three dimensions by atom probe tomography from density variations in the reconstructed atomic density, which density-functional theory suggests being a local-work function effect. Imaging of near-interface shear bands in Ti48 Zr20 V12 Cu5 Be15 bulk metallic glass matrix composite permits measurement of their composition, thickness, branching and interactions with the dendrite interface. These results confirm that shear bands here nucleate from stress concentrations in the glass due to intense, localized plastic deformation in the dendrites rather than intrinsic structural inhomogeneities.
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Affiliation(s)
- A H Hunter
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, U.S.A
| | - V Araullo-Peters
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, U.S.A
| | - M Gibbons
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, U.S.A
| | - O D Restrepo
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, U.S.A
| | - S R Niezgoda
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, U.S.A
| | - W Windl
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, U.S.A
| | - K M Flores
- Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University, St. Louis, Missouri, U.S.A
| | - D C Hofmann
- Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California, U.S.A
| | - E A Marquis
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, U.S.A
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Restrepo OD, Windl W. Full first-principles theory of spin relaxation in group-IV materials. Phys Rev Lett 2012; 109:166604. [PMID: 23215107 DOI: 10.1103/physrevlett.109.166604] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2010] [Revised: 05/24/2012] [Indexed: 06/01/2023]
Abstract
We present a generally applicable parameter-free first-principles method to determine electronic spin relaxation times and apply it to the technologically important group-IV materials silicon, diamond, and graphite. We concentrate on the Elliott-Yafet mechanism, where spin relaxation is induced by momentum scattering off phonons and impurities. In silicon, we find a ~T(-3) temperature dependence of the phonon-limited spin relaxation time T(1) and a value of 4.3 ns at room temperature, in agreement with experiments. For the phonon-dominated regime in diamond and graphite, we predict a stronger ~T(-5) and ~T(-4.5) dependence that limits T(1) (300 K) to 180 and 5.8 ns, respectively. A key aspect of this Letter is that the parameter-free nature of our approach provides a method to study the effect of any type of impurity or defect on spin transport. Furthermore we find that the spin-mix amplitude in silicon does not follow the E(g)(-2) band gap dependence usually assigned to III-V semiconductors but follows a much weaker and opposite E(g)(0.67) dependence. This dependence should be taken into account when constructing silicon spin transport models.
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Affiliation(s)
- O D Restrepo
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, USA
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Larson BC, Ku W, Tischler JZ, Lee CC, Restrepo OD, Eguiluz AG, Zschack P, Finkelstein KD. Nonresonant inelastic x-ray scattering and energy-resolved Wannier function investigation of d-d excitations in NiO and CoO. Phys Rev Lett 2007; 99:026401. [PMID: 17678238 DOI: 10.1103/physrevlett.99.026401] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2007] [Indexed: 05/16/2023]
Abstract
Nonresonant inelastic x-ray scattering measurements on NiO and CoO show that strong dipole-forbidden d-d excitations appear within the Mott gap at large wave vectors. These dominant excitations are highly anisotropic, and have [001] nodal directions for NiO. Theoretical analyses based on a novel, energy-resolved Wannier function (within the local density approximation+Hubbard U) show that the anisotropy reflects the local exciton wave functions and local point-group symmetry. The sensitivity to weak symmetry breaking in particle-hole wave functions suggests a wide application to strongly correlated systems.
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Affiliation(s)
- B C Larson
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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Cai YQ, Chow PC, Restrepo OD, Takano Y, Togano K, Kito H, Ishii H, Chen CC, Liang KS, Chen CT, Tsuda S, Shin S, Kao CC, Ku W, Eguiluz AG. Low-energy charge-density excitations in MgB2: Striking interplay between single-particle and collective behavior for large momenta. Phys Rev Lett 2006; 97:176402. [PMID: 17155487 DOI: 10.1103/physrevlett.97.176402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2006] [Indexed: 05/12/2023]
Abstract
A sharp feature in the charge-density excitation spectra of single-crystal MgB2, displaying a remarkable cosinelike, periodic energy dispersion with momentum transfer (q) along the c* axis, has been observed for the first time by high-resolution nonresonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-q collective mode residing in the single-particle excitation gap of the B pi bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB2.
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Affiliation(s)
- Y Q Cai
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
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