Disorder-driven nonequilibrium melting studied by electron diffraction, brillouis scattering, and molecular dynamics

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In the present paper, a brief overview of the electron diffraction, Brillouin scattering and molecular dynamics studies of radiation-induced amorphization of ordered intermetallic compounds is presented. In these studies, measured changes in the velocity of surface acoustic phonons, lattice constant, and the Bragg-Williams long-range order parameter induced by irradiation were compared with the results of computer simulations of defect-induced amorphization. The results indicate that progressive chemical disordering of the superlattice structure during irradiation is accompanied by an expansion of the lattice and a large change in sound velocity corresponding to a {approximately} 50% decrease in the average shear modulus. The ... continued below

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24 p.

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Okamoto, P. R.; Lam, N. Q. & Grimsditch, M. December 21, 1999.

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In the present paper, a brief overview of the electron diffraction, Brillouin scattering and molecular dynamics studies of radiation-induced amorphization of ordered intermetallic compounds is presented. In these studies, measured changes in the velocity of surface acoustic phonons, lattice constant, and the Bragg-Williams long-range order parameter induced by irradiation were compared with the results of computer simulations of defect-induced amorphization. The results indicate that progressive chemical disordering of the superlattice structure during irradiation is accompanied by an expansion of the lattice and a large change in sound velocity corresponding to a {approximately} 50% decrease in the average shear modulus. The onset of amorphization occurs when the average shear modulus of the crystalline compound becomes equal to that of the amorphous phase. This elastic softening criterion for the onset of amorphization and the dependence of the average shear modulus on the long-range-order parameter are in excellent agreement with molecular dynamics simulations. Both the experimental observations and computer simulations confirm the predictions of the generalized Lindemann melting criterion which stipulates that thermodynamic melting of a defective crystal occurs when the sum of the dynamic and static mean-square atomic displacements reaches a critical value identical to that for melting of the defect-free crystal. In this broader view of melting, the crystal-to-glass transformation is a disorder-driven nonequilibrium melting process occurring at temperatures below the Kauzmann isentropic glass-transition temperature.

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24 p.

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INIS; OSTI as DE00751864

Medium: P; Size: 24 pages

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  • Advanced Studies Institute (ASI-002) Exploration of Subsurface Phenomena by Particle Scattering Naval Postgraduate School, Monterey, CA (US), 10/19/1998--10/23/1998

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  • Report No.: ANL/MSD/CP-100784
  • Grant Number: W-31109-ENG-38
  • Office of Scientific & Technical Information Report Number: 751864
  • Archival Resource Key: ark:/67531/metadc712173

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  • December 21, 1999

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  • Sept. 12, 2015, 6:31 a.m.

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  • April 10, 2017, 4:41 p.m.

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Okamoto, P. R.; Lam, N. Q. & Grimsditch, M. Disorder-driven nonequilibrium melting studied by electron diffraction, brillouis scattering, and molecular dynamics, article, December 21, 1999; Illinois. (digital.library.unt.edu/ark:/67531/metadc712173/: accessed July 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.