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|Title:||Influence of Structural Relaxation Upon the Low Temperature Properties of Metallic Glasses|
|Author(s):||Cotts, Eric John|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||We have investigated the low temperature properties of metallic glasses. We find that below 1K, the thermal conductivity of metallic glasses (Fe(,40)Ni(,40)P(,14)B(,6), Pd(,77.5)Si(,16.5)Cu(,6) and Zr(,3)Rh) is similar to that of the large class of amorphous materials previously investigated, including other metallic glasses. We have analyzed the influence of the electron-phonon interaction upon the phonon thermal conductivity (kappa)(,ph) (T < 1K) in PdSiCu. Our quantitative results agree well with theoretical prediction. We have found no effect upon (kappa)(,ph) due to boundary scattering in our samples. We have deduced the "glassy" thermal conductivity (kappa)(,glass) for Zr(,3)Rh and PdSiCu from our measurements, where 1/(kappa)(,glass) is the thermal resistivity intrinsic to the disordered state of the solid.
The focus of this investigation has been upon the influence of structural relaxation upon the low temperature properties of metallic glasses. For the first time, the thermal conductivity (kappa)(,glass) of glassy metals was shown to change reversibly with heat treatment at temperature T(,A) near the glass transition. The change of (kappa)(,glass) is interpreted as resulting from a change in the density N(E) of the two-level-states (TLS) found in amorphous solids. A linear dependence of N(E) upon T(,A) is consistent with our observations.
We have compared our results with a model of the glass transition and structural relaxation based upon a free-volume approach, developed by Cohen, Turnbull and Grest (CTG). The CTG model suggests that the TLS should be assigned to the tunneling of atoms adjacent to voids. The number of voids (or TLS, N(E)) is related by CTG directly to the free volume. A quantitative relation between free volume and the metastable equilibrium temperature of the glass is suggested by the CTG model. We associate the metastable equilibrium temperature with our anneal temperature T(,A); in this context the CTG model predicts N(E) (PROPORTIONAL) T(,A). This prediction is consistent with our observations of a reversible change of N(E) in metallic glasses upon anneal. Our ability to reversibly manipulate the structure and density of two-level-states of metallic glasses provides support for the free volume model, and thus suggests a description of the structural origin of the two-level-states.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.
|Date Available in IDEALS:||2015-05-13|