Ultrasonics studies of point defects in iron, aluminum-lithium, and gallium arsenide
Igarashi, Brian
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https://hdl.handle.net/2142/23852
Description
Title
Ultrasonics studies of point defects in iron, aluminum-lithium, and gallium arsenide
Author(s)
Igarashi, Brian
Issue Date
1995
Doctoral Committee Chair(s)
Granato, A.V.
Department of Study
Physics, Condensed Matter
Discipline
Physics, Condensed Matter
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
The ultrasonics studies undertaken in this work illustrate the applicability of ultrasonics to a broad variety of problems. In the case of Fe, the objective is to measure the production and annealing of the diaelastic effect of self-interstitials in Fe. Frenkel Pairs created by 2.3 MeV electron bombardment cause the shear moduli, $\rm C\sp\prime\ and\ C\sb{44},$ to soften by ($\rm-27\pm2)\%\ and\ (-17\pm4)\%,$ per at.% pair. The magnitudes are of the same order as for Cu, but the observed anisotropy matches that detected in Mo, the only other bcc metal tested.
Measurements in an AlLi alloy provide an opportunity to test the first predictions of configurations of point defects derived from first-principles calculations. An Al self-interstitial trapped by a Li atom is predicted to form a complex with trigonal symmetry; however, ultrasonic measurements of an AlLi alloy irradiated by 2.3 MeV electrons give strong evidence that the complex is a mixed dumbbell with tetragonal symmetry. A C$\sp\prime$ relaxation peak occurs at $\sim$20.5 K, but no C$\sb{44}$ relaxation is observed between 2 K and 180 K. Subsequent experiments with Fe added to the alloy demonstrate that the mixed dumbbell migrates as an intact unit between 80 K and 130 K, and it dissociates at 200 K.
Cr$\sp{3+}$ in GaAs has been shown by several thermal conductivity and electron paramagnetic resonance studies to yield a $$-orthorhombic Jahn-Teller distortion, but ultrasonic data about this defect is limited. Present ultrasonic measurements of an illuminated sample show that Cr$\sp{3+}$ gives both C$\sp\prime$ and C$\sb{44}$ relaxations. A tunneling model of Cr$\sp{3+}$ is developed to account for the 1/T-dependencies of the direct process relaxation rate and relaxation modulus softenings. The model also yields estimates of the Jahn-Teller coefficients of Cr$\rm\sp{3+},\ \vert V\sb{E}\vert = 4.6\ eV/\A\ and\ \vert V\sb{T}\vert = 1.6\ eV/\A.$
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