Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 6 of 6
Full-Text Articles in Physics
Photorefraction In Batio3, Stephen Ducharme
Photorefraction In Batio3, Stephen Ducharme
Stephen Ducharme Publications
This thesis summarizes the results of experimental investigations of the photorefractive properties of melt-grown BaTiO3 single crystals. Three basic photorefractive material properties are studied: (1) the effective density of photorefractive charges, (2) the photoconductivity of the photorefractive charges, and (3) the relative contributions of electron and hole photoconduction. Volume holographic measurement techniques are used: two-beam energy coupling, four-wave mixing, and erasure of volume holograms. The photorefractive properties were altered experimentally by chemically reducing or oxidizing a BaTiO3 crystal. I have extended the “hopping conduction” model of photorefractive transport to include simultaneous electron and hole photoconduction. The extension of …
Ferromagnetism Versus Antiferromagnetism In Face-Centered-Cubic Iron, F. J. Pinski, J. Staunton, B. L. Gyorffy, Duane D. Johnson, G. M. Stocks
Ferromagnetism Versus Antiferromagnetism In Face-Centered-Cubic Iron, F. J. Pinski, J. Staunton, B. L. Gyorffy, Duane D. Johnson, G. M. Stocks
Duane D. Johnson
Using a first-principles disordered-local-moment picture of itinerant-electron magnetism, we calculated the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state.
Density-Functional Theory For Random Alloys: Total Energy Within The Coherent-Potential Approximation, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Gyorffy, G. M. Stocks
Density-Functional Theory For Random Alloys: Total Energy Within The Coherent-Potential Approximation, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Gyorffy, G. M. Stocks
Duane D. Johnson
A density-functional-based theory is developed for calculation of the total energy and pressure of random substitutional alloys within the Korringa-Kohn-Rostoker coherent-potential approximation. The theory is used to calculate the concentration variation of the equilibrium lattice spacing of α-phase CucZn1−c alloys. We find, in agreement with experiment, that the variation is almost linear and that it deviates from Vegard's rule.
Effect Of Strain On Muon Diffusion And Trapping In Metal By Bassam Salim Hitti, Bassam Salim Hitti
Effect Of Strain On Muon Diffusion And Trapping In Metal By Bassam Salim Hitti, Bassam Salim Hitti
Dissertations, Theses, and Masters Projects
Positive muons implanted in metal distort the surrounding lattice; therefore, in addition to electronic interactions, the elastic forces have to be considered in determining the muon state. to explore the elastic and electronic diffusion and trapping mechanisms, we studied AlCu(,420ppm), AlMg(,1000ppm) and AlAg(,1000ppm) alloys. These alloys were selected for the different effects on the host lattice of these impurities; Cu contracts the Al lattice, Mg expands it and Ag has nearly no effect. On the other hand Cu and Ag are monovalent while Mg is divalent. For AlCu between 5K and 14K the temperature exponent (beta) of the two-state-model trapping …
Determination Of The Vacancy Migration Energy Of Aluminum By Nmr, Terry William Gullion
Determination Of The Vacancy Migration Energy Of Aluminum By Nmr, Terry William Gullion
Dissertations, Theses, and Masters Projects
Monovacancy diffusion is a thermally activated process characterized by an activation energy E(,d). The diffusion of atoms requires the formation and migration of vacancies. The concentration of vacancies n/N is given by n/N (DBLTURN) exp(-E(,f)/kT). It can be shown that the activation energy E(,d) is the sum of the energy to form a vacancy E(,f) and the energy required for an atomic jump E(,m): E(,d) = E(,f) + E(,m). Furthermore, the atomic jump rate (omega)(,j) can be shown to be thermally activated and given by (omega)(,j) (DBLTURN) (nu)(,o)(n/N)exp(-E(,m)/kT) ((nu)(,o) is the attempt frequency).;NMR offers many techniques to measure the activation …
A Nuclear Magnetic Resonance Study Of Deuterated Poly(Vinylidene Fluoride) And A Copolymer Of Deuterated Vinylidene Fluoride And Tetrafluoroethylene, Montee A. Doverspike
A Nuclear Magnetic Resonance Study Of Deuterated Poly(Vinylidene Fluoride) And A Copolymer Of Deuterated Vinylidene Fluoride And Tetrafluoroethylene, Montee A. Doverspike
Dissertations, Theses, and Masters Projects
Pulsed deuterium NMR experiments have been performed on deuterated samples of poly(vinylidene fluoride), PVF(,2), repeat unit CH(,2)CF(,2) and the copolymer poly(vinylidene fluoride)-tetrafluoroethylene (80-20), (PVF(,2)-F(,4)E). A deuterium line shape study has been employed to characterize the orientational distribution of the dipole moments in both poled and unpoled samples. In addition, the orientational distributions of chain axis alignment has been measured in stretched samples.;PVF(,2) and PVF(,2)-F(,4)E exhibit unique piezoelectric and pyroelectric properties which are due to their crystalline components (approximately 50% in typical material). Four crystalline phases exist in the homopolymer PVF(,2), the (alpha), (beta), (gamma), and the (delta). The relatively electrically …