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Title:Thermal conductivity and electrical resistivity of cemented carbides, titanium diboride and high temperature ceramic superconductors
Author(s):Frandsen, Marvin Vaun
Doctoral Committee Chair(s):Williams, W.S.
Department / Program:Physics
Subject(s):thermal conductivity
electrical resistivity
cemented carbides
titanium diboride
high temperature ceramic superconductors
phono electron interaction
cemented transition-metal carbides
Abstract:This project studied the interaction between phonons and electrons, and between these entities and defects in high temperature ceramic superconductors, cemented transition-metal carbides and Ti~~. These interactions were studied via measurement and analysis of thermal conductivity and electrical resistivity from 15-1400 oK. It has been reported that YB8:2CU:-sO-7--,.. exhibits a significant rise in thermal conductivity just below the superconducting transition temperature, Te. This rise, or phonon bump, has been attributed to decreased scattering of phonons by electrons. The phonon bump in a high temperature superconductor is here quantitatively analyzed for the first time. The effect is attributable to a factor of two decrease in phonon-electron scattering below as compared to above Teo. Thus phonon-electron scattering in YB&:!CU:~O-7--.. appears to play a part in lattice thermal resistance even in the superconducting state. The small phonon bump in YB8..;;~CU;:!l'O-7"-.. is to be contrasted with the dramatic rise in lattice thermal conductivity of superconducting NbC~, which increases two orders of magnitude as NbC•. passes through T~;: . iv Electrical resistivity measurements of the Bi-Sr-Ca-Cu-O superconducting system with different compositions show interesting behaviors. Two compositions exhibit resistivity saturation below room temperature. All compositions contain a phase which demonstrates a superconducting phase transition at 85 oK; one composition manifests a superconducting phase transition at 115-120 oK. In cemented carbides it is found that phonon and electron scattering from defects is the dominant cause of variations in thermal and electrical conductivity above 80 oK. Cemented carbides made primarily of nonstoichiometric cubic carbides possess a dramatically lower thermal conductivity than WC-based cemented carbides. An increase in amount of binder phase lowers the thermal conductivity of a cemented carbide. This effect is ascribed to phonon and electron scattering from dissolved Wand C atoms in the binder phase. An increase in carbide grain size increases the thermal conductivity of a cemented carbide. This effect is attributed to an increase in carbide grain contiguity and the dominant role of the carbide phase in thermal conduction in WC-based cemented carbides. This conclusion is strengthened by the observation of a large decrease in thermal conductivity with the addition of a third phase of a solid solution of nonstoichiometric cubic carbide grains. In high purity polycrystalline titanium diboride it is found that scattering of phonons and electrons from defects is an important cause of thermal resistivity. The scattering centers are boron vacancies and particles of elemental carbon.
Issue Date:1988
Genre:Dissertation / Thesis
Rights Information:1988 Marvin Vaun Frandsen
Date Available in IDEALS:2011-05-17
Identifier in Online Catalog:1855429

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