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1975 SellersPDF


Title:Low temperature anomalies in niobium, vanadium and tantalum
Author(s):Sellers, Gregory Jude
Director of Research:Anderson, A.C.
Department / Program:Physics
low temperature anomally
Abstract:The specific heats of superconducting Nb, V and Ta and of normal Ta have been measured in the temperature range 0.05 - 2 K in an outgassed condition and with H or D added as interstitial solutes. The presence of H or D in these bcc transition metals produces an isotope dependent specific heat anomaly which can dominate the normal lattice contribution and which appears to be related to a disp1acive motion of the interstitial H or D. No evidence is found in these metals which would be suggestive of a second superconducting energy gap. The thermal conductivities of superconducting Nb and Ta samples have also been measured in the temperature range 0.04 - 4 K, both outgassed and with dissolved H or D. The presence of H or D results in a decrease of the thermal conductivity. In Nb doped with D the phonon mean free path exhibits a minimum which occurs at the same temperature at which a deuterium related anomaly has been observed in the specific heat. Phonon scattering caused by the addition of H to Nb or Ta is complicated by the presence of resonant scattering from dislocations produced by precipitation of the ~-phase hydride. A technique has been developed which permits the accurate measurement of heat capacities to very low temperatures without the use of a heat-switch. As a test of this technique the specific heat of Cu, with and without hydrogen impurities, has been measured in the temperature range 0.04 - 1 K. The presence of hydrogen increases the specific heat by ~% as has been reported previously at higher temperatures. Above 0.3 K the data for hydrogen-free copper are in good agreement with the copper reference equation. At lower temperatures there is an additional contribution to the heat capacity which might be associated with oxygen impurities.
Issue Date:1975
Genre:Dissertation / Thesis
Rights Information:Copyright 1975 Gregory Jude Sellers
Date Available in IDEALS:2012-04-19

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