Low temperature anomalies in niobium, vanadium and tantalum
Sellers, Gregory Jude
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https://hdl.handle.net/2142/30671
Description
Title
Low temperature anomalies in niobium, vanadium and tantalum
Author(s)
Sellers, Gregory Jude
Issue Date
1975
Director of Research (if dissertation) or Advisor (if thesis)
Anderson, A.C.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
niobium
vanadium
tantalum
low temperature anomally
Language
en
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.
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