An ultrasonic study of trapped hydrogen tunneling systems in Nb and Ta
Maschhoff, Kevin Robert
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https://hdl.handle.net/2142/25230
Description
Title
An ultrasonic study of trapped hydrogen tunneling systems in Nb and Ta
Author(s)
Maschhoff, Kevin Robert
Issue Date
1986
Doctoral Committee Chair(s)
Granato, A.V.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
ultrasonic study
trapped hydrogen tunneling systems
Nb
Ta
sound velocity
Language
en
Abstract
The properties of trapped hydrogen tunneling systems in Nb
and the analogous systems, H in Ta, and D in Nb have been
studied with ultrasonic techniques at low temperature. Attenuation
due to H in Ta was measured between 0.5 K and 10 K for
frequencies between 10 MHz and 55 MHz. The sound velocity
change due to H in Nb was measured in both the normal and
superconducting state at 10.8 MHz and 33 MHz at temperatures
between 0.5 K and 18 K. The attenuation and velocity change due
to trapped D in Nb was measured in both the superconducting and
normal states for two concentrations of oxygen trapping
impurity.
It is concluded that nearly all of the experimentally
observed properties of this system can be understood in terms of
a two-level model. All parameters of the model can be derived
from the velocity data.
Several features of the response predicted by the model
have been compared to the ultrasonic data on H and D tunneling
systems. The observed relaxation rate of H in Ta was found to
be consistent with an electronic mechanism for the relaxation.
The most significant result found was that driving the Nb host
into the normal state reduces the energy splitting of the
iv
tunneling systems as predicted for Nb-0-H. Qualitative differences
between the velocity data at high and low OH concentrations
have been attributed to a distribution of internal
strain created by the 0 impurities. The width of the distribution
was derived from the velocity data. It was found that
the tunneling parameter for D is much smaller than it is for H.
This enhances the effects of internal strain on D tunneling
systems and leads to relaxation spectra that are much broader
for D than they are for H.
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