This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/25652
Description
Title
Thermal vacancies in solid helium-3
Author(s)
Heald, Steve Michael
Issue Date
1976
Doctoral Committee Chair(s)
Simmons, R.O.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Thermal Vacancies
Solid Helium-3
Helium Crystals
x-ray lattice parameter
bcc helium
Language
en
Abstract
Thermal vacancy concentrations in crystals of 3He have been determined from high precision measurements of the tem3
perature dependence of the x-ray lattice parameter. Bcc He 3
was studied for molar volumes ranging from 20.3 to 24.8 cm ; mole for which the melting temperatures range from 2.36 to
0.435K. It was found to contain about 0.5% thermal vacancies at melting, essentially independent of molar volume. A single hcp 3He crystal (18.8 cm3;mole) was studied, and was found to have 0.1% thermal vacancies at melting. From the measured vacancy concentrations free energies of formation are obtained and compared with results from NMR experiments. These comparisons suggest that in the bcc phase vacancies move by a
tunneling process, while in the hcp phase their motion is
thermally activated.
Free volumes of formation are found from a comparison of the measured vacancy concentrations with existing thermal expansion and compressibility measurements. In the bcc phase the formation free volume is. found to vary from 0.4 va at
20 cm3 / mole to 0.2 va at 24.5 cm3 / mole, where va is an atomic
volume.
The apparent heat capacity of the vacancies is calculated and found to be unreasonably high. The possibility of vacancy non-localization is examined by applying a model based on the work of Hetherington to the volume of formation and vacancy heat capacity results.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
