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Title:Thermal vacancies in solid helium-3
Author(s):Heald, Steve Michael
Doctoral Committee Chair(s):Simmons, R.O.
Department / Program:Physics
Subject(s):Thermal Vacancies
Solid Helium-3
Helium Crystals
x-ray lattice parameter
bcc helium
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.
Issue Date:1976
Genre:Dissertation / Thesis
Rights Information:1976 Steve Michael Heald
Date Available in IDEALS:2011-07-05
Identifier in Online Catalog:2674288

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