X-ray thermal diffuse scattering and its studies of lattice dynamics

Xu, Ruqing

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https://hdl.handle.net/2142/18627 Copy

Description

Title

X-ray thermal diffuse scattering and its studies of lattice dynamics

Author(s)

Xu, Ruqing

Issue Date

2011-01-21T22:52:17Z

Director of Research (if dissertation) or Advisor (if thesis)

Chiang, Tai-Chang

Doctoral Committee Chair(s)

Abbamonte, Peter M.

Committee Member(s)

• Chiang, Tai-Chang
• Goldbart, Paul M.
• Makins, Naomi C.R.

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• X-ray scattering
• thermal diffuse scattering
• lattice dynamics
• phonon

Abstract

X-ray scattering by lattice thermal vibrations give rise to thermal diffuse scattering (TDS). TDS contain valuable information about lattice dynamics of the scattering material. Historically, x-ray TDS was the first tool utilized by people in experimental determination of phonon dispersion relations. With the advent of synchrotron radiation technology, it has reemerged as an efficient probe for phonon studies in the recent decade. The scattering can be described with a semi-classical theory, and is often decomposed into first-order and high-order processes. First-order TDS, with a simple theoretical formula, is usually the dominating component and often used as an approximation to the total intensity. However, rigorous evaluation of high-order scattering has never been truly performed in the past, due largely to the apparent mathematical complexity of its expression. An algorithm aimed at resolving this difficulty is developed by the author, and proves to be successful. As a tool of phonon study, TDS was applied to the system of gallium-stabilized delta-plutonium. This material shows curious features in its phonon dispersion relation at room temperature; one of them was conjectured to exhibit further changes when temperature is lowered towards a structural phase transition at ~ 170 K. A TDS experiment was carried out to verify this prediction, yet analysis of the data showed that it was incorrect. In another major project, a new experimental approach was proposed to allow extraction of phonon dispersion information from measured TDS data without relying on any presumed force-constant models, which were required in previous TDS works and pose a limit to the method’s accuracy. The new approach determines frequencies of specific phonon modes based on the temperature-dependence of TDS intensities. A benchmark test of the approach on copper yielded excellent agreement with known phonon dispersion data.

Graduation Semester

2010-12

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http://hdl.handle.net/2142/18627

Copyright and License Information

Copyright 2010 Ruqing Xu

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