University of Illinois Urbana-Champaign

Investigation of structural phase transitions in minerals and analogue systems by high-temperature magic-angle-spinning nuclear magnetic resonance spectroscopy

Phillips, Brian L.

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/2142/23717

Description

Title
Investigation of structural phase transitions in minerals and analogue systems by high-temperature magic-angle-spinning nuclear magnetic resonance spectroscopy
Author(s)
Phillips, Brian L.
Issue Date
1990
Doctoral Committee Chair(s)
Kirkpatrick, R. James
Department of Study
  • Mineralogy
  • Chemistry, Physical
  • Physics, Condensed Matter
Discipline
  • Mineralogy
  • Chemistry, Physical
  • Physics, Condensed Matter
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Date of Ingest
2011-05-07T14:24:28Z
Keyword(s)
  • Mineralogy
  • Chemistry, Physical
  • Physics, Condensed Matter
Language
eng
Abstract
  • This work comprises studies of structural phase transitions (SPT's) in three different phases (anorthite CaAl$\sb2$Si$\sb2$O$\sb8$, Sr$\sb2$SiO$\sb4$, and AlPO$\sb4$-cristobalite) via high-resolution nuclear magnetic resonance spectroscopy using mostly magic-angle spinning (MAS) techniques. The results provide important insight into each of these SPT's and illustrate the types of information that can be obtained about SPT's using MAS NMR spectroscopy.
  • Insight regarding structural changes for all three phases was obtained from the temperature dependence of the chemical shift. In Chapter 1 the temperature variation of the modulation wave in the incommensurate phase of Sr$\sb2$SiO$\sb4$ is determined from $\sp{29}$Si MAS NMR spectra. In Chapter 2 changes in the $\sp{29}$Si chemical shifts of anorthite show that its alumino-silicate framework transforms displacively at the P1-I1 transition. In Chapter 3 comparison of the $\sp{31}$P and $\sp{27}$Al chemical shifts of the $\alpha$ and $\beta$ phases of AlPO$\sb4$-cristobalite indicates that the $\beta$ phase is dynamically disordered. For anorthite and Sr$\sb2$SiO$\sb4$ the chemical shifts also provide a measure of the temperature evolution of the order parameter within the context of Landau theory. The ability of these methods to provide dynamical information from chemical shifts is demonstrated for $\beta$-AlPO$\sb4$-cristobalite for which time-averaging of chemical shifts produces values different than expected from the crystal structure, and for Sr$\sb2$SiO$\sb4$, for which the results show that the modulation wave is pinned up to 200$\sp\circ$C.
  • For anorthite and AlPO$\sb4$-cristobalite the chemical shift results are supplemented by spin-lattice relaxation measurements ($\sp{29}$Si in anorthite, $\sp{31}$P and $\sp{27}$Al in AlPO$\sb4$-cristobalite). For AlPO$\sb4$-cristobalite, a discontinuous increase of both the $\sp{31}$P and $\sp{27}$Al relaxation rates at the $\alpha-\beta$ transition and a logarithmic divergence of the $\sp{27}$Al relaxation rates in the $\beta$ phase support a dynamical order-disorder model for this transition. On the other hand, the lack of such an increase in the $\sp{29}$Si relaxation rates in anorthite across the P1-I1 transition support the conclusion that this transition is displacive.
Type of Resource
text
Permalink
http://hdl.handle.net/2142/23717
Copyright and License Information
Copyright 1990 Phillips, Brian L.

Owning Collections

Graduate Dissertations and Theses at Illinois PRIMARY
Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Geology