Investigation of Structural Phase Transitions in Minerals and Analogue Systems by High-temperature Magic-angle-spinning Nuclear Magnetic Resonance Spectroscopy PDF Download
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Author: Brian L. Phillips
Publisher:
ISBN:
Category :
Languages : en
Pages : 190
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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$spcirc$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.
Author: Brian L. Phillips
Publisher:
ISBN:
Category :
Languages : en
Pages : 190
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Book Description
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$spcirc$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.
Author: Ian Parsons
Publisher: Springer Science & Business Media
ISBN: 9780792327226
Category : Science
Languages : en
Pages : 702
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Book Description
Feldspar minerals make up 60% of the crust of the Earth. They are stable in the upper mantle, and are so abundant in the crust that they form the basis of the classification of igneous rocks. At the surface, feldspars weather to form clay minerals which are the most important mineral constituent of soils. The articles in this book review the chemical reactions of feldspars over the whole sweep of pressure and temperature regimes in the outer Earth, and describe the fundamental aspects of crystal structure which underlie their properties. The book covers intracrystalline reactions, such as order-disorder transformations and exsolution, and transfer of stable and radiogenic isotopes, which can be interpreted to provide insights into the thermal history of rocks. It is suitable for final year undergraduates or research workers.
Author:
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Category : Dissertations, Academic
Languages : en
Pages : 734
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Author: Yuehui Xiao
Publisher:
ISBN:
Category :
Languages : en
Pages :
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This thesis contributes to the application of nuclear magnetic resonance (NMR) techniques in studying structural phase transitions (SPT's) of the SiO$sb2$ cristobalite and SiO$sb2$ and AlPO$sb4$ tridymite polymorphs. The structural properties and SPT's of these phases have been of mineralogical, physical and industrial interest for decades. However, the microscopic characteristics of the SPT's and the origins of the commonly observed structural disorder in the high temperature phases have been poorly known. NMR techniques call provide important information concerning the temperature variation of the short-range structural parameters through SPT's. Moreover, the dynamical behavior of high temperature phases in the NMR frequency range ($sim$1-500 MHz) can sometimes be uniquely elucidated by relaxation rate measurements and spectral simulation. The work presented here includes in situ high temperature $sp{29}$Si, $sp{31}$P and $sp{27}$Al NMR results for cristobalite (Chapter II), chemically stabilized $beta$-cristobalite (Chapter III), various tridymite polymorphs (MC and PO, Chapter IV; MX-1 Chapter V; AlPO$sb4,$ Chapter VI) and a spin-lattice relaxation investigation of the dynamic properties for the high temperature SiO$sb2$ and AlPO$sb4$ tridymite phases (Chapter VII).
Author: Subrata Ghose
Publisher:
ISBN:
Category : Mineralogy
Languages : en
Pages : 270
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Author:
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 340
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Author: Yuehui Xiao
Publisher:
ISBN:
Category :
Languages : en
Pages : 330
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Author:
Publisher:
ISBN:
Category : Dissertation abstracts
Languages : en
Pages : 768
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Author: S. Ghose
Publisher: Springer
ISBN: 9781461238638
Category : Science
Languages : en
Pages : 244
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Author: Petrus Johannes Dirken
Publisher: Faculteit Aardwetenschappen Universiteit Utrecht
ISBN:
Category : Science
Languages : en
Pages : 92
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Met een samenvatting in het Nederlands