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Water Incorporation in Wadsleyite and Ringwoodite: Effect on Phase Stability and Structure

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Water Incorporation in Wadsleyite and Ringwoodite: Effect on Phase Stability and Structure Water incorporation in wadsleyite and ringwoodite: effect on phase stability and structure vorgelegt von Dipl.-Ing. Maria Mrosko aus Bad Muskau von der Fakultät VI – Planen Bauen Umwelt der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor der Naturwissenschaften - Dr. rer. nat. - genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof. Dr. Gerhard Franz Gutachterin: Prof. Dr. Monika Koch-Müller Gutachter: Prof. Dr. Wilhelm Heinrich Gutachter: Prof. Dr. Eugen Libowitzky Tag der wissenschaftlichen Aussprache: 18. Oktober 2013 Berlin 2013 D83 Table of contents Summary...............................................................................................................................3 Zusammenfassung................................................................................................................5 Introduction ..........................................................................................................................7 Chapter 1 ............................................................................................................................21 Abstract...........................................................................................................................22 Introduction ....................................................................................................................22 Experimental and analytical methods ...........................................................................25 Results.............................................................................................................................30 Discussion .......................................................................................................................34 Concluding remarks........................................................................................................39 Acknowledgements .........................................................................................................40 Figures ............................................................................................................................40 References .......................................................................................................................48 Chapter 2 ............................................................................................................................51 Abstract...........................................................................................................................52 Introduction ....................................................................................................................53 Experimental and analytical methods ...........................................................................54 Results.............................................................................................................................57 Discussion .......................................................................................................................60 Acknowledgements .........................................................................................................65 Figures ............................................................................................................................65 References .......................................................................................................................69 Chapter 3 ............................................................................................................................72 Abstract...........................................................................................................................73 Introduction ....................................................................................................................73 Experimental methods....................................................................................................74 Results.............................................................................................................................76 Discussion .......................................................................................................................77 Figures ............................................................................................................................79 References .......................................................................................................................86 Chapter 4 ............................................................................................................................89 Abstract...........................................................................................................................90 Short summary ...............................................................................................................90 References .......................................................................................................................93 Chapter 5 ............................................................................................................................95 Introduction ....................................................................................................................95 Low temperature heat capacity (PPMS) ........................................................................95 High-temperature heat capacity (DSC)..........................................................................97 Final Heat capacity.........................................................................................................98 Evaluation of the data and outlook ................................................................................99 References .....................................................................................................................100 Synthesis of results...........................................................................................................102 Discussion of the applied methods ...............................................................................102 Concluding statements .................................................................................................107 References .....................................................................................................................109 Danke ................................................................................................................................110 Appendix AI - Work-sharing agreement ..........................................................................111 Appendix AII - Eidesstattliche Versicherung ..................................................................113 Appendix AIII - Lebenslauf ..............................................................................................114 2 Summary This PhD project about the effect of water incorporation on the structure and phase stability of wadsleyite and ringwoodite is integrated in the DFG priority program 1236 ‚Strukturen und Eigenschaften von Kristallen bei extrem hohen Drücken und Temperaturen’. The corresponding research work was conducted at the Helmholtz Centre Potsdam, German Research Centre for Geosciences, GFZ, Department 3.3 Chemistry and Physics of Earth Materials. Seismic profiles of the Earth’s inner structure reveal discontinuities in the p- and s-wave velocities at certain depths. The discontinuities at 410, 520, and 660 km depth are assigned to the transformations of the (Mg,Fe)2SiO4-polymorphs olivine (!-form) to wadsleyite (") and ringwoodite (#). However, the observed depths and widths of these velocity jumps are not constant but vary on a global scale, especially in the case of d520. The reason for that has been subject matter of various discussions. The main issue of this PhD work is to evaluate the effect of hydrogen on the structure and phase stabilities of wadsleyite and ringwoodite and to investigate if the incorporation of water in these minerals might be responsible for the observed depths variations of d520. The experimental approach included the performance of high-pressure syntheses (varied parameters: pressure, water content, composition, oxygen fugacity) in a multi-anvil apparatus and an extensive investigation of the synthesized material. X-ray diffraction techniques and electron microprobe analyses were applied to identify the samples and define their structure and composition in detail. However, the main focus of the work was to localize and quantify hydrogen (and iron (Fe)) within the samples by spectroscopic techniques and to evaluate the effect of the incorporated species on the structure and phase stabilities of wadsleyite and ringwoodite. In the first part of this study the pressure-depending behavior of dry vs. hydrous iron free wadsleyite was investigated by IR spectroscopy. Thereby we could show that the incorporation of hydrogen shifts the phase transition from orthorhombic to monoclinic wadsleyite about 1.6 GPa to lower pressures. In the second part, the location of hydrogen in ringwoodite was investigated. We found x that the main mechanisms are related to octahedral vacancies [VMg(OH)2] and the x hydrogarnet substitution [VSi(OH)4] . The third part of the work was related to the effect of non-hydrostatic pressure conditions on the structure of hydrous ringwoodite. Thereby we could show that such conditions lead to a stress-induced proton disorder. 3 In the fourth part we investigated the direct
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