Valence state, coordination and incorporation of Ti and Cr into lower mantle phases: new insight from electron energy loss spectroscopy [Elektronische Ressource] / von Emil Stoyanov

Emil Stoyanov

Informations

• Publié par: friedrich-schiller-universitat_jena
• Publié le: 01 janvier 2007
• Nombre de lectures: 34
• Langue: English
• Poids de l'ouvrage: 329 Mo

Extrait

Valence state, coordination and
incorporation of Ti and Cr into lower
mantle phases: new insight from electron
energy-loss spectroscopy




Dissertation
zur Erlangung des akademischen Grades doctor rerum naturalium
(Dr. rer. nat.)












vorgelegt dem Rat der Chemisch-Geowissenschaftlichen Fakultät der
Friedrich-Schiller-Universität Jena

von Dipl.-Chem. Emil Stoyanov

geboren am 10.09.1978 in Plovdiv, Bulgarien


































Gutachter



1. Prof. Dr. Falko Langenhorst


2. Prof. Dr. (em.) Klaus Heide


Tag der öffentlichen Verteidigung: 31.01.2007 Emil Stoyanov
EELS of Ti and Cr in lower mantle phases
CONTENTS
Acknowledgements ............................................................................................... 4
Summary ............................................................................................................... 5
Zusammenfassung ................................................................................................. 7
1. Introduction and aims of the study .................................................................. 10
1.1. Introduction .................................................................................................. 10
1.2. Mineralogy and crystal chemistry of Ti and Cr in Earth and
planetary materials .................................................................................. 13
1.3. Aims of the study .................................................................................... 19
2. Samples and synthesis techniques ................................................................... 21
2.1. Preparation of standard materials for Ti and Cr valence
state calibration ...................................................................................... 21
2.1.1. Titanium standards ........................................................................ 21
2.1.2. Chromium standards ..................................................................... 22
2.2. Crystal structures of the titanium and chromium
standard materials ................................................................................... 24
2.2.1. Crystal structures of titanium standard materials .......................... 24
2.2.2. Crystal structures of chromium standard materials ....................... 28
2.3. High pressure-high temperature experiments:
Multi-anvil technique .............................................................................. 31
3. Analytical techniques ...................................................................................... 34
- 1 -Emil Stoyanov
EELS of Ti and Cr in lower mantle phases
3.1. Scanning electron microscopy (SEM) and electron
microprobe analysis (EPMA).................................................................. 34
3.2. Transmission electron microscopy (TEM) combined with energy
dispersive X-ray spectroscopy (EDX) and electron energy-loss
spectroscopy (EELS) .............................................................................. 36
3.2.1. Basic concepts of energy dispersive X-ray
spectroscopy (EDX) ...................................................................... 38

3.2.2. Basic concepts of electron energy-loss
spectroscopy (EELS) ..................................................................... 40
3.2.3. Electron energy-loss near-edge structures (ELNES) ..................... 42
3.2.4. Evaluation of the electron energy-loss
near-edge spectra ........................................................................... 44
4. Results and discussion .................................................................................... 46
4.1. Effect of valence state and coordination of Ti and
Cr on the spectral shape .......................................................................... 46
4.1.1. Effect of titanium valence state and
coordination on ELNES spectra .................................................... 47
4.1.2. Effect of chromium valence state and 51
4.2. Effect of site symmetry and polyhedral
distortion of Ti and Cr on the ELNES spectral shape .............................. 54
4.2.1. Effect of titanium site symmetry and
polyhedral distortion on ELNES spectra ........................................ 54
4.2.2. Effect of chromium site symmetry and
56
- 2 -Emil Stoyanov
EELS of Ti and Cr in lower mantle phases
4.3. Calibration techniques for the quantification Ti and Cr ........................... 57
4.3.1. Calibration method for the quantification
4+ of the Ti /ΣTi ratio ...................................................................... 57

4.3.2. Calibration method for the quantification
of Cr valence states ..................................................................... 60
4.4. Application of Ti and Cr ELNES to Lower mantle phases ..................... 63
4.4.1. Valence state and incorporation of Ti
and Cr in ferropericlase ................................................................ 64
4.4.1.1. Starting materials and experimental conditions.................... 64
4.4.1.2. Valence state and incorporation of
Ti and Cr in ferropericlase as function of
starting X ........................................................................................................................... 66FeO
4.4.1.3. Effect of pressure on the valence state and
incorporation of Ti and Cr in ferropericlase ......................... 79
4.4.1.4. Ti and Cr substitution mechanisms in
ferropericlase....................................................................... 83
4.4.2. Valence state and coordination of Ti and Cr
in silicate perovskite .................................................................... 84
4.4.3. Ti substitution mechanism in silicate perovskite ........................... 89
5. Conclusions ..................................................................................................... 91
Appendix A: Description of the parallel energy-loss
spectrometer Gatan 666 .................................................................. 94
Appendix B: Computer programs used for electron diffraction
analysis, and EELS and EDX spectra evaluation ............................ 96
Appendix C: Calculation of ionic radii in silicate perovskite
structure ......................................................................................... 98
References......................................................................................................... 100
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EELS of Ti and Cr in lower mantle phases
Acknowledgements
I am most grateful to my supervisor Prof. Dr. Falko Langenhorst. I would like to thank him for
providing me with such interesting topic, sharing always his great knowledge with me and for
some data and his help with the measurements. His helpful suggestions enriched my thesis with
several fruitful ideas.
I would like to thank the Deutsche Forschungsgemeinschaft (DFG), who funded this work (grant
LA 830/7-1). I thank the Bayerisches Geoinstitut (Bayreuth, Germany) where this study has been
largely performed, and appreciate the support by the International Graduate School “Oxides”
funded under the Elite Program Bavaria.
I am especially indebted to Dr. Dan Frost (BGI) and Dr. Gerd Steinle-Neumann (BGI). I am
grateful to Dan for the help with performing the multi-anvil experiments and for providing me
with some samples. We had very fruitful discussions about the experimental set-up and obtained
results. Gerd introduced me to various computational techniques and I thank him for our
discussions, for his scientific and friendly advices. Thank you.
My first steps in scanning electron microscopy were kindly assisted by Dr. Florian Heidelbach
(BGI). I am very thankful to Detlef Krauße (BGI) for the help with the microprobe operation.
The technical support I received from Gerti Golner (BGI) and Anke Potzel (BGI) for preparation
the starting materials has been extremely valuable. I thank the colleagues from Bayreuth and Jena
for their assistance and for the pleasant working atmosphere. Especially, I am grateful to Dr.
Nobuyoshi Miyajima (BGI) for his help, time and patience. I thank Ashima Saikia (BGI) for
providing me with some o