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Reference : UMR7590-EGLBOU-001
Workplace : PARIS 05
Date of publication : Tuesday, June 8, 2021
Scientific Responsible name : Eglantine BOULARD (CNRS, IMPMC) and Gérald LELONG (Sorbonne Université, IMPMC)
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Oxygen is the most abundant element of the Earth (> 44 %). It's a major element of rock forming minerals as well as volatile compounds such as CO2 and water. Its valence state, speciation and oxidation state within the Earth's interior is however poorly studied. All current geochemical models assume that the oxide ion O2- (oxygen with an oxidation state of -II) is the unvariant anion of the Earth's mantle minerals. The recent discovery of peroxide type phases (that contain O22- groups, with an oxidation state of -I of oxygen) now challenges this general conception. The stability of these phases below 1800 km depth, may influence our understanding of geodynamical cycles of water, oxygen and hydrogen. They also represent new candidates for the deep mantle seismological heterogeneities.
The aim of the present thesis project is to determine the conditions of pressure, temperature, and composition to stabilize this -I valence state of oxygen in the deep Earth. To do so, it is necessary to determine the phase diagram of the chemical system Fe-O-H, and in a second part to test the possibility of solid solutions with the Earth's mantle major cations. The experimental work will be performed in laser heated diamond anvil cell. Special attention will be devoted to the crystallography and crystal chemistry description of the high pressure phases; To do so, we will combine cutting edge probes (for in situ synchrotron-based X-Ray Diffraction and X-Ray Raman Scattering) with ab initio calculation in order to fully interpret the spectroscopic signatures. In addition, it will be possible to use Density Functional Theory (DFT) calculations to guide the experimental work.
This experimental and theoretical work will provide new insights on the Earth's deep water, oxygen and hydrogen geochemical cycle as well as the mineralogy at or close to the core-mantle boundary.
• Keywords : Earth's mantle, geodynamical water cycle, phase diagram, high pressure and temperature experiments, ab initio calculation, DFT calculation
• Profile : we are looking for highly motivated candidate by both experimental and theoretical work for a project at the frontier between material science and planetology. The candidate should hold a master degree in geophysic, geochemistry or material science.
The thesis will be carried out at the Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), a research unit supported by the Centre National de la Recherche Scientifique (CNRS), Sorbonne Université and the Muséum National d'Histoire Naturelle (MNHN). IMPMC counts researchers from different backgrounds in condensed matter physics, material science, biology and mineralogy, offering a truly multidisciplinary research setting. IMPMC has historical links with synchrotron facilities and traditional expertise in high-pressure experimentations such as diamond anvil cell and large volume press technologies. On site we have access to a complete synthesis laboratory: a double-sided laser-heating diamond-anvil cell laboratory and a large volume laboratory (piston-cylinder, Paris Edinburg presses, multi-anvil press) laboratory, a femtosecond laser micro-machining facility; as well as a large number of analytical platforms such as electronic microscopes (SEM and TEM), a focused ion beam (FIB), x-ray diffraction equipments, picosecond acoustics setup, and various optical spectrometers (Raman, infrared, Brillouin spectrometers).
The thesis work will be performed within the research team MP3, under the join supervision of Eglantine Boulard (MP3 group principal-investigator of the ANR OXYGEN program which will financially support this PhD) and Gérald Lelong (Verres et Minéraux team member), and within the Doctoral School ED 397, Physique et Chimie des Matériaux at Sorbonne Université.
We propose a challenging and formative PhD project, with a truly interdisciplinary character that mixes experimentation at extreme conditions with modeling, and has both a systematic and development character. The successful candidate will gain competences in condensed matter physics, material science and planetary science. He/She will profit of the state-of-the-art experimental facilities available at IMPMC and on large instrument installations with which IMPMC is in close collaboration.
Constraints and risks
The proposed experimental activity will be carried out at IMPMC and at synchrotron facilities. Access to third generation synchrotron facilities is granted on the basis of competitive proposals but based on the scientific merit of our proposals, our scientific output in high-profile journals, and the personal collaboration with several beamline scientists, the access to synchrotron facilities is not foreseen as limiting factor to the success of the project. Some beamtime are already allocated and planned for the first year of the PhD.
Performing experiments at extreme pressure and temperature conditions is never easy, and the collection of high-quality data requires extreme care in sample preparation, characterization and conditioning, together with stringent measurements and analysis protocols.
Several national and international (mainly Europe and USA) trips have to be expected to perform measurements as well as to participate to meetings and conferences.
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