TY  - JOUR
A1  - Kaa, Johannes M.
A1  - Sternemann, Christian
A1  - Appel, Karen
A1  - Cerantola, Valerio
A1  - Preston, Thomas R.
A1  - Albers, Christian
A1  - Elbers, Mirko
A1  - Libon, Lelia
A1  - Makita, Mikako
A1  - Pelka, Alexander
A1  - Petitgirard, Sylvain
A1  - Plückthun, Christian
A1  - Roddatis, Vladimir
A1  - Sahle, Christoph J.
A1  - Spiekermann, Georg
A1  - Schmidt, Christian
A1  - Schreiber, Anja
A1  - Sakrowski, Robin
A1  - Tolan, Metin
A1  - Wilke, Max
A1  - Zastrau, Ulf
A1  - Konopkova, Zuzana
T1  - Structural and electron spin state changes in an x-ray heated iron carbonate system at the Earth's lower mantle pressures
JF  - Physical review research
N2  - The determination of the spin state of iron-bearing compounds at high pressure and temperature is crucial for our understanding of chemical and physical properties of the deep Earth. Studies on the relationship between the coordination of iron and its electronic spin structure in iron-bearing oxides, silicates, carbonates, iron alloys, and other minerals found in the Earth's mantle and core are scarce because of the technical challenges to simultaneously probe the sample at high pressures and temperatures. We used the unique properties of a pulsed and highly brilliant x-ray free electron laser (XFEL) beam at the High Energy Density (HED) instrument of the European XFEL to x-ray heat and probe samples contained in a diamond anvil cell. We heated and probed with the same x-ray pulse train and simultaneously measured x-ray emission and x-ray diffraction of an FeCO3 sample at a pressure of 51 GPa with up to melting temperatures. We collected spin state sensitive Fe K beta(1,3) fluorescence spectra and detected the sample's structural changes via diffraction, observing the inverse volume collapse across the spin transition. During x-ray heating, the carbonate transforms into orthorhombic Fe4C3O12 and iron oxides. Incipient melting was also observed. This approach to collect information about the electronic state and structural changes from samples contained in a diamond anvil cell at melting temperatures and above will considerably improve our understanding of the structure and dynamics of planetary and exoplanetary interiors.
Y1  - 2022
U6  - https://doi.org/10.1103/PhysRevResearch.4.033042
SN  - 2643-1564
VL  - 4
IS  - 3
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - BOOK
A1  - Albers, Marion
A1  - Appel, Ivo
A1  - Bauer, Hartmut
A1  - von Bogdandy, Armin
A1  - Britz, Gabriele
A1  - Bumke, Wolfgang
A1  - Fehling, Michael
A1  - Gusy, Christoph
A1  - Hermes, Georg
A1  - Hill, Hermann
A1  - Hoffmann-Riem, Wolfgang
A1  - Holznagel, Bernd
A1  - Köck, Wolfgang
A1  - Ladeur, Karl-Heinz
A1  - Michael, Lothar
A1  - Pitschas, Rainer
A1  - Röhl, Hans Christian
A1  - Rossen-Stahlfeld, Helge
A1  - Sachs, Michael
A1  - Sachsofsky, Ute
A1  - Schmidt-Aßmann, Eberhard
A1  - Schneider, Jens-Peter
A1  - Vesting, Thomas
ED  - Hoffmann-Riem, Wolfgang
ED  - Schmidt-Aßmann, Eberhard
ED  - Voßkuhle, Andreas
T1  - Grundlagen des Verwaltungsrechts : Bd. II Informationsordnung, Verwaltungsverfahren, Handlungsformen
Y1  - 2008
SN  - 978-3-406-54718-8
VL  - 2
PB  - Beck
CY  - München
ER  - 
TY  - JOUR
A1  - Krstulović, Marija
A1  - Rosa, Angelika D.
A1  - Ferreira Sanchez, Dario
A1  - Libon, Lélia
A1  - Albers, Christian
A1  - Merkulova, Margarita
A1  - Grolimund, Daniel
A1  - Irifune, Tetsuo
A1  - Wilke, Max
T1  - Effect of temperature on the densification of silicate melts to lower earth's mantle conditions
JF  - Physics of the earth and planetary interiors
N2  - Physical properties of silicate melts play a key role for global planetary dynamics, controlling for example volcanic eruption styles, mantle convection and elemental cycling in the deep Earth. They are significantly modified by structural changes at the atomic scale due to external parameters such as pressure and temperature or due to chemistry. Structural rearrangements such as 4- to 6-fold coordination change of Si with increasing depth may profoundly influence melt properties, but have so far mostly been studied at ambient temperature due to experimental difficulties. In order to investigate the structural properties of silicate melts and their densification mechanisms at conditions relevant to the deep Earth's interior, we studied haplo basaltic glasses and melts (albite-diopside composition) at high pressure and temperature conditions in resistively and laser-heated diamond anvil cells using X-ray absorption near edge structure spectroscopy. Samples were doped with 10 wt% of Ge, which is accessible with this experimental technique and which commonly serves as a structural analogue for the network forming cation Si. We acquired spectra on the Ge K edge up to 48 GPa and 5000 K and derived the average Ge-O coordination number NGe-O, and bond distance RGe-O as functions of pressure. Our results demonstrate a continuous transformation from tetrahedral to octahedral coordination between ca. 5 and 30 GPa at ambient temperature. Above 1600 K the data reveal a reduction of the pressure needed to complete conversion to octahedral coordination by ca. 30 %. The results allow us to determine the influence of temperature on the Si coordination number changes in natural melts in the Earth's interior. We propose that the complete transition to octahedral coordination in basaltic melts is reached at about 40 GPa, corresponding to a depth of ca. 1200 km in the uppermost lower mantle. At the core-mantle boundary (2900 km, 130 GPa, 3000 K) the existence of non-buoyant melts has been proposed to explain observed low seismic wave velocity features. Our results highlight that the melt composition can affect the melt density at such extreme conditions and may strongly influence the structural response.
KW  - Silicate melts
KW  - Densification
KW  - High pressure and high temperature;
KW  - XANES
KW  - Coordination number
KW  - Ultra-low velocity zones
Y1  - 2022
U6  - https://doi.org/10.1016/j.pepi.2021.106823
SN  - 0031-9201
SN  - 1872-7395
VL  - 323
PB  - Elsevier
CY  - Amsterdam
ER  -