TY  - JOUR
A1  - Schifferle, Lukas
A1  - Lobanov, Sergey S.
T1  - Evolution of chemical bonding and spin-pairing energy in ferropericlase across Its spin transition
JF  - ACS Earth and Space Chemistry
N2  - The evolution of chemical bonding in ferropericlase, (Mg,Fe)O, with pressure may affect the physical and chemical properties of the Earth's lower mantle. Here, we report high-pressure optical absorption spectra of single-crystalline ferropericlase ((Mg0.87Fe0.13)O) up to 135 GPa. Combined with a re-evaluation of published partial fluorescence yield X-ray absorption spectroscopy data, we show that the covalency of the Fe-O bond increases with pressure, but the iron spin transition at 57-76.5 GPa reverses this trend. The qualitative crossover in chemical bonding suggests that the spin-pairing transition weakens the Fe-O bond in ferropericlase. We find, that the spin transition in ferropericlase is caused by both the increase of the ligand field-splitting energy and the decrease in the spin-pairing energy of high-spin Fe2+.
KW  - high-pressure
KW  - diamond anvil cell
KW  - covalency
KW  - bond strength
KW  - iron
KW  - spin
KW  - transition
Y1  - 2022
U6  - https://doi.org/10.1021/acsearthspacechem.2c00014
SN  - 2472-3452
VL  - 6
IS  - 3
SP  - 788
EP  - 799
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Armstrong, Michael R.
A1  - Radousky, Harry B.
A1  - Austin, Ryan A.
A1  - Tschauner, Oliver
A1  - Brown, Shaughnessy
A1  - Gleason, Arianna E.
A1  - Goldman, Nir
A1  - Granados, Eduardo
A1  - Grivickas, Paulius
A1  - Holtgrewe, Nicholas
A1  - Kroonblawd, Matthew P.
A1  - Lee, Hae Ja
A1  - Lobanov, Sergey
A1  - Nagler, Bob
A1  - Nam, Inhyuk
A1  - Prakapenka, Vitali
A1  - Prescher, Clemens
A1  - Reed, Evan J.
A1  - Stavrou, Elissaios
A1  - Walter, Peter
A1  - Goncharov, Alexander F.
A1  - Belof, Jonathan L.
T1  - Highly ordered graphite (HOPG) to hexagonal diamond (lonsdaleite) phase transition observed on picosecond time scales using ultrafast x-ray diffraction
JF  - Journal of applied physics
N2  - The response of rapidly compressed highly oriented pyrolytic graphite (HOPG) normal to its basal plane was investigated at a pressure of & SIM;80 GPa. Ultrafast x-ray diffraction using & SIM;100 fs pulses at the Materials Under Extreme Conditions sector of the Linac Coherent Light Source was used to probe the changes in crystal structure resulting from picosecond timescale compression at laser drive energies ranging from 2.5 to 250 mJ. A phase transformation from HOPG to a highly textured hexagonal diamond structure is observed at the highest energy, followed by relaxation to a still highly oriented, but distorted graphite structure following release. We observe the formation of a highly oriented lonsdaleite within 20 ps, subsequent to compression. This suggests that a diffusionless martensitic mechanism may play a fundamental role in phase transition, as speculated in an early work on this system, and more recent static studies of diamonds formed in impact events. Published by AIP Publishing.
Y1  - 2022
U6  - https://doi.org/10.1063/5.0085297
SN  - 0021-8979
SN  - 1089-7550
VL  - 132
IS  - 5
PB  - AIP Publishing
CY  - Melville
ER  - 
TY  - JOUR
A1  - Blanchard, Ingrid
A1  - Petitgirard, Sylvain
A1  - Laurenz, Vera
A1  - Miyajima, Nobuyoshi
A1  - Wilke, Max
A1  - Rubie, David C.
A1  - Lobanov, Sergey S.
A1  - Hennet, Louis
A1  - Morgenroth, Wolfgang
A1  - Tucoulou, Rémi
A1  - Bonino, Valentina
A1  - Zhao, Xuchao
A1  - Franchi, Ian
T1  - Chemical analysis of trace elements at the nanoscale in samples recovered from laser-heated diamond anvil cell experiments
JF  - Physics and chemistry of minerals
N2  - High pressure and high temperature experiments performed with laser-heated diamond anvil cells (LH-DAC) are being extensively used in geosciences to study matter at conditions prevailing in planetary interiors. Due to the size of the apparatus itself, the samples that are produced are extremely small, on the order of few tens of micrometers. There are several ways to analyze the samples and extract physical, chemical or structural information, using either in situ or ex situ methods. In this paper, we compare two nanoprobe techniques, namely nano-XRF and NanoSIMS, that can be used to analyze recovered samples synthetized in a LH-DAC. With these techniques, it is possible to extract the spatial distribution of chemical elements in the samples. We show the results for several standards and discuss the importance of proper calibration for the acquisition of quantifiable results. We used these two nanoprobe techniques to retrieve elemental ratios of dilute species (few tens of ppm) in quenched experimental molten samples relevant for the formation of the iron-rich core of the Earth. We finally discuss the applications of such probes to constrain the partitioning of trace elements between metal and silicate phases, with a focus on moderately siderophile elements, tungsten and molybdenum.
KW  - NanoSIMS
KW  - Nano-XRF
KW  - Diamond anvil cell
KW  - Focused ion beam
Y1  - 2022
U6  - https://doi.org/10.1007/s00269-022-01193-7
SN  - 0342-1791
SN  - 1432-2021
VL  - 49
IS  - 6
PB  - Springer
CY  - New York
ER  -