TY  - JOUR
A1  - Cerantola, Valerio
A1  - Wilke, Max
A1  - Kantor, Innokenty
A1  - Ismailova, Leyla
A1  - Kupenko, Ilya
A1  - McCammon, Catherine
A1  - Pascarelli, Sakura
A1  - Dubrovinsky, Leonid S.
T1  - Experimental investigation of FeCO3 (siderite) stability in Earth's lower mantle using XANES spectroscopy
JF  - American mineralogist : an international journal of earth and planetary materials
N2  - We studied FeCO3 using Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy at pressures up to 54 GPa and temperatures above 2000 K. First-principles calculations of Fe at the K-edge in FeCO3 were performed to support the interpretation of the XANES spectra. The variation of iron absorption edge features with pressure and temperature in FeCO3 matches well with recently reported observations on FeCO3 at extreme conditions, and provides new insight into the stability of Fe-carbonates in Earth's mantle. Here we show that at conditions of the mid-lower mantle, ~50 GPa and ~2200 K, FeCO3 melts and partially decomposes to high-pressure Fe3O4. Carbon (diamond) and oxygen are also inferred products of the reaction. We constrained the thermodynamic phase boundary between crystalline FeCO3 and melt to be at 51(1) GPa and ~1850 K. We observe that at 54(1) GPa, temperature-induced spin crossover of Fe2+ takes place from low to high spin such that at 1735(100) K, all iron in FeCO3 is in the high-spin state. A comparison between experiment and theory provides a more detailed understanding of FeCO3 decomposition observed in X-ray absorption spectra and helps to explain spectral changes due to pressure-induced spin crossover in FeCO3 at ambient temperature.
KW  - Deep carbon cycle
KW  - siderite
KW  - decomposition
KW  - melting
KW  - spin transition
KW  - Earth in Five Reactions: A Deep Carbon Perspective
Y1  - 2019
U6  - https://doi.org/10.2138/am-2019-6428
SN  - 0003-004X
SN  - 1945-3027
VL  - 104
IS  - 8
SP  - 1083
EP  - 1091
PB  - Mineralogical Society of America
CY  - Chantilly
ER  - 
TY  - JOUR
A1  - Nunez Valdez, Maribel
A1  - Efthimiopoulos, Ilias
A1  - Taran, Michail
A1  - Mueller, Jan
A1  - Bykova, Elena
A1  - McCammon, Catherine
A1  - Koch-Müller, Monika
A1  - Wilke, Max
T1  - Evidence for a pressure-induced spin transition in olivine-type LiFePO4 triphylite
JF  - Physical review : B, Condensed matter and materials physics
N2  - We present a combination of first-principles and experimental results regarding the structural and magnetic properties of olivine-type LiFePO4 under pressure. Our investigations indicate that the starting Pbnm phase of LiFePO4 persists up to 70 GPa. Further compression leads to an isostructural transition in the pressure range of 70-75 GPa, inconsistent with a former theoretical study. Considering our first-principles prediction for a high-spin to low-spin transition of Fe2+ close to 72 GPa, we attribute the experimentally observed isostructural transition to a change in the spin state of Fe2+ in LiFePO4. Compared to relevant Fe-bearing minerals, LiFePO4 exhibits the largest onset pressure for a pressure-induced spin state transition.
Y1  - 2018
U6  - https://doi.org/10.1103/PhysRevB.97.184405
SN  - 2469-9950
SN  - 2469-9969
VL  - 97
IS  - 18
PB  - American Physical Society
CY  - College Park
ER  -