Pressure driven spin transition in siderite and magnesiosiderite single crystals

Abstract

Iron-bearing carbonates are candidate phases for carbon storage in the deep Earth and may play an important role for the Earth’s carbon cycle. To elucidate the properties of carbonates at conditions of the deep Earth, we investigated the pressure driven magnetic high spin to low spin transition of synthetic siderite FeCO3 and magnesiosiderite (Mg0.74Fe0.26)CO3 single crystals for pressures up to 57 GPa using diamond anvil cells and x-ray Raman scattering spectroscopy to directly probe the iron 3d electron configuration. An extremely sharp transition for siderite single crystal occurs at a notably low pressure of 40.4 ± 0.1 GPa with a transition width of 0.7 GPa when using the very soft pressure medium helium. In contrast, we observe a broadening of the transition width to 4.4 GPa for siderite with a surprising additional shift of the transition pressure to 44.3 ± 0.4 GPa when argon is used as pressure medium. The difference is assigned to larger pressure gradients in case of argon. For magnesiosiderite loaded with argon, the transition occurs at 44.8 ± 0.8 GPa showing similar width as siderite. Hence, no compositional effect on the spin transition pressure is observed. The spectra measured within the spin crossover regime indicate coexistence of regions of pure high- and low-spin configuration within the single crystal.

Polymerized 4-Fold Coordinated Carbonate Melts in the Deep Mantle

“…The lowest transition P from 3 to 4-fold C in FeCO 3 amongst carbonates justifies its choice as the first composition to investigate. Not only this transition occurs at less challenging experimental conditions, but it might be driven by Fe high spin to low spin transition at 40.4 GPa (Weis et al, 2017), a consequence of which being the large enrichment in Fe of (Mg,Fe)carbonates coexisting with bridgmanite to almost pure FeCO 3 (Lobanov et al, 2015). Besides, high Fe concentration stabilizes (Ca,Mg,Fe) IV CO 3 with respect to single cation 3-fold carbonates at mid mantle conditions (30-50 GPa) (Solomatova and Asimow, 2018).…”

Spin Transition of Iron in Deep‐Mantle Ferromagnesite

“…Liu et al, 2019), which results in a reduction in the unit-cell volume and significant changes in vibrational properties (Cerantola et al, 2015;Lin et al, 2012;Spivak et al, 2014;Weis et al, 2017). Thus far, the Fe 2+ spin transition in (Mg,Fe)CO 3 has been diagnosed based on the abrupt reduction of the unit-cell volume in XRD measurements (Farfan et al, 2012;Lavina et al, 2009;Lin et al, 2012;Liu et al, 2014Liu et al, , 2015Nagai et al, 2010) and significant changes in the Raman shifts of vibrational modes in both optical and X-ray Raman spectroscopic studies (Cerantola et al, 2015;Fu et al, 2017;Lin et al, 2012;Spivak et al, 2014;Weis et al, 2017). Across the Fe 2+ spin transition, the reduction of total spin momentum in Fe 2+ can be captured by X-ray emission spectroscopy (Mattila et al, 2007).…”

“…The starting pressure and pressure ranges of the Fe 2+ spin transition in (Mg,Fe)CO 3 are sensitive to the hydrostatic condition in high-pressure DAC experiments: When relatively hydrostatic helium pressure medium is used in DAC experiments, the spin transition in FeCO 3 occurs at 40.4 ± 0.1 GPa with a transition width of 0.7 GPa at 300 K (Weis et al, 2017). In contrast, the spin transition pressure changes to 44.3 ± 0.4 GPa and the transition width broadens to 4.4 GPa when argon is used as the pressure medium (Weis et al, 2017). The Earth's mantle is mostly under relatively hydrostatic compression condition, except regions near subducting slabs where stress could be ~100-300 MPa (e.g.…”

“…The spin transition in (Mg,Fe)CO 3 is associated with a volume collapse due to the reconfiguration of the Figure 12.2 A summary of the reported pressure ranges for the Fe 2+ spin transition in (Mg, Fe)CO 3 samples observed using various techniques at 300 K. Each vertical line with bars marks the pressure range of mixed-spin state for the corresponding composition. Black lines: XRD (Lavina et al, 2009;Nagai et al, 2010;Lin et al, 2012;Farfan et al, 2012;Liu et al, 2014Liu et al, , 2015; red line: Mössbauer (Cerantola et al, 2015, Liu et al, 2019; pink line: optical Raman (Lin et al 2012); orange line: X-ray Raman (Weis et al, 2017); blue lines: optical absorption spectroscopy (Lobanov et al, 2015(Lobanov et al, , 2016Taran et al, 2017); green lines: DFT (Hsu & Huang, 2016). For simplicity, some previous DAC results obtained at relatively nonhydrostatic conditions, which can influence the spin transition pressure, are not shown here.…”

Quantum shape effects and novel thermodynamic behaviors at nanoscale

“…By controlling these size variables it is possible to manipulate and tailor the certain features of confined systems (e.g. semiconductors, metals, superconductors, topological insulators and ultracold gases) in a desired way [21][22][23][24][25][26][27][28][29][30][31] . QSE give rise also to phenomena such as thermosize effects and specific heat oscillations which can be used in nanoscale energy conversion and storage technologies 19,[32][33][34] .…”