Spectroscopic and ab initio studies of the pressure-induced Fe2+ high-spin-to-low-spin electronic transition in natural triphylite-lithiophilite
- Using optical absorption and Raman spectroscopic measurements, in conjunction with the first-principles calculations, a pressure-induced high-spin (HS)-to-low-spin (LS) state electronic transition of Fe2+ (M2-octahedral site) was resolved around 76-80GPa in a natural triphylite-lithiophilite sample with chemical composition (LiFe0.7082+Mn0.292PO4)-Li-M1-Fe-M2 (theoretical composition (LiFe0.52+Mn0.5PO4)-Li-M1-Fe-M2). The optical absorption spectra at ambient conditions consist of a broad doublet band with two constituents (1) (similar to 9330cm(-1)) and (2) (similar to 7110cm(-1)), resulting from the electronic spin-allowed transition (T2gEg)-T-5-E-5 of octahedral (HSFe2+)-Fe-M2. Both (1) and (2) bands shift non-linearly with pressure to higher energies up to similar to 55GPa. In the optical absorption spectrum measured at similar to 81GPa, the aforementioned HS-related bands disappear, whereas a new broadband with an intensity maximum close to 16,360cm(-1) appears, superimposed on the tail of the high-energy ligand-to-metal O2-Fe2+Using optical absorption and Raman spectroscopic measurements, in conjunction with the first-principles calculations, a pressure-induced high-spin (HS)-to-low-spin (LS) state electronic transition of Fe2+ (M2-octahedral site) was resolved around 76-80GPa in a natural triphylite-lithiophilite sample with chemical composition (LiFe0.7082+Mn0.292PO4)-Li-M1-Fe-M2 (theoretical composition (LiFe0.52+Mn0.5PO4)-Li-M1-Fe-M2). The optical absorption spectra at ambient conditions consist of a broad doublet band with two constituents (1) (similar to 9330cm(-1)) and (2) (similar to 7110cm(-1)), resulting from the electronic spin-allowed transition (T2gEg)-T-5-E-5 of octahedral (HSFe2+)-Fe-M2. Both (1) and (2) bands shift non-linearly with pressure to higher energies up to similar to 55GPa. In the optical absorption spectrum measured at similar to 81GPa, the aforementioned HS-related bands disappear, whereas a new broadband with an intensity maximum close to 16,360cm(-1) appears, superimposed on the tail of the high-energy ligand-to-metal O2-Fe2+ charge-transfer absorption edge. We assign this new band to the electronic spin-allowed dd-transition (1)A(1g)(1)T(1g) of LS Fe2+ in octahedral coordination. The high-pressure Raman spectra evidence the Fe2+ HS-to-LS transition mainly from the abrupt shift of the P-O symmetric stretching modes to lower frequencies at similar to 76GPa, the highest pressure achieved in the Raman spectroscopic experiments. Calculations indicated that the presence of Mn-M2(2+) simply shifts the isostructural HS-to-LS transition to higher pressures compared to the triphylite Fe-M2(2+) end-member, in qualitative agreement with our experimental observations.…
Author details: | Michail N. Taran, Maribel Nunez Valdez, Ilias EfthimiopoulosORCiD, J. Müller, Hans-Josef Reichmann, Max WilkeORCiDGND, Monika Koch-MüllerORCiD |
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DOI: | https://doi.org/10.1007/s00269-018-1001-y |
ISSN: | 0342-1791 |
ISSN: | 1432-2021 |
Title of parent work (English): | Physics and Chemistry of Minerals |
Publisher: | Springer |
Place of publishing: | New York |
Publication type: | Article |
Language: | English |
Date of first publication: | 2019/09/10 |
Publication year: | 2019 |
Release date: | 2021/03/23 |
Tag: | DFT; High pressure; Infrared; Optical absorption spectroscopy; Phosphates; Raman; Spin transition; Triphylite |
Volume: | 46 |
Issue: | 3 |
Number of pages: | 14 |
First page: | 245 |
Last Page: | 258 |
Funding institution: | Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [Ko1260/18, Wi2000/10]; Julich Supercomputing Center (JSC) [hpo24] |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Geowissenschaften |
DDC classification: | 5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften |
Peer review: | Referiert |