Interplay between H-bonding proton dynamics and Fe valence fluctuations in Fe 3 ( P O 4 ) 2 ( OH ) 2 at high pressure - Laboratoire Charles Coulomb (L2C) Access content directly
Journal Articles Physical Review B Year : 2023

Interplay between H-bonding proton dynamics and Fe valence fluctuations in Fe 3 ( P O 4 ) 2 ( OH ) 2 at high pressure

Abstract

We pressure tune the hydrogen bond in Fe-O-H⋅⋅⋅O-P structural segments of mixed-valence barbosalite (Fe 2+ Fe 3+ 2)(PO4)2(OH)2. Infrared spectroscopy evidences changes in softening of O-H stretch modes and excessive profile broadening onset below 10 GPa. Single-crystal X-ray diffraction shows pseudo-symmetrization of the original monoclinic unit cell concurs with these changes in the O-H vibrational mode. These are considered compelling indicators of proton delocalization onset below 10 GPa as hydrogen bonds are strengthened under pressure. Subsequently in the range 10−30 GPa, Fe Mössbauer spectroscopy discerns Fe 2+ ⇔ Fe 3+ valence fluctuations at proximate cations of the hydrogen bonds. When the original crystal potential at an Fe 2+ site is perturbed by proton delocalization at a ligand, electron exchange is induced along Fe 2+ →L→Fe 3+ pathways (ligand L = O or (OH)-of shared octahedral faces). Thus, (Fe 2+ Fe 3+ 2)(PO4)2(OH)2 under pressure exemplifies the interplay between proton (THz) and electron (MHz) dynamics on two disparate time scales in the same condensed phase.
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Dates and versions

hal-04037182 , version 1 (20-03-2023)

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G. Hearne, V. Ranieri, P. Hermet, J. Haines, O. Cambon, et al.. Interplay between H-bonding proton dynamics and Fe valence fluctuations in Fe 3 ( P O 4 ) 2 ( OH ) 2 at high pressure. Physical Review B, 2023, 107 (6), pp.L060302. ⟨10.1103/PhysRevB.107.L060302⟩. ⟨hal-04037182⟩
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