Protonated water layer in Ludlamite lamellar iron phosphate (Fe3(PO4)2·4H2O)
Abstract
The vibrational signature (Raman and IR) of natural ludlamite single crystals is discussed, along with the evolution of the Raman spectrum after heating to 90, 150, and 200 • C. The observation of broad "ABC" bands in the stretching mode region-characteristic of a strong, symmetric hydrogen bond-indicates the formation of H 2 O-H + -OH 2 (or H 5 O 2 + ) species. After deuteration, the νOH/νOD wavenumber ratios show values between 1.18 and 1.25, confirming the strong bonding that leads to an (H₅O₂⁺, 2 H₂O) n water layer between the [Fe 3 (PO 4 ) 2 ] n sheets, as well as the high proton mobility. Consequently, the chemical formula of the compound should rather be Fe 2.5 (PO 4 ) 2 H 5 O 2 ⋅2⋅H 2 O. An Fe 3 III O(HPO₄) 2 ⋅nH₂O form is obtained by immersion in molten ammonium nitrate.
Ludlamite, like its lamellar counterparts HUP, HUAS, and HFeS, is a reasonably good proton conductor with a thermal stability up to ≈ 150 • C.
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BibTeX
@article{colomban2026protonated,
title = {{Protonated water layer in Ludlamite lamellar iron phosphate (Fe3(PO4)2·4H2O)}},
author = {Philippe Colomban and Ricardo Scholz and Roberto L Moreira},
journal = {Journal of Molecular Structure},
year = {2026},
month = oct,
doi = {10.1016/j.molstruc.2026.147932},
url = {https://hal.science/hal-05844230v1},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Protonated water layer in Ludlamite lamellar iron phosphate (Fe3(PO4)2·4H2O)
AU - Philippe Colomban
AU - Ricardo Scholz
AU - Roberto L Moreira
PY - 2026
DA - 2026/10/30
JO - Journal of Molecular Structure
DO - 10.1016/j.molstruc.2026.147932
UR - https://hal.science/hal-05844230v1
AB - The vibrational signature (Raman and IR) of natural ludlamite single crystals is discussed, along with the evolution of the Raman spectrum after heating to 90, 150, and 200 • C. The observation of broad "ABC" bands in the stretching mode region-characteristic of a strong, symmetric hydrogen bond-indicates the formation of H 2 O-H + -OH 2 (or H 5 O 2 + ) species. After deuteration, the νOH/νOD wavenumber ratios show values between 1.18 and 1.25, confirming the strong bonding that leads to an (H₅O₂⁺, 2 H₂O) n water layer between the [Fe 3 (PO 4 ) 2 ] n sheets, as well as the high proton mobility. Consequently, the chemical formula of the compound should rather be Fe 2.5 (PO 4 ) 2 H 5 O 2 ⋅2⋅H 2 O. An Fe 3 III O(HPO₄) 2 ⋅nH₂O form is obtained by immersion in molten ammonium nitrate. Ludlamite, like its lamellar counterparts HUP, HUAS, and HFeS, is a reasonably good proton conductor with a thermal stability up to ≈ 150 • C.
SN - 0022-2860
SN - 0022-2860
ER -