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Structural and spectroscopic properties of calcium-iron Ca9Fe(PO4)7phosphate

Authors
Journal
Materials Research Bulletin
0025-5408
Publisher
Elsevier
Publication Date
Volume
35
Issue
12
Identifiers
DOI: 10.1016/s0025-5408(00)00403-7
Keywords
  • A. Inorganic Compounds
  • C. Mössbauer Spectroscopy
  • D. Electronic Paramagnetic Resonance (Epr)

Abstract

Abstract Fresh (f-) and reduced (r-) Ca 9Fe(PO 4) 7 whitlockite-like compounds were prepared and characterized by X-ray diffraction (XRD), IR, temperature programmed reduction and oxidation (TPR/TPO), UV-visible, electron paramagnetic resonance (EPR), and 57Fe Mössbauer spectroscopy. TPR/TPO, XRD, and IR investigations showed that cycles of reduction and oxidation reversibly affected the iron cations without noticeable modification of the structure. The reduction by H 2 was accompanied by a protonation of the sample and a slight increase of the unit-cell parameters. It was observed that the reduction of Fe 3+ to Fe 2+ never exceeded 91%. The simulation of f-Ca 9Fe(PO 4) 7 EPR spectra and the Mössbauer investigations confirmed that the Fe 3+ cations are located in highly symmetrical sites. These techniques also revealed that in r-Ca 9Fe(PO 4) 7 the residual ferric ions are in a rhombic symmetry and the Fe 2+ ions are in octahedral sites slightly distorted by the Jahn-Teller effect.

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