A vibrational study of phase transitions in Fe2P2O7 and Cr2P2O7 under high-pressures

Nicolas A. Blanc, Quentin Williams, Brahim El Bali, Rachid Essehli

Research output: Contribution to journalArticle

Abstract

The vibrational properties of synthetic iron diphosphate (Fe2P2O7) and chromium diphosphate (Cr2P2O7) are studied under high-pressure conditions between ~22 and ~30 GPa, respectively. Each compound's structural response to pressure and pressure-induced phase transitions are characterized. The chromium-bearing sample shows coalescence of infrared bands occurring near 6 and 17 GPa: these may be associated with increases in the local symmetry of the P2O7 group. The iron sample undergoes a first-order phase transition near ~9 GPa, and a possible phase transition near 5.5 GPa. At 9 GPa, the initially single, strong symmetric PO4 stretching mode splits into four modes, and the sole asymmetric PO4 stretching mode splits into two bands. These changes indicate the presence of multiple tetrahedral environments within a larger volume unit cell, and the relative frequencies of the split vibrations indicate a P2O7 environment with a markedly narrowed P-O-P angle. The difference between the behavior of the iron and chromium compounds is probably generated by the smaller iron ion producing a discontinuous decrease in the P-O-P angle at lower pressures than in the analogous chromium compound. Our results demonstrate that the dimerized P2O7 group remains stable under compression to over 20-30 GPa at 300 K.

Original languageEnglish
JournalJournal of the American Ceramic Society
DOIs
Publication statusAccepted/In press - 1 Jan 2018

Fingerprint

phase transition
chromium
Chromium Compounds
Phase transitions
Chromium compounds
iron
Iron
Diphosphates
Chromium
Stretching
Bearings (structural)
Iron Compounds
Iron compounds
structural response
coalescence
Coalescence
symmetry
low pressure
vibration
compression

Keywords

  • CrPO
  • Diphosphates
  • FePO
  • Infrared spectroscopy
  • Pressure
  • Raman spectroscopy

ASJC Scopus subject areas

  • Ceramics and Composites
  • Geology
  • Geochemistry and Petrology
  • Materials Chemistry

Cite this

A vibrational study of phase transitions in Fe2P2O7 and Cr2P2O7 under high-pressures. / Blanc, Nicolas A.; Williams, Quentin; El Bali, Brahim; Essehli, Rachid.

In: Journal of the American Ceramic Society, 01.01.2018.

Research output: Contribution to journalArticle

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AB - The vibrational properties of synthetic iron diphosphate (Fe2P2O7) and chromium diphosphate (Cr2P2O7) are studied under high-pressure conditions between ~22 and ~30 GPa, respectively. Each compound's structural response to pressure and pressure-induced phase transitions are characterized. The chromium-bearing sample shows coalescence of infrared bands occurring near 6 and 17 GPa: these may be associated with increases in the local symmetry of the P2O7 group. The iron sample undergoes a first-order phase transition near ~9 GPa, and a possible phase transition near 5.5 GPa. At 9 GPa, the initially single, strong symmetric PO4 stretching mode splits into four modes, and the sole asymmetric PO4 stretching mode splits into two bands. These changes indicate the presence of multiple tetrahedral environments within a larger volume unit cell, and the relative frequencies of the split vibrations indicate a P2O7 environment with a markedly narrowed P-O-P angle. The difference between the behavior of the iron and chromium compounds is probably generated by the smaller iron ion producing a discontinuous decrease in the P-O-P angle at lower pressures than in the analogous chromium compound. Our results demonstrate that the dimerized P2O7 group remains stable under compression to over 20-30 GPa at 300 K.

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