Infrared spectroscopic properties of goethite: anharmonic broadening, long-range electrostatic effects and Al substitution

Marc Blanchard*, Etienne Balan, Paola Giura, Keevin Beneut, Haohao Yi, Guillaume Morin, Carlos Pinilla, Michele Lazzeri, Andrea Floris

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

The infrared spectrum and its temperature dependence (20-320 K) were collected on a synthetic goethite sample (alpha-FeOOH). In addition, the infrared powder absorption spectrum of goethite and aluminum-substituted goethite was computed using ab initio quantum mechanical calculations based on density functional theory. This combined experimental and theoretical approach allows (1) the unequivocal assignment of absorption bands to the corresponding vibrational modes, (2) separate identification of the effects of the particle shape and of the aluminum substitution on the infrared spectrum, and (3) a discussion of the anharmonic properties and the origin of the line broadening in goethite. In particular, the two well-resolved OH bending absorption bands show different temperature evolution. Their detailed analysis suggests that the broadening of the band at similar to 800 cm(-1) cannot be described solely by a usual three-phonon process. The strong anharmonic behavior of this mode implies the addition of a four-phonon process, such as a pure dephasing process. In our calculations, the effect of the Hubbard U correction is also investigated and found to be most visible on the OH stretching and bending modes, in relation to the associated structural relaxation. The OH stretching frequencies decrease, leading to a better agreement with experimental frequencies, while the OH bending frequencies increase.

Original languageEnglish
Pages (from-to)289-302
Number of pages14
JournalPHYSICS AND CHEMISTRY OF MINERALS
Volume41
Issue number4
DOIs
Publication statusPublished - Apr 2014

Keywords

  • Goethite
  • Aluminum substitution
  • Density functional theory
  • Infrared spectroscopy
  • OH STRETCHING MODES
  • ALPHA-FEOOH
  • X-RAY
  • IRON-OXIDES
  • ALUMINUM SUBSTITUTION
  • VARYING CRYSTALLINITY
  • RAMAN-SPECTROSCOPY
  • MOSSBAUER-SPECTRA
  • AB-INITIO
  • IN-SITU

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