An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of a-quartz, SiO2) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112 eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe2? is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell: \Fe–O[= 1.78(2) A ° , the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe3? variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4? or 3?. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe4? is stabilised by the favourable local structural arrangement.

A Fe K-edge XAS study of amethyst / F. Di Benedetto; • F. D’Acapito; • G. Fornaciai; •M. Innocenti; • G. Montegrossi; • L. A. Pardi; •S. Tesi; • M. Romanelli. - In: PHYSICS AND CHEMISTRY OF MINERALS. - ISSN 0342-1791. - STAMPA. - 37:(2010), pp. 283-289. [10.1007/s00269-009-0332-0]

A Fe K-edge XAS study of amethyst

DI BENEDETTO, FRANCESCO;INNOCENTI, MASSIMO;ROMANELLI, MAURIZIO
2010

Abstract

An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of a-quartz, SiO2) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112 eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe2? is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell: \Fe–O[= 1.78(2) A ° , the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe3? variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4? or 3?. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe4? is stabilised by the favourable local structural arrangement.
2010
37
283
289
F. Di Benedetto; • F. D’Acapito; • G. Fornaciai; •M. Innocenti; • G. Montegrossi; • L. A. Pardi; •S. Tesi; • M. Romanelli...espandi
File in questo prodotto:
File Dimensione Formato  
Innocenti 69.pdf

Accesso chiuso

Tipologia: Versione finale referata (Postprint, Accepted manuscript)
Licenza: Tutti i diritti riservati
Dimensione 296.52 kB
Formato Adobe PDF
296.52 kB Adobe PDF   Richiedi una copia

I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/393346
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 35
  • ???jsp.display-item.citation.isi??? 29
social impact