Al—Si ordering in albite: A combined single‐crystal X‐ray diffraction and Raman spectroscopy study. (9th October 2018)

• Record Type: Journal Article
• Authors: Tribaudino, Mario; Gatta, G. Diego; Aliatis, Irene; Bersani, Danilo; Lottici, Pier Paolo
• Is Part Of: Journal of Raman spectroscopy. Volume 49:Number 12(2018)
• Page Start: 2028
• Page End: 2035
• Publication Date: 2018-10-09
• Subjects: Al—Si order -- high‐temperature annealing -- plagioclase -- X‐ray diffraction; Raman spectroscopy -- Periodicals; 535.846
• DOI: 10.1002/jrs.5490
• Languages: English
• ISSNs: 0377-0486

Abstract

Abstract: Raman spectra of a low albite single crystal were collected during annealing at 1076°C for up to 46 days. At seven annealing stages, the single crystal structure was refined by X‐ray intensity data to determine the degree of Al—Si order using the tetrahedral bond distances. Single‐crystal X‐ray diffraction showed that residuals in the difference‐Fourier map of the electron density and atomic displacement parameters of Si, O, and, most, Na, increase with Al—Si disorder. The Raman spectra show a significant broadening with disorder, and some slight peak shift. Three strong peaks, at 290 cm −1 ( ν c ), 478 cm −1 ( ν b ), and 507 cm −1 ( ν a ) in ordered albite, were examined in further detail. ν c and ν b show a red‐shift with broadening and Al—Si disorder; ν a blue‐shifts with disorder and shows only a minor broadening. The broadening and shifts in Raman spectra are caused by structural deformation associated with Al—Si disorder. The ν a peak at 507 cm −1 is the least affected by Al—Si disorder and is suitable to assess compositional changes in plagioclase. The Al—Si order can be determined in albite by the wavenumber difference Δab between the two main peaks ν a and ν b as follows: Q od 2 = 9.50 75 − 0.307 25 Δ ab, R 2 = 0.94, where Q od is an order parameter derived from average tetrahedral Al—O and Si—O bond distances. Abstract : Raman spectra of a low albite single crystal were collected during annealing at 1076°C up to 42 days. At seven annealing stages, the single crystal structure was refined (by X‐ray intensity data) in order to calibrate the degree of Al—Si order with peak position and linewidth.The Raman spectra show a significant broadening with disorder, and some slight peak shift. Different peaks show different response to Al—Si disorder.