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Title: Multi-spectroscopic study of Fe(II) in silicate glasses:Implications for the coordination environment of Fe(II) in silicatemelts

Abstract

The coordination environment of Fe(II) has been examined inseven anhydrous ferrosilicate glasses at 298 K and 1 bar using 57FeMossbauer, Fe K-edge X-ray near edge structure (XANES), and extendedX-ray absorption fine structure (EXAFS), UV-Vis-NIR, and magneticcircular dichroism (MCD) spectroscopies. Glasses of the followingcompositions were synthesized from oxide melts (abbreviation andnonbridging oxygen:tetrahedral cation ratio (NBO/T) in parentheses):Li2FeSi3O8 (LI2: 1.33), Rb2FeSi3O8 (RB2: 1.33), Nal.08Fel.l7Si3.l3O8(NAl: 1.09), Nal.46Ca0.24Fel.08Si2.97O8 (NC6: 1.38),Nal.09Ca0.51Fe0.72Si3.10O8 (NC2: 1.15), Na0.99Ca0.92Fe0.24 Si3.17O8 (NCl:1.04), and Na0.29Mg0.53Ca0.52Fe0.56Al0.91Si2.44O8 (BAS: 1.05). Mossbauer,XANES, and EXAFS information suggest s that iron is dominantly ferrous inall glasses (<10 atom percent Fe(III)) with an average first-neighborFe(II) coordination varying from 4 to 5.2 (\2610.2) oxygens. TheUV-Vis-NIR spectrum of each sample exhibits intense absorption centerednear 8100-9200 cm-1 and weak absorption near 5000 cm-l, which cannot beassigned unambiguously. The MCD spectrum of NC6 glass, which is the firstsuch measurement on a silicate glass, shows three transitions at 8500cm-1, 6700 cm-1, and 4500 cm-1. Thebehavior of these MCD bands as afunction of temperature (1.6 K to 300 K) and magnetic field strength (1 Tto 7 T) indicates that they most likely arise from three distinct Fe(II)sites with different ground states, two of which are 5-coordinated andone of which is 4-coordinated by oxygens. The combinedmore » results suggestthat Fe(II) predominantly occupies 5- and 4-coordinated sites in eachglass, with the ratios differing for the different compositions. Smallamounts of 6-coordinated Fe(II) are possible as well, but primarily inthe more basic glass compositions such as BAS. The substitution of Li(I)for Rb(I) in the M2FeSi3O8 base glass composition causes a weakening ofthe average Fe(II)-O bond, as indicated by the longer Fe(II)-O distancein the latter. The basalt composition glass was found to have the largestFe(II) sites relative to those in the other glasses in this study. A bondvalence model that helps predict the coordination number of Fe(II) insilicate glasses is proposed. The structural information extrapolated toFe(II)-bearing melts is parameterized using bond valence theory, whichhelps to rationalize the melt-crystal partitioning behavior of ferrousiron in natural and synthetic melt-crystal systems.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
COLLABORATION - StanfordU.
OSTI Identifier:
901238
Report Number(s):
LBNL-60925
Journal ID: ISSN 0016-7037; GCACAK; TRN: US200713%%210
DOE Contract Number:  
DE-AC02-05CH11231
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 69; Journal Issue: 17; Related Information: Journal Publication Date: 09/2005; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ABSORPTION; ATOMS; BASALT; CATIONS; COORDINATION NUMBER; FINE STRUCTURE; GLASS; GROUND STATES; IRON; MAGNETIC CIRCULAR DICHROISM; MAGNETIC FIELDS; OXIDES; SILICATES; VALENCE

Citation Formats

Jackson, W E, Farges, F, Yeager, M, Mabrouk, P, Rossano, S, Waychunas, G, Solomon, E, and Brown, Jr, Gordon E. Multi-spectroscopic study of Fe(II) in silicate glasses:Implications for the coordination environment of Fe(II) in silicatemelts. United States: N. p., 2003. Web.
Jackson, W E, Farges, F, Yeager, M, Mabrouk, P, Rossano, S, Waychunas, G, Solomon, E, & Brown, Jr, Gordon E. Multi-spectroscopic study of Fe(II) in silicate glasses:Implications for the coordination environment of Fe(II) in silicatemelts. United States.
Jackson, W E, Farges, F, Yeager, M, Mabrouk, P, Rossano, S, Waychunas, G, Solomon, E, and Brown, Jr, Gordon E. Fri . "Multi-spectroscopic study of Fe(II) in silicate glasses:Implications for the coordination environment of Fe(II) in silicatemelts". United States.
@article{osti_901238,
title = {Multi-spectroscopic study of Fe(II) in silicate glasses:Implications for the coordination environment of Fe(II) in silicatemelts},
author = {Jackson, W E and Farges, F and Yeager, M and Mabrouk, P and Rossano, S and Waychunas, G and Solomon, E and Brown, Jr, Gordon E},
abstractNote = {The coordination environment of Fe(II) has been examined inseven anhydrous ferrosilicate glasses at 298 K and 1 bar using 57FeMossbauer, Fe K-edge X-ray near edge structure (XANES), and extendedX-ray absorption fine structure (EXAFS), UV-Vis-NIR, and magneticcircular dichroism (MCD) spectroscopies. Glasses of the followingcompositions were synthesized from oxide melts (abbreviation andnonbridging oxygen:tetrahedral cation ratio (NBO/T) in parentheses):Li2FeSi3O8 (LI2: 1.33), Rb2FeSi3O8 (RB2: 1.33), Nal.08Fel.l7Si3.l3O8(NAl: 1.09), Nal.46Ca0.24Fel.08Si2.97O8 (NC6: 1.38),Nal.09Ca0.51Fe0.72Si3.10O8 (NC2: 1.15), Na0.99Ca0.92Fe0.24 Si3.17O8 (NCl:1.04), and Na0.29Mg0.53Ca0.52Fe0.56Al0.91Si2.44O8 (BAS: 1.05). Mossbauer,XANES, and EXAFS information suggest s that iron is dominantly ferrous inall glasses (<10 atom percent Fe(III)) with an average first-neighborFe(II) coordination varying from 4 to 5.2 (\2610.2) oxygens. TheUV-Vis-NIR spectrum of each sample exhibits intense absorption centerednear 8100-9200 cm-1 and weak absorption near 5000 cm-l, which cannot beassigned unambiguously. The MCD spectrum of NC6 glass, which is the firstsuch measurement on a silicate glass, shows three transitions at 8500cm-1, 6700 cm-1, and 4500 cm-1. Thebehavior of these MCD bands as afunction of temperature (1.6 K to 300 K) and magnetic field strength (1 Tto 7 T) indicates that they most likely arise from three distinct Fe(II)sites with different ground states, two of which are 5-coordinated andone of which is 4-coordinated by oxygens. The combined results suggestthat Fe(II) predominantly occupies 5- and 4-coordinated sites in eachglass, with the ratios differing for the different compositions. Smallamounts of 6-coordinated Fe(II) are possible as well, but primarily inthe more basic glass compositions such as BAS. The substitution of Li(I)for Rb(I) in the M2FeSi3O8 base glass composition causes a weakening ofthe average Fe(II)-O bond, as indicated by the longer Fe(II)-O distancein the latter. The basalt composition glass was found to have the largestFe(II) sites relative to those in the other glasses in this study. A bondvalence model that helps predict the coordination number of Fe(II) insilicate glasses is proposed. The structural information extrapolated toFe(II)-bearing melts is parameterized using bond valence theory, whichhelps to rationalize the melt-crystal partitioning behavior of ferrousiron in natural and synthetic melt-crystal systems.},
doi = {},
journal = {Geochimica et Cosmochimica Acta},
issn = {0016-7037},
number = 17,
volume = 69,
place = {United States},
year = {2003},
month = {7}
}