Coordination and RedOx ratio of iron in sodium‐silicate glasses

Diluted Fe 3+ in silicate glasses: Structural effects of Fe-redox state and matrix composition. An optical absorption and X-band/Q-band EPR study

“…According to previous articles that studied the effect of total Fe-content in sodium-silicate glasses, the reduced samples investigated here have a g = 2 signal shape similar to the one observed at higher iron content ([Fe 2 O 3 ] > 1 mol%). [17,18] In these high Fe-glasses, Fe 3+ -rich clusters have been shown by optical absorption and Mössbauer spectroscopic properties [49] and confirmed by neutron diffraction and numerical simulations. [50] The present study shows that, in reduced samples, residual Fe 3+ tends to segregate, with an EPR signature similar to that in concentrated glasses.…”

“…[14][15][16] The attribution of the feature at g = 2 is less clear. [17] Different scenarios have been proposed: (i) a signal due to exchange-coupled pairs or clusters of more than two atoms [18] involving edge-or face-sharing Fe 3+ sites [16,19,20]. These clusters could be trimers [21] up to nano-clusters as in ferritine [22], nanoparticles [23] or obsidian wt.% glasses [7,24]; (ii) a paramagnetic signal due to Fe 3+ in axially distorted sites (E/D ~ 0) [19], this signal being enhanced by dipole-dipole interactions.…”

Structure and glass transition temperature of sodium-silicate glasses doped with iron

“…Non-monotonic behavior T g vs. Fe content can be explained with the results of structural investigations. The environment of Fe(III) in soda-silica glasses doped with iron were detail studied by Dunaeva et al [23,30]. As the results of Mössbauer spectroscopy, EPR and XANES/EXAFS, it was shown that in the glasses with low iron content (under 4 wt.% Fe 2 O 3 ) CN N 4, moreover, in the region under 1 wt.% Fe 2 O 3 isolated Fe(III) predominate over clustered, in the area between 1 and 4 wt.% their quantities are comparable.…”

“…This method is analogous to one described in [23], so we believe that compositions of glasses correspond to the initial raw batch. The mixtures were prepared from analytically pure materials.…”

“…The vertical and horizontal error bars represent the uncertainties of the peak area determination and iron content, correspondingly. The maximal standard deviation for iron quantities was estimated from the results of EDX analysis for identical glasses [23].…”