Spectroscopic and Structural Properties of Iron in Silicate Glasses

Abstract : Among the infinite possibilities of glass compositions, soda-lime silicates represent of 90% of the glass production and are widely used for many industrial applications (e.g. automotive, solar panels, construction). Specific glasses silicate containing 0.5 wt% of Fe2O3 were synthesized with extreme redox. The use of reducing and oxidizing conditions allows to isolate the respective Fe2+ and Fe3+ spectroscopic signatures that are usually mixed due to the heterovalent nature of iron. However, synthesis conditions do not allow to isolate specific iron environment that remains distributed in glasses. Thus, Fe2+- and Fe3+-bearing minerals containing iron in well defined environments were selected. The comprehension of structure-spectroscopy relationships in these crystalline references is a preliminary step to the interpretation of iron spectroscopic signature in glasses. A multi-spectroscopic study was performed on glasses and minerals by combining experi- mental (optical absorption, X-ray absorption at the iron K edge, and electron paramagnetic resonance) and theoretical (multielectronic calculations using ligand field multiplet approach to reproduce the K pre-edge and optical absorption spectra) methods. The study of crystalline references evidenced the influence of local symmetry (Oh, Td, D4h/C4v et D3h/C3v) on iron sites and of p–d hybridization on iron spectroscopic signatures. Concerning the study of reduced silicate glasses, the majority of Fe2+ is present in 5- fold coordination, this speciation can reproduce and explain the iron signature by using a distribution of the crystal field parameters to take into account the amorphous nature of glass. The analysis of oxidized glasses supports the existence of Fe3+ in 5-fold coordination. These species need to be considered, in addition to tetrahedral geometries, for the interpretation of optical spectra. This study shed light on structural and spectroscopic variations of iron due to the substitution of calcium by magnesium or by the absence of alkali in the composition of the glass matrix.
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Vincent Vercamer. Spectroscopic and Structural Properties of Iron in Silicate Glasses. Material chemistry. Université Pierre et Marie Curie - Paris VI, 2016. English. ⟨NNT : 2016PA066077⟩. ⟨tel-01458771⟩

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