Medium-range structure modifications induced by Fe3+/Fetot. in volcanic glasses: a low-frequency Raman spectroscopy study

Abstract

Here is carried out a Raman scattering study on the boson peak evolution of an iron-rich peralkaline rhyolite in function of both the iron oxidation state and the glass transition temperature. It is reported here that the distribution of low-frequency modes in the boson peak range is only slightly affected for an iron ratio (Fe3+/Fetot.) from 0.83 down to 0.24. Their distribution does not change in the boson peak range as a function of Fe3+/Fetot., until the reduction process starts to modify the glass network from a dominantly fourfold coordinated Fe3+ structures into a structure mostly governed by fivefold coordinated Fe2+. This trend is also related to a decreasing glass transition temperature peak, mirroring an increasing proportion of weakest bonds with respect to the stronger ones.