Pressure-induced Ge coordination change and polyamorphism in SiO2–GeO2 glasses

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The pressure-induced coordination change of Ge from fourfold to sixfold coordination state has been studied by in situ high pressure X-ray Absorption Spectroscopy at Ge K-edge, in SiO2–GeO2 tetrahedral framework glasses. The transformation occurs at higher pressure and over a broader pressure range when the SiO2 content increases. A careful analysis of both XANES and EXAFS signals supports a model of a mixing of [4]Ge and [6]Ge states in the transition region, in agreement with a kinetically hindered first-order process for the transformation at room temperature.