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

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 Ge-[4] and Ge-[6] states in the transition region, in agreement with a kinetically hindered first-order process for the transformation at room temperature. (C) 2004 Elsevier B.V. All rights reserved.