Ge coordination states in SiO2-GeO2 glasses at high pressure, inferred from in situ XAFS at the Ge K-edge

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In SiO2-GeO2 glasses submitted to high pressure conditions, germanium atoms undergo a coordination change from four to six on a pressure-range depending on the composition. In the transition region, the possibility of having a mixture of tetrahedra and octahedra for Ge instead of the intermediate fivefold coordination state has been studied. Through comparison of the informations extracted from XANES and EXAFS, the model of a mixture of IV and VI coordination states, with a possible small amount of fivefold coordinated Ge appearing on the compression, is favoured.