Pressure-induced coordination changes in crystalline and vitreousGeO2

In situ high-pressure x-ray-absorption spectra have been performed on amorphous and crystalline ${\mathrm{GeO}}_2$ using a diamond-anvil cell adapted to ane energy-dispersive spectrometer. The coordination of Ge changes from fourfold to sixfold at pressures between 7 and 9 GPa. The progressive evolution of the measured Ge-O distances as well as the modification in the x-ray-absorption near-edge structure indicate two different sites rather than a progressive site modification. The phase transition observed in the amorphous phase is reversible in contrast to that observed in the crystalline form.