Pressure-induced coordination changes in crystalline and vitreous<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">GeO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

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.