Structural changes in amorphous GeS2 at high pressure

High-pressure modifications in glassy GeS2 have been investigated up to 45 GPa using the diamond anvil cell through x-ray absorption fine structure (XAFS) spectroscopy and x-ray diffraction (XRD). The gradual increase in the Ge-S distance of about 0.1 Å between 15 and 25 GPa evidenced by XAFS is interpreted as a signature of a coordination increase around Ge. The negative shift of the germanium K absorption edge position is connected to the progressive metallization of the glass. XRD measurements reveal the amorphous-amorphous nature of the structural transformation. The first sharp diffraction peak loses intensity and shifts toward higher Q values in the first few gigapascal, reflecting changes in the intermediate-range order prior to the local coordination increase. The observed changes are reversible after pressure release with strong hysteresis.