EXAFS investigations on the pressure induced local structural changes of GeSe₂ glass under different hydrostatic conditions

Abstract

Pressure-induced transformations in glassy GeSe2 have been studied using the x-ray absorption spectroscopy. Experiments have been carried out at the scanning-energy beamline BM23 (ESRF) providing a micrometric x-ray focal spot up to pressures of about 45 GPa in a diamond anvil cell. Both Se and Ge K-edge experiments were performed under different hydrostatic conditions identifying the metalization onsets by accurate determinations of the edge shifts. The semiconductor-metal transition was observed to be completed around 20 GPa when neon was used as a pressure transmitting medium, while this transition was slightly shifted to lower pressures when no pressure transmitting medium was used. Accurate double-edge EXAFS (Extended X-ray Absorption Fine Structure) refinements were carried out using advanced data-analysis methods. EXAFS data-analysis confirmed the trend shown by the edge shifts for this disordered material, showing that the transition from tetrahedral to octahedral coordination for Ge sites is not fully achieved at 45 GPa. Results of present high pressure EXAFS experiments have shown the absence of significant neon
incorporation into the glass within the pressure range up to 45 GPa.