Pressure dependence of the first sharp diffraction peak in chalcogenide and oxide glasses

X-ray diffraction patterns of GeS2 and GeO2, glasses under pressure up to 100 kbar have been measured in order to examine their medium-range structure. Qualitative differences have been found between the pressure dependences of the first sharp diffraction peaks, suggesting distinct glassy structures. The first peak in chalcogenide glasses can be ascribed to inter-layer correlations, which become degraded at high pressures.