Structural changes in vitreous GeSe ₄ under pressure

High-energy X-ray diffraction experiments have been performed on GeSe ₄ glass up to pressures of 8.6 GPa, and the equation of state has been measured up to 10 GPa. The X-ray structure factors reveal a decrease in the first sharp diffraction peak intensity and broadening with pressure, which signifies a break-up of the intermediate range order in the glass. In contrast, the principal peak in the structure factor shows an increase in intensity and a sharpening with pressure, which is attributed to an increase in extended range order and coherence of the compacted units. The average nearest neighbor coordination number is found to remain constant in GeSe ₄ glass (within experimental error) over the pressure range measured. This is in contrast with the gradual increase found in GeSe ₂ glass. Rather, in GeSe ₄ glass the densification mechanism is shown to be associated with large inward shifts of the second neighbor and higher coordination shells. These features appear as additional correlations at 3.3 and 5.3 Å in the differences taken between adjacent pair distribution functions with increasing pressure.