Polyamorphism of GeO ₂ Glass at High Pressure

Polyamorphism of network‐forming SiO 2 and GeO 2 glasses at high pressures is a puzzling topic in condensed matter physics and has long‐standing interest because of their important geophysical and geochemical implications. Molecular dynamics simulations suggest that there are multiple amorphous–amorphous transitions at high pressure with parallel high‐pressure crystalline counterparts. However, it is very challenging to experimentally distinguish the pressure‐induced subtle change in the amorphous state at high pressure. Recently, a high‐pressure X‐ray absorption fine structure (HP‐XAFS) method is developed using a diamond anvil cell (DAC) to measure the local structure of polyamorphs in GeO 2 glass at high pressure. The results indicate that GeO 2 glass shows multiple polyamorphs at high pressure with a local structure, in general, similar to their high‐pressure crystalline states in the first coordination shell but with increasing differences in the distant coordination shells. Three pressure‐induced polyamorphs in GeO 2 glass are recognized unambiguously at high pressure, i.e., α‐quartz‐like, rutile‐like, and pyrite‐like amorphous structures. The obtained knowledge of these polyamorphs is helpful for understanding the mechanisms of network compression behavior and physical properties of SiO 2 and GeO 2 glasses and melts under extreme conditions.