High-pressure form of pyrite-type germanium dioxide

Structural phase transitions of germanium dioxide (GeO₂) have been investigated at pressures up to 120 GPa, which was heated to a temperature above 2000 K, using a laser-heated diamond anvil cell technique. A phase transition between CaCl₂-type and α-PbO₂-type phases was observed at about 50 GPa. At pressures higher than 90 GPa, we also observed the occurrence of a new high-pressure phase of pyrite-type (modified-fluorite type) structure (Pa3) that is denser than other known GeO₂ phases. Our results were consistent with the high-pressure transition sequence of tin dioxide (SnO₂) as analog of GeO₂. The new structure of the GeO₂ high-pressure phase may be that of high-pressure silica (SiO₂) phase predicted by the theoretical investigations.