High-pressure phase transformations in vitreous and crystalline GeO2 (rutile)

Phase transformations in vitreous and crystalline GeO₂ (rutile) have been investigated up to ～50 GPa and ～1000°C by using a diamond anvil pressure cell coupled with a YAG laser heating system and in situ x-ray diffraction techniques. The results show that whereas the vitreous GeO₂ transforms into a hexagonal phase at pressures ～25 GPa, the crystalline GeO₂ transforms into an orthorhombic phase at ～28 GPa; the molar volume changes for the hexagonal and orthorhombic transformations are ? 1.0% (at 25 GPa) and ? 3.0% (at 28 GPa), respectively. When unloaded to 0.1 MPa, both the hexagonal and orthorhombic phases of GeO₂ are retained, and the zero-pressure molar volume is 0.7% larger and 4.5% smaller than that of the rutile-structured GeO₂, respectively. These results are in good agreement with previously published data.