The compression behavior of crystalline and amorphous germania holds considerable interest as an analog for silica and for understanding the structural response of AX2 compounds generally. In this paper, the α-PbO2-type and Pa3-type polymorphs of GeO2 were investigated under high pressure using angle-dispersive synchrotron x-ray diffraction in the laser-heated diamond anvil cell. Theoretical calculations based on density functional theory were also performed. The experimental pressure-volume data were fitted to third-order Birch-Murnaghan equations of state. The fit parameters for the α-PbO2 type are V0=53.8(2)Å3,K0T=293(7)GPa with fixed K0T′=4, where V,KT, and KT′ are the volume, isothermal bulk modulus, and pressure derivative of the bulk modulus and the subscript zero refers to ambient conditions. The corresponding parameters for the Pa3-type phase are V0=50.3(3)Å3,K0T=342(12)GPa with fixed K0T′=4. The theoretical calculations are in good agreement with the experimental results with slight underestimation and overestimation of V0 and K0T, respectively. A theoretical Hugoniot was calculated from our data and compared to shock equation of state data for vitreous and rutile-type GeO2. The high-pressure phase observed on the Hugoniot is most consistent with either the α-PbO2-type or CaCl2-type phase. Finally, we have compared our data on crystalline germania with existing studies on the corresponding phases of SiO2 to better understand the effects of cation substitution on phase transformations and equations of state in group 14 dioxides.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics