Structure refinement of GeO₂ polymorphs at high pressures and temperatures by energy-dispersive spectra of powder diffraction

Profile fitting of energy-dispersive (ED) X-ray diffraction spectra of GeO₂ polymorphs, hexagonal (P3₂21, Z = 3) and tetragonal (P4₂/mmm, Z = 2), was examined under high-pressure and high-temperature conditions. These ED spectra were observed with a diamond-anvil cell on a synchrotron-radiation source. Structure refinement of hexagonal GeO₂ at several pressures was made, in which diffraction intensities were corrected for the energy spectrum of the incident radiation, escape efficiency of the detector, background scattering and absorption. It was confirmed that the Ge-O distances in hexagonal GeO₂ vary little with pressure, whereas the mean O-O distance and volume of the GeO₄ tetrahedron decrease linearly with pressure. The decrease in the Ge-O-Ge linking angle between tetrahedra causes the deformation of the framework composed of corner-linked tetrahedra, which is mainly responsible for the bulk volume compression. The bulk modulus of the two polymorphs has been calculated on the basis of the volumetric compressibility up to 10 GPa.