Transition to a crystalline high-pressure phase inα−GeO2at room temperature

Abstract

α-quartz-type ${\mathrm{GeO}}_2$ was found to undergo a transition to a crystalline phase above 6 GPa at room temperature from in situ, angle-dispersive, x-ray-diffraction measurements. There was no evidence of amorphization, although this phase is poorly crystallized. Hydrostatic conditions play an important role in the crystallization process. The crystal structure of this high-pressure form of ${\mathrm{GeO}}_2$ was found to be monoclinic, space group ${P2\mathrm{}}_1/c,$ $Z=6\mathrm{}$ and is built up of $3\times 2$ kinked chains of edge-sharing ${\mathrm{GeO}}_6$ octahedra. This phase is 45% denser than α-quartz-type ${\mathrm{GeO}}_2$ and 1% less dense than the rutile-type phase and is metastable from ambient pressure up to at least 50 GPa at room temperature. Upon heating this monoclinic phase at pressures up to 22 GPa, rutile-type ${\mathrm{GeO}}_2$ is formed, whereas at 43 GPa a mixture of the ${\mathrm{CaCl}}_2$-type and ${\mathrm{Fe}}_2\mathrm{N}$-type phases is obtained.