Transition to a crystalline high-pressure phase in a-GeO2 at room temperature

alpha-quartz-type GeO2 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 GeO2 was found to be monoclinic, space group P2(1) / c, Z = 6 and is built up of 3 X 2 kinked chains of edge-sharing GeO6 octahedra. This phase is 45% denser than alpha-quartz-type GeO2 and 1% less dense than the rutile-type phase and is metastable from ambient pressure up to at least 50 GPa at roam temperature. Upon heating this monoclinic phase at pressures up to 22 GPa, rutile-type GeO2 is formed, whereas at 43 GPa a mixture of the CaCl2-type and Fe2N-rype phases is obtained.