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Transition to a crystalline high-pressure phase in α − GeO 2 at room temperature

2000; American Physical Society; Volume: 61; Issue: 13 Linguagem: Inglês

10.1103/physrevb.61.8701

1095-3795

Julien Haines, Jean‐Michel Léger, C. Chateau,

Glass properties and applications

\ensuremath{\alpha}-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 ${P2}_{1}/c,$ $Z=6$ and is built up of $3\ifmmode\times\else\texttimes\fi{}2$ kinked chains of edge-sharing ${\mathrm{GeO}}_{6}$ octahedra. This phase is 45% denser than \ensuremath{\alpha}-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.