Higher than 6-fold Ge-O coordination transition in glassy GeO2 beyond 160 GPa and simultaneous cryogenic temperature conditions

We aim to unambiguously clarify the compression mechanism of glassy GeO2 beyond 150 GPa and more specifically to study the occurrence of a higher Ge coordination than 6-fold, which remains highly debated. The controversies are mostly due to the experimental difficulties to probe the structure of an amorphous micrometric sample at such conditions. In our previous HP XAS experiment (report HC-4435) we could acquire unprecedented high-quality EXAFS data of glassy GeO2 up to 160 GPa that permitted us to clearly discriminate its compaction mechanism. However at 163 GPa glassy GeO2 recrystallized in the X-ray beam preventing any further analysis. To circumvent the recrystallization of glassy GeO2 at high pressures, we propose to study it at low T conditions (<200 K) and multi-mbar pressures. The new data will not only provide information on the high P low T phase diagram of glassy GeO2 but will also give deep insights in the evolution of polyamorphic transitions at multi Mbar pressure.