Mott-Anderson transition, where a disordered system undergoes insulator – metal transition (IMT), is a very rare event. Some years ago we have shown that SiO turns metallic under 12 GPa, while its X-ray absorption data shows a typical hump of an amorphous material up to 30 GPa. This turned SiO to be a good candidate to demonstrate a Mott-Anderson transition.

In order to rule out the possibility of SiO disproportionation to SiO2 and Si which might be the cause of metallization it would be beneficial to measure EXAFS and Xanes on SiO in-situ. However, such an experiment is not feasible due to the high absorption of the diamond anvils at the wavelength that corresponds to the K-edge of Si. Thus we have recently studied the analogue material germanium monoxide under high pressure using room temperature XRD and cryogenic resistance measurements, and found that it is amorphous up to at least 23 GPa, and that around 12 GPa it seems to undergo an IMT.

Following this result we performed EXAFS and XANES on the GeO K-edge, at the energy dispersive branch of the beamline (I20-EDE) at DIAMOND UK, to check the possibility of disproportionation of GeO and to gain valuable information on the possible change in band structure that relates to the IMT, which might help assert if it is the lone-pair of the Ge atom that delocalizes.

We have found full reversibility upon downstroke, and thus ruled out the possibility of GeO disproportionation, confirming that GeO indeed undergoes the rare event of Mott-Anderson metallization. Detailed analysis of changes in GeO band structure and efforts to point out the electronic states that undergo delocalization are underway.