Single crystal XRD investigation of a critical point terminated phase boundary in solid oxygen

Our research proposal is to study the region of the phase diagram of oxygen extending between 8 and 50 GPa at room and low temperatures using the diamond anvil cell coupled to flux cryostats in order to clarify the open issues present in literature and to confirm and extend to low temperatures the results of our recent diffraction experiment at room temperature (Petra, I-20200536 EC). In particular we plan to investigate and verify the existence of a phase boundary within the region of the epsilon phase at low temperatures, separating the epsilon1 (made of O8 molecules=4XO2 molecules having spin 1) from the epsilon0 (made of O8 molecules=4XO2 molecules having spin 0) as it has been recently proposed by simulations. We have recently obtained in Petra the evidence of important structural changes in the epsilon phase at room temperature which might be the epsilon1 to epsilon0 transition and which needs to be confirmed and studied also at low temperatures.