- phase diagram and structural transformations of molten PO under pressure

Brazhkin, V. V.*; Katayama, Yoshinori; Lyapin, A. G.*; Saito, Hiroyuki

The PO compound is an archetypical glass-forming oxide. We present the in situ X-ray diffraction study of the pressure-temperature phase diagram of PO and of the liquid PO structure under high pressure up to 10 GPa. We found that structural transformation in the liquid PO under pressure is unique and includes three stages: first, the disappearance of the intermediate range order of the melt together with a slow increase in the average first-coordination number (P-O and O-P neighbors) up to 4 GPa; second, the "normal" compression almost without structural modification at higher pressures up to 8-9 GPa; and, finally, the abrupt change of the short-range order structure of the liquid with the jumplike increase at 9-10 GPa.