In situ observation of a first-order liquid–liquid transition in phosphorus

Abstract Recently, we have found an abrupt, pressure-induced structural change between two distinct forms of liquid phosphorus at about 1 GPa by an in situ X-ray diffraction method. X-ray diffraction of liquid phosphorus was measured up to 4.6 GPa and that of red amorphous phosphorus was measured at atmospheric pressure and 3.0 GPa. A model liquid of uncorrelated P4 molecules roughly reproduces the structure factor of the low-pressure form. On the other hand, there are similarities in the structure factors of the high-pressure form, red phosphorus and liquid arsenic, indicating that the high-pressure form has a polymeric nature.