title: Melting and phase transitions of nitrogen under high pressures and temperatures.
abstract: Dense nitrogen exhibits fascinating molecular and extended polymorphs as well as an anomalous melt maximum at high temperatures. However, the exact solid-liquid phase boundary is still the subject of debate, as both creating and probing hot dense nitrogen, solid and fluid alike, poses unique experimental challenges. Raman studies of nitrogen were performed to investigate the melting curve and solid-solid phase transitions in the pressure-temperature range of 25 to 103 GPa and 300 to 2000 K. The solid-liquid phase boundary has been probed with time-resolved Raman spectroscopy on ramp heated nitrogen in diamond anvil cell (DAC), showing a melting maximum at 73 GPa and 1690 K. The solid-solid phase boundaries have been measured with spatially resolved micro-confocal Raman spectroscopy on resistively heated DAC, probing the δ-ɛ phase line to 47 GPa and 914 K. At higher pressures the θ-phase was produced upon a repeated thermal heating of the ζ-phase, yet no evidence was found for the ι-phase. Hence, the present results signify the path dependence of dense nitrogen phases and provide new constraints for the phase diagram.
authors.affiliation: Department of Chemistry and Institute for Shock Physics, Washington State University, Pullman, Washington 99164, USA.
authors.forename: Dane
authors.initials: D
authors.lastname: Tomasino
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Jenei
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: William
authors.initials: W
authors.lastname: Evans
authors.affiliation: Department of Chemistry and Institute for Shock Physics, Washington State University, Pullman, Washington 99164, USA.
authors.forename: Choong-Shik
authors.initials: CS
authors.lastname: Yoo