High-pressure amorphous nitrogen

Abstract

The phase diagram and stability limits of diatomic solid nitrogen have been explored in a wide pressure-temperature range by several optical spectroscopic techniques. A narrow-gap semiconducting phase $\ensuremath{\eta}$ has been found to exist in a range of 80--270 GPa and 10--510 K. The vibrational and optical properties of the $\ensuremath{\eta}$ phase produced under these conditions indicate that it is largely amorphous and back transforms to a new molecular phase. The band gap of the $\ensuremath{\eta}$ phase is found to decrease with pressure indicating possible metallization by band overlap above 280 GPa.