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 newly characterized narrow-gap semiconducting phase η has been found to exist in a range of 80--270 GPa and 10--510 K. The vibrational and optical properties of the η phase produced under these conditions indicate that it is largely amorphous and back transforms to a new molecular phase. The band gap of the η phase is found to decrease with pressure indicating possible metallization by band overlap above 280 GPa.
@article{arxiv.cond-mat/0105101,
title = {High-Pressure Amorphous Nitrogen},
author = {Eugene Gregoryanz and Alexander F. Goncharov and Russell J. Hemley and Ho-kwang Mao},
journal= {arXiv preprint arXiv:cond-mat/0105101},
year = {2009}
}