Fan, Chunmei; Liu, Shan; Liu, Jingyi; Wu, Binbin; Tang, Qiqi; Tao, Yu; Pu, Meifang; Zhang, Feng; Li, Jianfu; Wang, Xiaoli; He, Duanwei; Zhou, Chunyin; Lei, Li

CHINESE PHYSICS LETTERS

2022, 39, 0256-307X

Fan, Chunmei; Liu, Shan; Liu, Jingyi; Wu, Binbin; Tang, Qiqi; Tao, Yu; Pu, Meifang; Zhang, Feng; Li, Jianfu; Wang, Xiaoli; He, Duanwei; Zhou, Chunyin; Lei, Li

We observed an isostructural phase transition in the solid nitrogen lambda-N-2 at approximately 50 GPa accompanied by anomalies in lattice parameters, atomic volume and Raman vibron modes. The anomalies are ascribed to a slight reorientation of the nitrogen molecules, which does not seem to affect the monoclinic symmetry (space group P2(1)/c). Our ab initio calculations further confirm the phenomena, and suggest an optimized structure for the lambda-N-2 phase. In addition, a new high-pressure amorphous phase of eta '-N-2 was also discovered by a detailed investigation of the pressure-temperature phase diagram of nitrogen with the aim of probing the phase stability of lambda-N-2. Our result may provide helpful information about the crystallographic nature of dissociation transitions in diatomic molecular crystals (H-2, O-2, N-2, etc).