Structure of Intermediate Phase II of LiNH2 under High Pressure

A new intermediate phase (phase II) was found between phases I and III in LiNH2 in the pressure range of 10 to 13 GPa through the analysis of infrared and powder X-ray diffraction measurements to 25 GPa at room temperature. This result agreed with the prediction of a stable phase between phases I and III through theoretical calculations. Powder X-ray diffraction measurement and DFT calculation showed that this phase has a monoclinic structure with space group C2/c (Z = 8), which is the same structure as that of a slightly tilted crystal lattice of the Fddd structural model. The enthalpy of the C2/c structure was also found to be almost the same as that of the Fddd structure.