Structural transitions in NaNH₂ via recrystallization under high pressure

Multiple phase transitions are detected in sodium amide (NaNH₂), an important hydrogen storage material, upon compression in diamond anvil cells (DAC) by using Raman spectroscopy and x-ray diffraction (XRD) measurements. Additional Bragg reflections appear on lower and higher angle sides of the original ones at~1.07 GPa and 1.84 GPa, accompanied by obvious changes in Raman spectroscopy, respectively. It reveals that NaNH₂ undergoes the high-pressure phase sequence (α-β-γ) up to 20 GPa at room temperature. Spectral analysis indicates an orthorhombic structure with PBAN space group for the γ phase. We also experimentally observe high pressure induced recrystallization in alkaline amide compounds for the first time.