title: Pressure-induced phase transitions in LiNH2.
abstract: In situ high-pressure Raman spectroscopy studies on LiNH2 (lithium amide) have been performed at pressures up to 25 GPa. The pressure-induced changes in the Raman spectra of LiNH2 indicates a phase transition that begins at approximately 12 GPa is complete at approximately 14 GPa from ambient-pressure alpha-LiNH2 (tetragonal, I) to a high-pressure phase denoted here as beta-LiNH2. This phase transition is reversible upon decompression with the recovery of the alpha-LiNH2 phase at approximately 8 GPa. The N-H internal stretching modes (nu([NH2]-)) display an increase in frequency with pressure, and a new stretching mode corresponding to high-pressure beta-LiNH2 phase appears at approximately 12.5 GPa. Beyond approximately 14 GPa, the N-H stretching modes settle into two shouldered peaks at lower frequencies. The lattice modes show rich pressure dependence exhibiting multiple splitting and become well-resolved at pressures above approximately 14 GPa. This is indicative of orientational ordering [NH2]- ions in the lattice of the high-pressure beta-LiNH2 phase.
authors: Materials Science & Engineering Division, Department of Chemical & Metallurgical Engineering (MS 388), University of Nevada, Reno, Nevada 89557, USA. rchellappa@ciw.edu
authors: Raja S
authors: RS
authors: Chellappa
authors: Dhanesh
authors: D
authors: Chandra
authors: Maddury
authors: M
authors: Somayazulu
authors: Stephen A
authors: SA
authors: Gramsch
authors: Russell J
authors: RJ
authors: Hemley