Pressure-induced phase transitions in LiNH2 |
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Authors: | Chellappa Raja S Chandra Dhanesh Somayazulu Maddury Gramsch Stephen A Hemley Russell J |
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Institution: | Materials Science & Engineering Division, Department of Chemical & Metallurgical Engineering (MS 388), University of Nevada, Reno, Nevada 89557, USA. rchellappa@ciw.edu |
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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. |
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