Pressure-Induced Phase Transitions in LiNH2

Autor:	Stephen A. Gramsch, Russell J. Hemley, Dhanesh Chandra, Maddury Somayazulu, Raja Chellappa
Rok vydání:	2007
Předmět:	Phase transition Lithium amide Chemistry Pressure dependence Molecular physics Surfaces Coatings and Films Ion symbols.namesake Tetragonal crystal system chemistry.chemical_compound Lattice (order) Materials Chemistry symbols Organic chemistry Physical and Theoretical Chemistry Raman spectroscopy
Zdroj:	The Journal of Physical Chemistry B. 111:10785-10789
ISSN:	1520-5207 1520-6106
DOI:	10.1021/jp073206w
Popis:	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.
Databáze:	OpenAIRE
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