Chellappa Raja S, Chandra Dhanesh, Somayazulu Maddury, Gramsch Stephen A, Hemley Russell J
Materials Science & Engineering Division, Department of Chemical & Metallurgical Engineering (MS 388), University of Nevada, Reno, Nevada 89557, USA.
J Phys Chem B. 2007 Sep 13;111(36):10785-9. doi: 10.1021/jp073206w. Epub 2007 Aug 21.
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.
已在高达25吉帕的压力下对氨基锂（LiNH₂）进行了原位高压拉曼光谱研究。LiNH₂拉曼光谱中压力诱导的变化表明，从环境压力下的α-LiNH₂（四方晶系，I）到这里表示为β-LiNH₂的高压相的相变在约12吉帕开始，并在约14吉帕完成。减压时，该相变是可逆的，在约8吉帕时α-LiNH₂相恢复。N-H内部伸缩振动模式（ν([NH₂]⁻)）的频率随压力增加，并且在约12.5吉帕出现对应于高压β-LiNH₂相的新伸缩振动模式。超过约14吉帕后，N-H伸缩振动模式在较低频率处形成两个肩峰。晶格模式显示出丰富的压力依赖性，表现出多重分裂，并且在高于约14吉帕的压力下变得清晰可辨。这表明在高压β-LiNH₂相的晶格中[NH₂]⁻离子存在取向有序化。
