Abstract:

Synchrotron radiation single crystal X-ray diffraction (XRD), Raman spectroscopy and infrared spectroscopy were used to analyze natural ammonium chloride (NH₄Cl) under high pressure. The results show that NH₄Cl transforms from phase IV (space group ) to phase V (space group P4/nmm) at 13.6 GPa. The parameters of the third-order Birch-Murnaghan equation of state are determined with K₀=24.9(1) GPa, V₀=56.4(1) ų, K₀′=5.5 for phase IV, and K₀=35(25) GPa, V₀=110(11) ų, K₀′=3.8(13) for phase V. The Raman spectrum of NH₄Cl shows new peaks and discontinuity at 13.7 GPa, and the Raman shift are linearly related to pressure. dν_i/dP and Grüneissen parameters for each vibration of phase IV and V are obtained. The infrared spectrum of N—H vibration split at 11.7–14.8 GPa. The transition pressures from phase IV to V of NH₄Cl, NH₄Br and NH₄I decrease in turn, which are inversely proportional to the anion radius. 

Key words: ammonium chloride, high pressure phase transition, X-ray diffraction, Raman spectroscopy, infrared spectroscopy 

摘要：

在高压环境下, 对天然卤砂(NH₄Cl)进行同步辐射单晶X射线衍射(XRD)、拉曼光谱和红外光谱分析。结果表明, NH₄Cl在13.6 GPa 发生相变, 从IV相(空间群为)变为V相(空间群为P4/nmm); IV相和V相NH₄Cl的三阶Birch-Murnaghan状态方程参数分别为 K₀=24.9(1) GPa, V₀=56.4(1) ų, K₀′=5.5以及K₀=35(25) GPa, V₀=110(11) ų, K₀′=3.8(13)。NH₄Cl的拉曼光谱在13.7 GPa出现新峰和不连续变化, 其拉曼位移与压强呈现线性关系, 据此获得IV相和V相NH₄Cl各拉曼振动的位移量随压强的变化, 并计算格林乃森参数。NH₄Cl的红外光谱在11.7~14.8 GPa出现N—H振动峰分裂。NH₄Cl, NH₄Br和NH₄I的IV-V相变压强依次降低, 表现出与阴离子半径成反比的规律。

关键词: 氯化铵, 高压结构相变, X射线衍射, 拉曼光谱, 红外光谱