We report angle dispersive X-ray diffraction (XRD) measurements and Raman spectroscopy on NH₄Br up to 70.0 GPa at room temperature. Three thermodynamically stable phases (phases II, IV, and V) are confirmed and a new possible phase (phase VI) of P2₁/m symmetry is proposed whose structure was established from Rietveld refinement of synchrotron XRD data for the first time. The phase sequence observed in NH₄Br is in accordance with phase II → IV → V → VI. Phase V transforms into phase VI at about 57.8 GPa with a huge volume reduction of 30%. Still, the intramolecular distances are analyzed to better understand the nature of structures. The H–H interactions become markedly more important as the N–Br distances are compacted, which is probably the reason of the kink of symmetric stretching band (ν ₁) at the transition pressure.

中文翻译：

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压力引起的NH4Br结构变化

我们报告了室温下高达70.0 GPa的NH ₄ Br的角度色散X射线衍射（XRD）测量和拉曼光谱。确定了三个热力学稳定的相（相II，IV和V），并提出了新的可能的P 2 ₁ / m对称相（相VI），其结构是通过同步加速器XRD数据的Rietveld精炼首次建立的。在NH _4中观察到的相序Br符合II→IV→V→VI相。V相在约57.8 GPa时转变为VI相，体积减少了30％。尽管如此，分子内的距离进行了分析，以更好地了解结构的性质。的H-H的相互作用成为作为N-溴距离明显更重要被压实，这可能是对称伸缩带的扭结的原因（ν ₁在过渡压力）。