Ammonium perchlorate NH₄ClO₄ (AP) was studied using synchrotron angle-dispersive X-ray powder diffraction (XRPD) and Raman spectroscopy. A diamond-anvil cell was used to compress AP up to 50 GPa at room temperature (RT). Density functional theory (DFT) calculations were performed to provide further insight and comparison to the experimental data. A high-pressure barite-type structure (Phase II) forms at ≈4 GPa and appears stable up to 40 GPa. Refined atomic coordinates for Phase II are provided, and details for the Phase I → II transition mechanics are outlined. Pressure-dependent enthalpies computed for DFT-optimized crystal structures confirm the Phase I → II transition sequence, and the interpolated transition pressure is in excellent agreement with the experiment. Evidence for additional (underlying) structural modifications include a marked decrease in the Phase II b′-axis compressibility starting at 15 GPa and an unambiguous stress relaxation in the normalized stress-strain response at 36 GPa. Above 47 GPa, XRD Bragg peaks begin to decrease in amplitude and broaden. The apparent loss of crystalline long-range order likely signals the onset of amorphization. Three isostructural modifications were discovered within Phase II via Raman spectroscopy. A revised RT isothermal phase diagram is discussed based on the findings of this study.

中文翻译：

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压力对高氯酸铵结构和晶格动力学的影响：结合实验和理论研究

高氯酸铵NH ₄ ClO ₄（AP）使用同步加速器角度色散X射线粉末衍射（XRPD）和拉曼光谱仪进行了研究。在室温（RT）下，使用金刚石砧盒将AP压缩至50 GPa。进行密度泛函理论（DFT）计算以提供进一步的见解和与实验数据的比较。高压重晶石型结构（第二阶段）形成于≈4GPa，并在高达40 GPa的情况下保持稳定。提供了阶段II的精确原子坐标，并概述了阶段I→II过渡机制的详细信息。为DFT优化的晶体结构计算的依赖于压力的焓确定了I→II相转变顺序，并且内插的转变压力与实验非常吻合。其他（基础）结构修改的证据包括第二阶段的显着减少b '轴可压缩性始于15 GPa，并且在36 GPa时归一化应力应变响应中的应力松弛明确。高于47 GPa，XRD布拉格峰的振幅开始减小并变宽。晶体远距离有序的明显损失可能预示着非晶化的开始。通过拉曼光谱法在II期发现了三个同构修饰。根据这项研究的结果，讨论了修订的RT等温相图。