Exploration of the Energetic Material Ammonium Perchlorate at High Pressures: Combined Raman Spectroscopy and X-ray Diffraction Study

High-pressure behaviors of ammonium perchlorate (NH4ClO4), a widely used energetic oxidizer, have been investigated using in situ angle-dispersive X-ray diffraction (XRD) and Raman spectroscopy experiments up to 22.0 and 20.4 GPa, respectively. A sluggish structural transformation is identified, which started at ∼2.4 GPa and completed at ∼10.6 GPa. The crystal structure of high pressure (phase II) is refined to possess a symmetry of P2. The structural transformation is indicated by the obvious changes in XRD patterns, Raman spectra, and discontinuities of peak positions. Variations in lattice constants and volume of unit cell of the ambient structure (phase I) up to ∼10.0 GPa are also presented. The compressibility of phase I is anisotropic. The compression ratio of baxis is larger than that of aand caxes. The bulk modulus of phase I is B0= 24.5(4) GPa, and its first pressure derivative is B0′ = 4.5(2). The phase transition is reversible, as the XRD pattern transformed to the initial profile upon release of pressure. On the basis of the Raman and XRD analysis, the high-pressure-induced phase transition of ammonium perchlorate is proposed to be associated with rearrangement of hydrogen-bonded networks.