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Updated: Jun 13, 2025

Synthesis and Microdiffraction at Extreme Pressures and Temperatures
Published on: October 7, 2013
Phase Transitions of NH4Cl under Low Temperature or High Pressure Observed by Sequential Powder X-ray Diffraction
Kazuki Komatsu1, Takanori Murakami1, Satoshi Nakano2
1Geochemical Research Center, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Abstract:
The compression behavior and phase transitions of NH4Cl were investigated by using X-ray diffraction. A clear volume anomaly at 0.7-1.0 GPa confirmed the first-order nature of the phase II-IV transition at 298 K. Low-temperature X-ray diffraction measurements at ambient pressure revealed a slight hysteresis in this transition, suggesting differences in the degree of order of the orientation of the NH4+ ion in the cooling and heating processes. We first clarified that the crystal structure of phase V has antiferro-ordered orientation with a tetragonal system, and the structural analysis of phase V indicated that hydrogen bonding plays a key role in the alternately varied N-Cl distances.
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