A paper led by Associate Professor Kazuki Komatsu and Takanori Murakami, a graduate of our laboratory, has been published in Inorganic Chemistry.
Ammonium chloride (NH4Cl) is a representative material that undergoes order-disorder phase transitions through the orientational ordering of ammonium ions. In this study, sequential powder x-ray diffraction measurements were conducted at low temperatures and high pressures to examine structural changes with temperature and pressure in detail. Our XRD data confirm that the transition at room temperature and 0.7–1.0 GPa is first-order accompanied by a volume change. We also revealed differences in the degree of ammonium-ion ordering between cooling and heating at low temperatures. Furthermore, the high-pressure phase V was shown for the first time to have a tetragonal structure with alternating ammonium-ion orientations. We showed thathydrogen bonding plays an important role in the formation of phase V.
Komatsu K., Murakami T., Nakano S., and Kagi H. (2025) Phase transitions of NH4Cl under low temperature or high pressure observed by sequential powder X-ray diffraction. Inorganic Chemistry, 64, 13079-12085.