X-RAY STUDY ON THE PHASE-TRANSITIONS IN TRIAMMONIUM HYDROGEN DISULFATE CRYSTALS AND DEUTERATED CRYSTALS

The structural phase transitions in triammonium hydrogen disulfate crystals and deuterated crystals below room temperature have been studied by X-ray diffraction. Three phases are observed in the temperature range from 25°C down to — 160°C. The space groups in three different phases are identified as C2/c, P2/n (or Pn), and C2 for (NH4)3H(SO4)2and (ND4)3D(SO4)2crystals. No isotope effect on the structural phase transitions in these crystals could be detected by these studies. The occurrence of structural phase transitions caused by the reorientation of SO4groups and/or the shift of oxygen atoms from the sulfate atom in the SO4group are suggested from the diffraction photographs. © 1992, Taylor & Francis Group, LLC. All rights reserved.