The coexistence of different superperiods in the vicinity of phase transitions in(NH4)2ZnCl4

Abstract

Abstract More detailed X-ray diffraction studies of the phase transitions observed earlier by the authors have made it possible to find for (NH4)2ZnCl4 with decreasing temperature the following sequence of phases (represented by the cell parameter c of the pseudohexagonal axis): I: c o, II: 4c o, III: (3.5c o, 4c o), IV: (3c o, 3.5c o, 4c o), V: (3c o, 4c o), VI: 3c o, c o being the fundamental period of the structure and the coexisting superperiods (in parentheses). A coexistence of two or more superperiods can be described as one---correspondingly longer---superperiod. The modulation parameter, the intensities of selected normal and satellite reflections as well as their peak halfwidths were studied as functions of temperature in the vicinity of the phase transitions.