NONFERROELECTRIC PHASE-TRANSITIONS IN POTASSIUM HYDROGEN SULFATE {[}MERCALLITE, KHSO4]

Accurate measurements of some electrical properties combined with the differential thermal analysis (DTA) were made from room temperature up to 200-degrees-C for single crystals of KHSO4 (KHS). The data reveal the existence of two (non-ferroelectric) phase transitions around 100-degrees-C and 175-degrees-C. The first structural phase transition may involve only minor change in atomic positions and therefore it is not easy to detect. The existence of this phase is confirmed by the X-ray diffraction pattern. The data are correlated with the arrangement of the molecules in the unit cell including the hydrogen bonding system due to the two distinct HSO4 ions as well as the onset of the reorientational motion of the sulphate group.