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 d ue to the two distinct HSO4 ions as well as the onset of the reorienta tional motion of the sulphate group.