PHASE-TRANSITIONS IN CAHPO4 AND BAHPO4 ABOVE ROOM-TEMPERATURE

Phase stability of MHPO4 (M = Ca, Ba) in the solid state was studied b y means of differential scanning calorimetry, high-resolution ac-calor imetry and ion-mobility analysis above room temperature. Both salts sh owed a sequence of phase transitions that were very dependent on mecha nical and thermal treatments of the samples. Since similar observation s have been previously reported for many alkali-metal hydrogen double salts, it seems then plausible the involment of hydrogen bonds in the structural disorder that marks the onset of the fast-ion state in all these salts at higher temperatures.