Electrical, thermal and calorimetric evidence for a new high temperature phase transition in potassium perchlorate

The electrical resistivity (rho), the relative permittivity (epsilon) in addition to the thermal conductivity (lambda) and the thermal heat capacity (C-p) were accurately measured in the temperature range 40-320 degrees C for polycrystalline samples of potassium perchlorate (KClO4). The data suggest that the compound undergoes two structural phase transitions at 147 degrees C and 308 degrees C. It seems likely that the first structural phase transition may involve only minor change in atomic positions, like the phase transition in potassium chlorate (KClO3). Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were also performed. The DTA results strongly confirmed the existence of the two structural phase transitions at the above mentioned temperatures. The TGA plot showed the absence of any actual loss in weight at the transition temperature regions. The data are correlated with the crystal structure including ClO4 ions and the other perchlorate compounds.