EVIDENCE OF 2 COMPETITIVE PHENOMENA INVOLVED IN THE PHASE-TRANSITION PROCESS AT 144 K IN K2ZNCL4 FROM X-RAY-DIFFRACTION AND DSC EXPERIMENTS

Differential scanning calorimetry and x-ray diffraction experiments pe rformed in K2ZnCl4 have clearly revealed that two phenomena are involv ed in the phase transition process at 148 K. The first one corresponds to a slow reorganization of the tetrahedron configuration responsible for the development of a diffuse scattering localized on (a + b*)/2 points of the reciprocal space. The second phenomenon corresponds to t he growth of the (a + b*)/2 superstructure phase. A very new feature results from observation of a competitive character between these two phenomena. It is shown that the kinetic behaviour of the first phenome non and its possible correlation to the crystal growth defects are cer tainly involved in the phase transition process at 148 K.