DIELECTRIC, CALORIMETRIC, AND NEUTRON-DIFFRACTION STUDIES OF THE PHASE-TRANSITION IN K2ZNCL4 AT 145-K

The ferroelectric-to-ferroelectric phase transition of K2ZnCl4 at 144.5 K has been studied by dielectric, calorimetric, and neutron diffraction measurements. In addition to the first order transition at 144.5 K, there is a break on the dielectric constant along the a-direction at 148.0 K, where a slight anomaly in the specific heat is found by the a.c. calorimetry. Below 144.5 K superlattice reflections are found at (h + 0.5, k + 0.5, l). Weak satellite reflections are found between 145.5 K and 148.0 K at the incommensurate positions of (2.5 +/- delta, 1.5 +/- delta, 0). The misfit parameter delta is about 0.04 and it is almost temperature independent.