An inverse ferroelastic type phase transition and electric properties in bis(ethylenediammonium)tetrachlorozincate chloride crystal

Abstract

Here we present TGA, DSC, dielectric studies and polarized microscopy observations of bis-ethylenediammonium tetrachlorozinc dichloride. In our studies, we found a high-temperature first-order phase transition at about 478/470 K for the heating/cooling cycle, respectively. The reversibility of the phase transition was detected by DSC and dielectric measurements and also by polarized microscopy observations. The appearance of a ferroelastic-type domain structure phase above the phase transition temperature indicates a reduction in symmetry during the heating cycle. The domain walls observed in the (100) plane are characteristic of a ferroelastic-type phase transition and can be classified as mmmF2/m Aizu species. The reduction in symmetry above the phase transition temperature allows us to classify the phase transition at 476 K as a "reverse" type. Dielectric studies in the frequency range of 40 Hz - 8 MHz allowed to estimate the activation energy for conduction and relaxation processes both with increasing and decreasing temperature. Activation energies obtained both from conductivity (σdc) measured in the temperature range from 445 to 485 K and relaxation process are practically the same both for low- and high-temperature phases as well. Taking into account the results for all directions (a, b, c) and all temperatures, conductivity is 10−7 – 10−4 S/m and is within the range characteristic for semiconductors (10−8 – 106) S/m. The conductivity and relaxation activation energies determined for the directions (a, b, c) have values in the range from 0.58 to 3.7 eV, which are also within the range characteristic for semiconductors. Electrical properties show clearly anisotropic character of the studied material.