CALORIMETRIC AND DIELECTRIC STUDIES OF PHASE TRANSITION IN TlNO2 CRYSTAL

The molar heat capacity of TlNO2 crystal has been measured between 14 and 355 K with an adiabatic calorimeter. A heat capacity anomaly due to a phase transition was found at (282.4±0.5) K. The enthalpy and entropy changes of the transition are 6400 Jmol−1 and 23.6 J K−1mol−1, respectively. The complex dielectric permittivity was measured in the frequency range between 200 Hz and 100 kHz. Dielectric dispersion and relaxation were found between 80 and 180 K. The activation enthalpy derived from the dielectric measurement is 19 kJ mol−1 and is possibly related to the reorientation of the NO2− ion.