THE PHASE-TRANSITION SEQUENCE IN TETRAMETHYLAMMONIUM CADMIUM CHLORIDE(TMCC) - [N(CH3)(4)]CDCL3

The structural phase transitions in [N(CH3)(4)]CdCl3 were investigated by means of adiabatic calorimetry and thermal expansion measurements. Two phase transitions have been studied on cooling and on heating at about 104 K and 118 K. The shapes of the observed specific heat anomal ies, as well as the existence of thermal hysteresis, confirm the first -order character previously assigned to these phase transitions. From the experimental data and the harmonic specific heat obtained from the known frequencies of the vibrational modes, a calculation of the Grun eisen parameter as a function of the temperature is also given. Finall y, the suitability of different Landau potentials for the two phase tr ansitions is briefly discussed.