Heat capacity measurements and phase transition of crystalline 4,4″-difluoro-p-terphenyl

The heat capacity of 4,4″-difluoro- p -terphenyl was measured between 8 and 303 K by adiabatic calorimetry. A phase transition associated with molecular twisting was observed as a sharp peak at (127.05 ± 0.05) K. The enthalpy and the entropy of transition were determined as (180 ± 20) J mol −1 and (1.41 ± 0.15) J K −1 mol −1 , respectively. It is pointed out that this phase transition lies in the border region between an order-disorder and displacive-type transition under normal pressure. The apparatus used for calorimetry is described.