Calorimetric study of the ferroelectric (N(CH3)4)2ZnCl4: critical behaviour of the commensurate-incommensurate phase transition

Specific heat measurements performed on the ferroelectric (N(CH 3 ) 4 ) 2 ZnCl 4 reveal that the phase transition occurring in this compound can be classified into two groups. The commensurate to incommensurate to ferroelectric to paraelectric sequence belongs to the first group, whereas in the second group, for which a new anomaly was detected, the authors have three phase transitions associated with the organic group movements. The critical behaviour for the commensurate-incommensurate phase transition is discussed.