SPECIFIC-HEAT OF BETAINE CALCIUM-CHLORIDE DIHYDRATE

The molar heat capacity of the ferroelectric betaine calcium chloride dihydrate (BCCD). (CH3)3NCH2CO0.CaCl2.2H2O, was measured between 2 K and 300 K and the different phase transitions are investigated. The transition from normal to incommensurate phase shows a typical secondorder anomaly at Ti = 164 K. At the incommensurate-commensurate transition (lock-in transition) at 116 K a sharp anomaly in the heat capacity was observed indicating a first order transition. The sequence of the phase transitions is characterized by their entropies and enthalpies of transition. A possible relation between the modulation vector Δq* and the entropy change ΔS is discussed. © 1990, Taylor & Francis Group, LLC. All rights reserved.