The phase transition sequence in betaine calcium chloride dihydrate by adiabatic calorimetry

Abstract

Abstract The specific heat of (C3)3NCH2COO.CaCl2.2H2O (BCCD) has been measured by adiabatic calorimetry from 20 K to 330 K. This experimental study refers to the rich variety of phase transitions showed by this crystal and has permitted a precise characterization of its calorimetric response. Most of the previously reported phase transitions show a clear specific heat anomaly. In some cases, however, these measurements do not permit one to confirm the occurrence of phase transitions when they are related to very small jumps of the modulation wave vector. The results presented in this work confirm a noticeable relationship between the wave-vector behaviour and the associated phase transition entropy. In fact, this correlation has permitted an unambiguous identification of some of the crystal stable phases.