Phase Transitions in Crystalline Divalent Metal Dicalcium Propionates. I. Calorimetric and Dielectric Investigations of Strontium- and Lead Dicalcium Propionates

Abstract

Heat capacities have been measured for strontium and lead dicalcium propionates from 15 to 300°K with an adiabatic-type calorimeter in connection with the ferroelectric phase transition of strontium salt. The heat capacities, enthalpies, entropies and Gibbs energy functions in the standard state have been determined. For the strontium salt, the transition temperature, the heat of transition, and the entropy of transition for the ferroelectric phase transition are 282.6°K, 159.6 cal.mol−1, and 0.6 e.u. respectively. Another phase transition was discovered at 104°K; the heat and entropy of this transition amount to 255 cal.mol−1 and 3.2e.u. respectively.For the lead salt, a phase transition was found at 191.5°K, and the heat and the entropy of the transition are 1160.0 cal. mol−1 and 5.8 e.u. respectively. Low frequency dielectric constants have been measured for the lead salt from the liquid nitrogen temperature to 90°C. A discontinuous change in the dielectric constants at 183°K and another dielectric anomaly at 60°C have been observed. The absence of evidence of ferroelectricity above room temperature has also been confirmed.The ferroelectric phase transition of the strontium salt has been treated by the Bragg-Williams theory. The temperature dependence of the spontaneous polarization has tentatively been interpreted with torsional oscillations of the methyl groups of the propionate anions.