Direct and indirect studies of the electrocaloric effect in single crystalline ferrielectric (NH4)(2)SO4

Bondarev, V. S.; Mikhaleva, E. A.; Gorev, M. V.; Flerov, I. N./ Journal Of Alloys And Compounds/

The influence of an electric field on the phase transition parameters and the electrocaloric response in ferrielectric (NH4)2SO4 was studied using a universal multifunctional adiabatic calorimeter. The very low sensitivity of the phase transition temperature to the electric field, dT0/dE ≈ 5·10-3 K/(kV/cm), was shown to be the reason for the low maximum value of the intensive electrocaloric effect, ΔTAD, at E = 11 kV/cm: direct and indirect measurements gave the values of 0.01 K and 0.05 K, respectively. However, the extensive electrocaloric response revealed by an analysis of the entropy–temperature–electric field phase diagram was relatively large, with a value of ΔSECE ≈ − 19 J/kg K, due to the significant contribution of a jump in the excess entropy to the total value, δS0/ΔS0 ~ 0.37. An additional irreversible increase in temperature under the electric field was associated with the Joule effect and indicated a significant electrical conductivity of ammonium sulphate.