Influence of thermal conditions on the electrocaloric effect in a multilayer capacitor based on doped BaTiO3

We present the results of studies of thermal expansion, heat capacity, permittivity, polarization and the influence of different thermal conditions on the intensive electrocaloric effect (ECE), Delta T-AD, in a commercial multilayer capacitor based on doped BaTiO3. Investigations in a wide temperature range revealed one anomaly in the behavior of the physical properties at about 290K characteristic for the relaxors. Direct measurements showed a high reversibility of ECE under equilibrium thermal conditions. Good agreement was found between the values of Delta T-AD determined by direct and indirect measurements at the electric field up to 15.4 kV/cm. Quasi-isothermal conditions lead, firstly, to decrease of large Delta T-AD approximate to 0.94K obtained in adiabatic conditions under E = 308 kV/cm to 0.87 K, and, secondly, the appearance of a difference between the values of Delta T-ON and Delta T-OFF determined when the electric field is applied and removed. Using this phenomenon and changing the frequency of the periodic electric field, E = 15: 4 kV/cm, the effect of cooling was obtained equal to (Delta T-ON + Delta T-OFF)/2](max) = -0.032 K. The results obtained are useful for further development of the electrocaloric refrigeration technique without thermal switches.