1. Thermodynamics

1.1 Writing the two coupled equations

To define the electrocaloric effect, we need to recall a few elements of classical thermodynamics. The electrocaloric effect cannot be dissociated from the pyroelectric effect, of which it is the symmetrical (in the sense of electrical/thermal energy conversion).

The fundamental quantities of pyroelectricity are, for the electrical part, the field E _k and the electrical displacement D _k ("k" index from 1 to 3 translating the three possible directions for the electrical quantities), and, for the thermal part, the temperature T and the entropy S. Assuming that these four quantities are state functions, it is possible to formalize the...