Thickness-Dependent Electrocaloric Effect in Pb_0.9La_0.1Zr_0.65Ti_0.35O₃ Films Grown by Sol–Gel Process

Unlike bulk materials, many physical properties of thin-film materials depend on film thickness due to extrinsic effects such as residual stress and the dead layer. In this work, the effect of thickness on the electrocaloric properties of Pb_0.9La_0.1(Zr_0.65Ti_0.35)O₃(10/65/35) (PLZT) films grown by the sol–gel method was studied experimentally. In the sol–gel synthesis, the annealing process results in residual stress and the metal–dielectric contact generates a dead layer. These extrinsic effects influence the dielectric and ferroelectric properties of the thin films, and their roles are film thickness dependent. For PLZT of nanometer thickness (from 420 nm to 1080 nm), the permittivity and polarization, and their temperature dependences, showed strong dependence on film thickness. In particular, in the temperature range from 70°C to 350°C, the electrocaloric temperature change showed threefold improvement (from 0.2°C to 0.6°C) as the thickness was increased from 420 nm to 840 nm. This work will aid development of polycrystalline thin films including PLZT for electrocaloric applications.