Increased saturation field as the origin of the giant electrocaloric effect in Ba_0.8Sr_0.2TiO₃ thin films

We investigated the electrocaloric (EC) effects in epitaxial Ba_0.8Sr_0.2TiO₃ (BSTO) thin films grown on LaAlO₃ and MgO substrates and in BSTO sol-gel thin films grown on Si substrates. We compared the EC effects in two forms of BSTO to confirm whether the giant EC effect recently observed in the polycrystalline thin film is an intrinsic effect or an extrinsic effect exclusively occurring in polycrystalline thin films with nano-sized grains. The EC effect in our BSTO single crystals exhibited a moderate EC temperature change over a broad temperature range. On the other hand, the EC effect in the BSTO sol-gel film was observed over a narrow temperature range with a giant ΔT of about 14 °C. We claim that this giant EC effect is due to the increased saturation field related to the small grain size in the sol-gel thin film.