Indirect measurements of electrocaloric effect in ferroelectric thin films by positive-up-negative-down method

摘要

Positive-up-negative-down (PUND) polarization measurement was employed to indirectly estimate the electrocaloric (EC) effect in ferroelectric films. By subtracting the conductive component from the observed charge profile, the polarization values at various electric fields and temperatures were precisely determined. The estimated EC effect for an epitaxial Ba_0.3Sr_0.7O₃ thin film fabricated on SrRuO₃/SrTiO₃ (001) substrate showed the largest temperature change at around the ferroelectric-paraelectric phase transition temperature, which agrees with the theoretical prediction. On the other hand, the EC effect estimated by the conventional hysteresis loop measurement showed different peaking temperature from the theoretical prediction. The deviation became larger with lowering the measurement frequency. The observed results indicate the importance of precise evaluation of polarization for the examined temperature-electric field space.