Tailoring high-field energy storage and dual-mode electrocaloric response in relaxor ferroelectric thin film

Abstract

Ferroelectric and antiferroelectric thin and thick films with strong electrocaloric (EC) responses are attractive for solid-state cooling. In this study, 0.75PbMg_1/3Nb_2/3O₃–0.25PbTiO₃ (PMN-25PT) relaxor ferroelectric thin films deposited on LSAT substrates by pulsed laser deposition exhibit a giant negative EC effect near 150 °C, with a maximum temperature change of −38.3 K and an entropy change of −29.4 J kg⁻¹ K⁻¹. A large positive EC effect is also observed near 120 °C, yielding ΔT = 33.4 K and ΔS = 27.5 J kg⁻¹ K⁻¹, comparable to the best reported values. The films show nanoscale columnar grains that promote polar nanoregions, leading to high polarization, large dielectric breakdown strength, and a diffuse, frequency-dependent dielectric response. Polarization–electric field loops measured from 30 °C to 190 °C reveal the excellent thermal stability of energy storage, which remains robust after 10⁸ charge–discharge cycles. Moreover, the films demonstrate efficient harvesting of low-grade waste heat, achieving an energy conversion density of ∼18.7 J cm⁻³ per cycle over 0–2.5 MV cm⁻¹ and a wide temperature range of 30–140 °C, as evaluated using pyroelectric Olsen cycles. These results highlight PMN-25PT thin films as promising candidates for advanced energy storage and electrocaloric cooling applications.