Multifunctional flexible ferroelectric thick-film structures with energy storage, piezoelectric and electrocaloric performance

Abstract

As a major challenge, sustainable energy management and energy self-sufficiency require microsystems that manage multiple energy operations in a single device. In this work, flexible thick-film structures with promising energy storage and electrocaloric cooling capabilities as well as piezoelectric properties are developed. The functional thick-film layer is based on relaxor-ferroelectric 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–35PT) directly deposited on a flexible polyimide substrate by an aerosol deposition method. The thick-film structures exhibit a promising recoverable energy-storage density of 10.3 J cm⁻³. After extensive bending tests, the structures showed no signs of degradation. The high bendability and durability are confirmed by stable energy storage properties after bending up to a radius of 1.5 mm (2.4% bending strain) and 10⁵ repeated bending cycles. The developed thick-film structures also exhibit a piezoelectric coefficient d₃₃ of ∼80 pm V⁻¹. Using two direct electrocaloric measurement methods, we demonstrated that the electrocaloric temperature change in the prepared PMN–35PT thick-film structures reaches a maximum of 0.87 K at 63.5 °C and 300 kV cm⁻¹, which exceeds the value of 0.72 K at ∼65 °C and 60 kV cm⁻¹ reported for bulk ceramics of the same composition. The PMN–35PT thick films prepared here are thick-film structures with excellent flexibility, promising for future multifunctional microsystems that manage multiple energy operations, enabling comprehensive energy harvesting, storage and conversion to thermal energy.