Electro-thermal actuation in percolative ferroelectric polymer nanocomposites

Piezoelectric actuators play a critical role in precision positioning devices; however, materials with high actuation strain and mechanical energy density are rare. Here a composite of poly(vinylidene fluoride) and TiO2 demonstrates superior performance in these metrics, with the ferroelectric transition driven by Joule heating. The interconversion between electrical and mechanical energies is pivotal to ferroelectrics to enable their applications in transducers, actuators and sensors. Ferroelectric polymers exhibit a giant electric-field-induced strain (>4.0%), markedly exceeding the actuation strain (<= 1.7%) of piezoelectric ceramics and crystals. However, their normalized elastic energy densities remain orders of magnitude smaller than those of piezoelectric ceramics and crystals, severely limiting their practical applications in soft actuators. Here we report the use of electro-thermally induced ferroelectric phase transition in percolative ferroelectric polymer nanocomposites to achieve high strain performance in electric-field-driven actuation materials. We demonstrate a strain of over 8% and an output mechanical energy density of 11.3 J cm(-3) at an electric field of 40 MV m(-1) in the composite, outperforming the benchmark relaxor single-crystal ferroelectrics. This approach overcomes the trade-off between mechanical modulus and electro-strains in conventional piezoelectric polymer composites and opens up an avenue for high-performance ferroelectric actuators.