One of the key problems in the existing lead-free piezoelectrics lies in how to further boost their dynamic piezoelectric responses, i.e., electrostrain and dynamic piezoelectric constants, in an effective and facile manner, making them comparable to those of widely used lead-based counterparts. In this work, a new strategy is developed to largely improve the dynamic piezoelectric properties of lead-free ferroelectrics using phase field simulations by combining the relaxor/ferroelectric crossover rendering potentially reversible electrostrain and the morphotropic phase boundary (MPB) providing easy paths of ferroelectric polarization rotations. Following the guidance of simulation results, Mn-doped (Bi 0.5 Na 0.5)TiO 3-BaTiO 3 lead-free piezoelectric ceramics with relaxor/MPB crossover are synthesized. A large reversible electrostrain (S max) of 0.55% with a promising piezoelectric constant d 33 * (S max /E max) of 917 pm V-1 at the designed relaxor/MPB crossover is obtained, outperforming almost all practical lead-free counterparts when taking both electrostrain and dynamic piezoelectric constants into consideration. The strategy of utilizing relaxor/MPB crossover provides a new route for enhancing the dynamic piezoelectric responses in lead-free ferroelectric perovskites.

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The flexoelectric effect, which manifests itself as a strain-gradient-induced electrical polarization, has triggered great interest due to its ubiquitous existence in crystalline materials without the limitation of lattice symmetry. Here, we propose a flexoelectric photodetector based on a thin-film heterostructure. This prototypical device is demonstrated by epitaxial LaFeO 3 thin films grown on LaAlO 3 substrates. A giant strain gradient of the order of 10 6 /m is achieved in LaFeO 3 thin films, giving rise to an obvious flexoelectric polarization and generating a significant photovoltaic effect in the LaFeO 3 -based heterostructures with nanosecond response under light illumination. This work not only demonstrates a novel self-powered photodetector different from the traditional interface-type structures, such as the p−n and Schottky junctions but also opens an avenue to design practical flexoelectric devices for nanoelectronics applications.

The structure and elemental distribution of PbZrO3 thin films are investigated. Defect controlled electrocaloric effects are discussed.

Environmentally benign Bi3.25La0.75Ti3O12 (BLTO) thin film capacitors were prepared by a cost effective chemical solution deposition method for high energy density storage device applications. Low annealing temperature annealed BLTO thin films showed very slim hysteresis loops with high maximum and small remnant polarization values. Increasing the applied electric field to 2040 kV/cm, the optimized BLTO thin films show a high recoverable energy density of 44.7 J/cm3 and an energy efficiency of 78.4% at room temperature. Additionally, the BLTO thin film capacitors exhibited excellent fatigue endurance after 4 × 108 cycles and a good thermal stability up to 140 °C, proving their strong potential for high energy density storage and conversion applications.

The energy storage performance of Ba2Bi4Ti5O18 thin film (left) and the atomic schematic structure of A2Bi4Ti5O18 (right).

Antiferroelectric thin films have demonstrated an excellent negative electrocaloric effect, and are potential candidates for future refrigeration applications.