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Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZ) ceramics, one of the lead-free pizoelectric materials, were focused due to the environmental concern against lead. A modified BCTZ powder sol-gel fabrication process was experimentally introduced with the addition of glycerol, in order to provide an effective approach to optimize the piezoelectric response of BCTZ ceramics. The results showed that the piezoelectric properties enhanced in terms of the piezoelectric coefficient of d33, 510 pC/N and the electromechanical coupling coefficient of kp, 0.501. The enhancement in electrical properties, such as dielectric, ferroelectric and piezoelectric, could be related to the homogenous microstructure and larger grain size of BCTZ ceramic powders after the introduction of glycerol during the modified sol-gel strategy.

In order to develop the application of energy storage ceramics, the dielectric properties and energy storage density of Ba0.1Sr0.9Zr0.18Ti0.82O3 ceramics (BSZT-118) prepared by the modified sol–gel process were researched under different temperatures under electric field. The results show that the dielectric constant of BSZT-118 is consistent with Johnson’s formula based on Devonshire phenomenological theory, and the anharmonic constant (α) increases as the temperature rises. The energy storage density of BSZT-118 is influenced by the electric field and temperature. With the increase in temperature, the storage density of BSZT decreases and the fluctuation of storage density increases under electric field. The conduction mechanism of BSZT-118 is mainly space charge-limited conduction (SCLC) below 60 °C, and it is mainly Ohmic conduction above 60 °C.

Piezoelectricity—the direct interconversion between mechanical and electrical energies—is usually remarkably enhanced at the morphotropic phase boundary of ferroelectric materials1–4, which marks a transition region in the phase diagram of piezoelectric materials and bridges two competing phases with distinct symmetries1,5. Such enhancement has enabled the recent development of various lead and lead-free piezoelectric perovskites with outstanding piezoelectric properties for use in actuators, transducers, sensors and energy-harvesting applications5–8. However, the morphotropic phase boundary has never been observed in organic materials, and the absence of effective approaches to improving the intrinsic piezoelectric responses of polymers9,10 considerably hampers their application to flexible, wearable and biocompatible devices. Here we report stereochemically induced behaviour in ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) copolymers, which is similar to that observed at morphotropic phase boundaries in perovskites. We reveal that compositionally tailored tacticity (the stereochemical arrangement of chiral centres related to the TrFE monomers11,12) can lead to intramolecular order-to-disorder evolution in the crystalline phase and thus to an intermediate transition region that is reminiscent of the morphotropic phase boundary, where competing ferroelectric and relaxor properties appear simultaneously. Our first-principles calculations confirm the crucial role of chain tacticity in driving the formation of this transition region via structural competition between the trans-planar and 3/1-helical phases. We show that the P(VDF-TrFE) copolymer with the morphotropic composition exhibits a longitudinal piezoelectric coefficient of −63.5 picocoulombs per newton, outperforming state-of-the-art piezoelectric polymers10. Given the flexibility in the molecular design and synthesis of organic ferroelectric materials, this work opens up the way for the development of scalable, high-performance piezoelectric polymers.

In electrocaloric active polymers, the ferroelectric copolymer P(VDF-TrFE) 65/35 mol% exhibits the largest caloric performance (, at an electric field of 100 MV m−1 and 85 °C) due to a sharp first-order phase transition. However, this high property occurs only at the first cycle and then drops significantly in the following electrical cycle, which significantly limits the promising applications of these copolymers. Here we use a blend approach to solve the irreversibility issue. We show that the incorporation of a terpolymer into a copolymer results in the evolution from normal ferroelectric to relaxor, which is accompanied by a large reduction in the thermal hysteresis. As a result, we find that complete reversibility of electrocaloric cycles in blends can be achieved for the copolymer/terpolymer volume ratio as 3/7.

We study the electrocaloric effect in the composites composed of the ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer matrix and lead-free BaZr0.2Ti0.8O3 (BZT) fillers. The P(VDF-TrFE-CFE)/BZT composite with 5 vol. % BZT exhibits a high adiabatic temperature change of ΔT = 7.4 K and a large isothermal entropy change of ΔS = 30 J kg−1 K−1 under an electric field of 90 MV m−1 at room temperature. The electrocaloric response in the composites is significantly enhanced when compared to those of the constituent components, which has been attributed to the polymer-filler interfacial coupling effect. In addition, the composites display a wide operational temperature window as a result of their ferroelectric relaxor nature.