Biomass dielectric polymers hold promise in developing renewable and biodegradable capacitive energy storage devices. However, their typical discharged energy density remains relatively low (<20 J/cm³) compared to other existing synthetic polymers derived from petroleum sources. Here a greatly enhanced discharged energy density is reported in diluted cyanoethyl cellulose (CEC) nanocomposites with inclusion of ultralow loadings (0.3%, in volume) of 30 nm sized TiO₂ nanoparticles. Owing to the interfacial polarization introduced by interface, the composite of 0.3% exhibits a large dielectric constant of 29.2 at 1 kHz, which can be described by interphase dielectric model. Meanwhile, the introduction of nanofillers facilitate the formation of deeper traps impeding electrical conduction in CEC, which results in an ultrahigh breakdown strength of 732 MV/m. As a result, a remarkable discharged energy density of 12.7 J/cm³ with a charge-discharge efficiency above 90% is achieved, exceeding current ferroelectric-based and biomass-based nanocomposites. Our work opens a novel route for scalable biomass-based dielectrics with high energy storage properties.

The flexoelectric effect is a mechanical-electric coupling effect between strain gradient and electric polarization (i.e., positive flexoelectric effect) or electric field strength gradient and mechanical strain (i.e., converse flexoelectric effect). Unlike the piezoelectric effect, the flexoelectric effect, which is not limited by material symmetry and the Curie temperature, increases with decreasing the material size, thus attracting much attention and having a promising application. This review introduced the history of flexoelectric effect, measurement of flexoelectric coefficient, and mechanism to enhance flexoelectric effect. Recent studies on its application in the realm of sensors, actuators, mechanical memories, flexoelectric piezoelectric composites, energy harvesters, and electronic devices were highlighted. In addition, the further development of flexoelectric effect was also prospected.

Owing to the complex composition architecture of these solid solutions, some fundamental issues of the classical (1−x)Bi_1/2Na_1/2TiO-xBi_1/2K_1/2TiO₃ (BNT-xBKT) binary system, such as details of phase evolution and optimal Na/K ratio associated with the highest strain responses, remain unresolved. In this work, we systematically investigated the phase evolution of the BNT-xBKT binary solid solution with x ranging from 0.12 to 0.24 using not only routine X-ray diffraction and weak-signal dielectric characterization, but also temperature-dependent polarization versus electric field (P-E) and current versus electric field (I-E) curves. Our results indicate an optimal Na/K ratio of 81/19 based on high-field polarization and electrostrain characterizations. As the temperature increased above 100 °C, the x = 0.19 composition produces ultrahigh electrostrains (> 0.5%) with high thermal stability. The ultrahigh and stable electrostrains were primarily due to the combined effect of electric-field-induced relaxor-to-ferroelectric phase transition and ferroelectric-to-relaxor diffuse phase transition during heating. More specifically, we revealed the relationship between phase evolution and electrostrain responses based on the characteristic temperatures determined by both weak-field dielectric and high-field ferroelectric/electromechanical property characterizations. This work not only clarifies the phase evolution in BNT-xBKT binary solid solution, but also paves the way for future strain enhancement through doping strategies.

Low-temperature sintered (Na_1/2Bi_1/2)_0.935Ba_0.065Ti_0.975(Fe_1/2Nb_1/2)_0.025O₃ (NBT-BT-0.025FN) lead-free incipient piezoceramics were investigated using high-purity Li₂CO₃ as sintering aids. With the ≤0.5 wt% Li₂CO₃ addition, the introduced Li⁺ cations precede to enter the A-sites of the perovskite lattice to compensate for the A-site deficiencies. Once the addition exceeds 0.5 wt%, the excess Li⁺ cations will occupy B-sites and give rise to the generation of oxygen vacancies, which accelerate the mass transport and thus lower the sintering temperature effectively from 1100 ℃ down to 925 ℃. It was also found that a small amount of Li⁺ addition has little effect on the phase structure and electromechanical properties of the system, but overweight seriously disturbs these characteristics because of the large lattice distortion. The sintered NBT-BT-0.025FN incipient piezoceramics with 1.25 wt% Li₂CO₃ addition at 925 ℃ provides a large strain of 0.33% and a corresponding large signal piezoelectric coefficient d₃₃ of 550 pm/V at 60 kV/cm, indicating this system is a very promising candidate for lead-free co-fired multilayer actuator application.