(1 − x)(Bi1/2Na1/2)TiO3 − xBaTiO3 has been the most studied Pb-free piezoelectric material in the last decade; however, puzzles still remain about its phase transitions, especially around the important morphotropic phase boundary (MPB). By introducing the strain glass transition concept from the ferroelastic field, it was found that the phase transition from tetragonal (T, P4bm) to rhombohedral (R, R3c) was affected by a strain glass transition at higher temperature for x ≽ 4%. In these compositions, the T–R transition was delayed or even totally suppressed and displayed huge thermal hysteresis upon cooling and heating. Also, isothermal phase transitions were predicted and realized successfully in the crossover region, where the interaction between the T–R transition and the strain glass transition was strong. Our results revealed the strain glass nature in compositions around the MPB in this important material, and also provide new clues for understanding the transition complexity in other (Bi1/2Na1/2)TiO3-based Pb-free piezoelectric materials.
Ferroelectric transition involves tiny shift of ions within unit cell, thus being intrinsically a very fast process without apparent time-dependence. Contrary to this conventional wisdom, here we report a time-dependent ferroelectric transition, which occurs in hours. The system studied was Pb(1−x)(Zr0.4Ti0.6)(1−x/4)O3 − xLa system with relaxor-forming dopant La3+. The time-dependent ferroelectric transition occurs at the ferroelectric/relaxor crossover composition range of 0.09 < x ≤ 0.16. In these compositions, in situ Raman spectroscopy and transmission electron microscopy reveal very slow growth of ferroelectric phase. Dielectric measurement shows isothermal kinetics of the transition. The slow ferroelectric transition can be understood as being caused by the slowing-down of the otherwise fast growth of polar nano-domains due to the random local field caused by La3+, so that long time is needed to achieve long-range order macroscopic ferroelectric phase.
A device concept of an electrocaloric solid-state refrigeration is presented in this paper. The core component of the device is flexural mode composite actuators, each of which is comprised of an electrocaloric layer and an elastic substrate layer bonded together. The composite actuators have an electric field induced temperature change due to the electrocaloric effect and also have large electric field induced flexural deformation due to the converse piezoelectric effect, which enables the device to bend to contact with the heat source (or heat sink) for transferring heat. An analytical model is derived by considering multi-physical couplings for an edge-clamped circular composite device, which can accurately predict the temperature change of the device as compared with the indirect approach derived from the Maxwell relation. The model shows that the temperature change is a combinatorial result from the couplings of thermal, electric, and mechanical field in the device. Moreover, the model sheds light on exploring the optimization of the solid-state refrigeration device and indicates that different thickness ratios and radius ratios of the composite actuators have a large influence on the cooling performance of the refrigerator.
The translation of molecular‐scale chirality into macroscopic helical architectures is an intriguing scientific challenge capable of furthering our insight into the mechanism of biological chiral translation and the development of new materials. In this work, chiral induction and transfer through the bottom‐up self‐assembly of a chiral π‐electron donor template and an achiral π‐electron acceptor was employed to generate macroscopic enantiomerically pure helical fibers. The dynamic nature of these supramolecular helical fibers allowed for the efficient exchange of their chiral templates for achiral components, but were sufficiently robust enough to exhibit a chiral memory effect, retaining their helicity and enantiomeric purity during the exchange. More information can be found in the Communication by M. A. Olson, L. Fang, et al. on page 16553.
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