Yao Zhang,Chengpeng Hu,Yu Wang,Xiaolin Huang,Xuejie Sun,Mingxuan Liu,Bohan Xing,Xing Wen,Hao Tian
The improvement of piezoelectric properties is always a key issue in the study of piezoelectric materials. The construction of composition gradient (CG) is a novel method to improve piezoelectric properties. However, the physical mechanism of CG influence on the piezoelectric properties has to be analyzed further. We investigate the origin of the CG-affected piezoelectric property using a manganese-doped potassium sodium niobate single crystal (that is Mn: KNN) as a model system. The relationship between CG, microstructure and spontaneous polarization was explored by designing and growing Mn:KNN single crystals with different CGs. It is found that the built-in electric field (Ein) in single crystals is constructed by introducing the CG in the crystals. The large Ein induces a more ordered, large-sized striated domain structure. The Mn: KNN single crystal with a large CG has a uniform orientation of spontaneous polarization and large macro-piezoelectric properties (83 pC N−1). Therefore, it is important to explore the relationship between CG and the piezoelectric properties of single crystals in lead-free piezoelectric materials. The results can be used to further develop high-performance lead-free piezoelectric materials.
The heterogeneity of bones is elegantly adapted to the local strain environment, which is critical for maintaining mechanical functions. Such an adaptation enables the strong correlation between strain distributions and multiple gradients, underlying a promising pathway for creating complex gradient structures. However, this potential remains largely unexplored for the synthesis of functional gradient materials. In this work, heterogeneous bone-like nanocomposites with complex structural and compositional gradients comparable to bones are synthesized by inducing strain distributions within the polymer matrix containing amorphous calcium phosphate (ACP). Uniaxial stretching of composite films exerts the highest strain in the center, which ceases gradually toward the sides, resulting in the gradual decrease of polymer alignment and crystallinity. Simultaneously, the center with high orientation traps most ACP during stretching due to the nanoconfinement effect, which in turn promotes the formation of aligned nanofibrous structures. The sides experiencing the least strain have the smallest amounts of ACP, characteristic of porous architectures. Further crystallization of ACP produces oriented apatite nanorods in the center with a larger crystalline/amorphous ratio than the sides because of template-induced crystallization. The combination of structural and compositional gradients leads to gradient mechanical properties, and the gradient span and magnitude correlate nicely with strain distributions. Accompanying bone-like mechanical gradients, the center is less adhesive and self-healable than the sides, which allows a better recovery after a complete cutting. Our work may represent a general strategy for the synthesis of biomimetic materials with complex gradients thanks to the ubiquitous presence of strain distributions in load-bearing structures.
Yue Zhang,Qingguo Chi,Lizhu Liu,Tiandong Zhang,Changhai Zhang,Qingguo Chen,Xuan Wang,Qingquan Lei
The dielectric polymer-based films with excellent energy storage properties have been considered as potential candidates for flexible capacitors. In this study, the hierarchical gradient structures of the 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 nanofibers (BZCT NFs) are designed in the polyvinylidene fluoride (PVDF) composite films. The composite films with different compositions of BZCT NFs gradient structure were prepared by layer-by-layer electrospinning, hot-pressing, and quenching processes. The microstructures and electrical properties have been studied, and the results indicate that the BZCT NFs gradient structures can simultaneously improve the polarization and the breakdown strength of the PVDF-based composite films, leading to the enhancement of energy storage density (9.8 J/cm3) compared to that of pristine PVDF films (4.2 J/cm3). This work provides an efficient route to improve the energy storage properties of polymer-based composite films by structure modulation.
危险品化学品经营许可证（带存储）