Lu Shiyao,Wu Hu,Hou Jingwei,Liu Limin,Li Jiao,Harris Chris J.,Lao Cheng-Yen,Guo Yuzheng,Xi Kai,Ding Shujiang,Gao Guoxin,Cheetham Anthony K.,Kumar R. Vasant
Sodium-ion batteries (SIBs) are promising power sources due to the low cost and abundance of battery-grade sodium resources, while practical SIBs suffer from intrinsically sluggish diffusion kinetics and severe volume changes of electrode materials. Metal-organic framework (MOFs) derived carbonaceous metal compound offer promising applications in electrode materials due to their tailorable composition, nanostructure, chemical and physical properties. Here, we fabricated hierarchical MOF-derived carbonaceous nickel selenides with bi-phase composition for enhanced sodium storage capability. As MOF formation time increases, the pyrolyzed and selenized products gradually transform from a single-phase Ni 3 Se 4 into bi-phase NiSe x then single-phase NiSe 2 , with concomitant morphological evolution from solid spheres into hierarchical urchin-like yolk-shell structures. As SIBs anodes, bi-phase NiSe x @C/CNT-10h (10 h of hydrothermal synthesis time) exhibits a high specific capacity of 387.1 mAh/g at 0.1 A/g, long cycling stability of 306.3 mAh/g at a moderately high current density of 1 A/g after 2,000 cycles. Computational simulation further proves the lattice mismatch at the phase boundary facilitates more interstitial space for sodium storage. Our understanding of the phase boundary engineering of transformed MOFs and their morphological evolution is conducive to fabricate novel composites/hybrids for applications in batteries, catalysis, sensors, and environmental remediation.
Compositional fluctuation of the K and Na elements during the preparation process becomes a major issue for (K,Na)NbO 3 (KNN) lead-free ceramics to maintain relatively stable electrical properties. The raw material Bi 2 O 3 is more sensitive to high temperature. To improve electrical properties, it is more necessary to compensate the volatile Bi. In this work, the 0.96K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O 3 -0.04Bi 0.5*(1+ x ) Na 0.5 ZrO 3 ( x = −0.05, −0.02, 0.00, 0.02, 0.05, and 0.08) ceramics were selected as basis material. The excess Bi can increase the phase fraction of the T phase and decrease oxygen vacancy content, which effectively enhance the extrinsic contribution of the piezoelectric response. The electromechanical properties were optimized by excess Bi, and the optimal properties ( d 33 = 522 pC/N, k p = 58.9%, T c = 235 °C) were obtained in the ceramic with x = 0.05. The present work provides new guidelines for enhancing the piezoelectric performance of KNN ceramics by a simple method, which can be applied to other lead-free piezoelectric ceramic systems.
To meet the requirements of environmental friendliness, high-performance lead-free piezoelectric materials have become important materials for next-generation electronic devices. Here, lead-free and potassium-free NaNbO3 (NN)-based ceramics with high piezoelectric (d33 = 361 ± 10 pC/N) and dielectric (εr = 4500) properties were obtained by tolerant preparation techniques. The excellent piezoelectric and dielectric properties can be attributed to the relaxor morphotropic phase boundaries (R–MPB) and coexisting domain regions, which are beneficial in lowering the free energy and greatly improving the dielectric response and domain switching capability. Furthermore, the d33 of NaNbO3-10Ba(Ti0.7Sn0.3)O3-1.5NaSbO3 (NN-10BTS-1.5NS) ceramics can be maintained at 350 pC/N over the range of 25–80 °C with a change rate of less than 10%, exhibiting excellent temperature stability. Based on a series of in situ characterizations, the variations of the phase and domain structures of NN-based relaxor piezoelectric ceramics with temperature are clearly demonstrated. This work not only proposes new materials for sensors and actuators but also provides an excellent strategy for designing high-performance piezoelectric ceramics through phase and domain engineering.
危险品化学品经营许可证（带存储）