Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
Nano Lett. 2022 Jun 8;22(11):4333-4339. doi: 10.1021/acs.nanolett.2c00411. Epub 2022 May 18.
Achieving metal nanocrystals with metastable phase draws much attention due to their anticipated fascinating properties, wheras it is still challenging because their polymorphism nature and phase transition mechanism remain elusive. Here, phase stability of face-centered cubic (fcc) Pd nanocrystals was studied via spherical aberration (Cs)-corrected transmission electron microscopy (TEM). By constructing a well-defined Pd/C composite structure, Pd nanocrystals encapsulated by graphite, the dispersion process of fcc Pd was observed through a nucleation and growth process. Interestingly, Cs-corrected scanning TEM analysis demonstrated that the newly formed Pd nanocrystals could adopt a metastable hexagonal phase, which was considered challenging to obtain. Accordingly, formation mechanism of the hexagonal Pd nanocrystals was proposed, which involved the combined effect of two factors: (1) templating of graphite and (2) size effect. This work is expected to offer new insight into the polymorphism of Pd nanocrystals and pave the way for the future design of metastable metal nanomaterials.
由于具有预期的迷人性质，具有亚稳相的金属纳米晶体引起了广泛关注，然而，由于其多晶型性质和相变机制仍然难以捉摸，因此仍然具有挑战性。在这里，通过球差校正透射电子显微镜 (TEM) 研究了面心立方 (fcc) Pd 纳米晶体的相稳定性。通过构建定义明确的 Pd/C 复合材料结构，石墨包裹的 Pd 纳米晶体，通过成核和生长过程观察到 fcc Pd 的分散过程。有趣的是，Cs 校正扫描 TEM 分析表明，新形成的 Pd 纳米晶体可以采用亚稳的六方相，这被认为难以获得。因此，提出了六方 Pd 纳米晶体的形成机制，该机制涉及两个因素的共同作用：（1）石墨的模板作用和（2）尺寸效应。这项工作有望为 Pd 纳米晶体的多晶型性提供新的见解，并为未来设计亚稳金属纳米材料铺平道路。
