Wen Yu-Hua, Li Ya-Meng, Yang Wei-Hua, Huang Kai-Wen, Huang Rao
Department of Physics, Xiamen University, Xiamen 361005, China.
Nanoscale. 2022 Jul 21;14(28):10236-10244. doi: 10.1039/d2nr01974d.
A crystal phase is a key factor to determine the physical and chemical properties of crystalline materials. As a new class of nanoscale structures, heterophase nanoparticles, which assemble conventional and unconventional phases, exhibit exceptional properties in comparison with their single-phase counterparts. In this work, we explored the thermodynamic stability of Au, Co, and AuCo heterophase nanoparticles with fcc and hcp phases by using molecular dynamics simulations. These heterostructured nanoparticles were continuously heated to examine their thermally activated structural evolutions. Au and Co single-phase nanoparticles were also considered for comparison. The results show that the phase transition between fcc and hcp is absent in these heterophase nanoparticles despite the existence of an unconventional phase. Although the melting of Au and Co heterophase nanoparticles is homogeneous, AuCo heterophase nanoparticles show heterogeneous melting, , the Au fcc domain firstly melts, followed by the melting of the Co hcp domain, exhibiting a typical two-stage melting characteristic and resulting in the existence of a solid-core/liquid-shell structure within a considerable temperature region. Furthermore, the mutual diffusion of atoms between fcc and hcp domains is observed in the Au and Co heterophase nanoparticles. However, the unidirectional diffusion from the Au domain to the Co domain is found in the AuCo heterophase nanoparticles prior to their overall melting. This study deepens the fundamental understanding of the thermodynamic evolution of metallic heterogeneous nanoparticles and provides mechanistic and quantitative guidance for the rational design and applications of nanoscale multiphase heterostructures.
晶相是决定晶体材料物理和化学性质的关键因素。作为一类新型的纳米级结构，由常规相和非常规相组装而成的异相纳米颗粒与其单相对应物相比具有特殊性能。在这项工作中，我们通过分子动力学模拟研究了具有面心立方（fcc）相和六方密排（hcp）相的金、钴和金钴异相纳米颗粒的热力学稳定性。这些异质结构纳米颗粒被持续加热以研究其热激活结构演变。还考虑了金和钴单相纳米颗粒用于比较。结果表明，尽管存在非常规相，但这些异相纳米颗粒中不存在fcc相和hcp相之间的相变。虽然金和钴异相纳米颗粒的熔化是均匀的，但金钴异相纳米颗粒呈现非均匀熔化，即金的fcc域首先熔化，随后是钴的hcp域熔化，呈现典型的两阶段熔化特征，并在相当大的温度区域内导致固核/液壳结构的存在。此外，在金和钴异相纳米颗粒中观察到fcc域和hcp域之间原子的相互扩散。然而，在金钴异相纳米颗粒整体熔化之前，发现从金域到钴域的单向扩散。这项研究加深了对金属异质纳米颗粒热力学演变的基本理解，并为纳米级多相异质结构的合理设计和应用提供了机理和定量指导。
