Settem Manoj, Srivastav Ajeet K, Kanjarla Anand K
Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai, 600036, India.
Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of Technology, Nagpur, 440010, India.
Phys Chem Chem Phys. 2021 Dec 1;23(46):26165-26177. doi: 10.1039/d1cp04145b.
The structure of octahedral Ag-Cu nanoalloys is investigated by means of basin hopping Monte Carlo (BHMC) searches involving the optimization of shape and chemical ordering. Due to the significant size mismatch between Ag and Cu, the misfit strain plays a key role in determining the structure of Ag-Cu nanoalloys. At all the compositions, segregated chemical ordering is observed. However, the shape of the Cu nanocrystal and the associated defects are significantly different. At lower amounts of Cu (as little as 2 atom %), defects close to the surface are observed leading to a highly non-compact shape of the Cu nanocrystal which is non-trivial. The number of Cu-Cu bonds is relatively lower in the non-compact shape which is contrary to the preference of bulk Ag-Cu alloys to maximize the homo-atomic bonds. Due to the non-compact shape, {100} Ag-Cu interfaces are observed which are not expected. As the amount of Cu increases, the Cu nanocrystal undergoes a shape transition from non-compact to a compact octahedron. The associated defect structure is also modified. The structural changes due to the strain effects have been explained by calculating the atomic pressure maps and the bond length distributions. The trends relating to the structure have also been verified at larger sizes.
通过涉及形状优化和化学有序化的盆地跳跃蒙特卡罗（BHMC）搜索，研究了八面体Ag-Cu纳米合金的结构。由于Ag和Cu之间存在显著的尺寸失配，失配应变在决定Ag-Cu纳米合金的结构中起着关键作用。在所有成分中，均观察到化学有序化的偏析。然而，Cu纳米晶体的形状和相关缺陷却有显著差异。在较低的Cu含量下（低至2原子%），观察到靠近表面的缺陷，导致Cu纳米晶体呈现高度非紧凑的形状，这一现象并不简单。在非紧凑形状中，Cu-Cu键的数量相对较少，这与块状Ag-Cu合金倾向于最大化同原子键的情况相反。由于形状非紧凑，观察到了意想不到的{100} Ag-Cu界面。随着Cu含量的增加，Cu纳米晶体经历了从非紧凑到紧凑八面体的形状转变。相关的缺陷结构也发生了改变。通过计算原子压力图和键长分布，解释了应变效应引起的结构变化。在更大尺寸下，与结构相关的趋势也得到了验证。
