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摘要
Platinum-based nanoclusters have been widely studied because of the possibility to tune the physical and chemical properties as a function of shape, size, chemical composition, and so forth. Although the Pt composition can be experimentally controllable, the location of the Pt species is a challenge as several physical parameters might play a role, for example, surface energy, segregation energy, atomic radius, charge transfer, strain, and so forth. Here, we report density functional theory calculations for 55-atom PtnTM55-n (TM = Y, Zr, Nb, Mo, and Tc) nanoalloys, which provides new insights. In general, the replacement of TM by Pt atoms increases the relative stability of the nanoalloys, and the maximum stability is reached at Pt-rich compositions (n = 35-42). From our analysis, an increase in the number of heterobonds maximizes the charge transfer among the Pt-TM species, and its magnitude depends on the electronegativity difference, coordination, and location (core or surface) of both species. For most cases, there is an electron density flow from the core to the surface region, and hence, the core is cationic, whereas the surface is anionic; however, there are few exceptions, in particular, for PtY. Thus, it yields an attractive Coulomb interaction among the chemical species and minimizes the total energy. For PtTM in which Pt is slightly larger or has a similar size as the TM atoms (Tc, Mo, and Nb), Pt atoms prefer the surface sites (smaller species are located on the core), which helps to release the strain energy. However, the charge transfer from TM to Pt helps to increase the attractive interaction between the surface and core, increasing the pressure on the core region. For PtTM in which TM (Zr and Y) is larger than Pt, contrary to what would be expected, there are some Pt atoms in the core region (including at the geometric center), resulting in a cationic surface. The release of the strain energy is obtained by symmetry breaking.
- 出版日期2018-4-5
