Size-induced structural phase transition at ~6.0 nm from mixed fcc-hcp to purely fcc structure in monodispersed nickel nanoparticles

摘要

We have investigated the core issue of atomic lattices in monodispersed Ninanoparticles (NPs) of sizes 3.8 nm to 10.1 nm using detailed analysis of X-raydiffraction, synchrotron radiation X-ray absorption spectroscopy (XAS) andmagnetization data. This has revealed the very remarkable coexistence of atomicface-centered cubic (fcc) and hexagonal closed-packed (hcp) lattices in sampleswith particle size less than or equal to 6.0 nm with the prevalence of only fccphase beyond this. They are also associated with reduced coordination number,modified electronic structure, and surface atom coordination with ligands.Magnetization data furthermore reveal coexistence of ferromagnetism andsuperparamagnetism at 300 K. Considered to be due to dominant roles of ligands,they are likely to open up far-reaching implications to their futureapplications.