First direct evidence of size-dependent structural transition in nanosized nickel particles

Templated Growth of Hexagonal Nickel Carbide Nanocrystals on Vertically Aligned Carbon Nanotubes

“…Figure 2c shows a relatively large Ni nanocrystal (∼20 nm) on the CNT surface exhibiting a hexagonal structure as revealed by the corresponding [12 j 13 j ] zone axis in SAD pattern (inset in Figure 2c). The evidence of a hexagonal structure in this relatively large nanocrystal contradicts the critical size (∼4 nm) of the FCC-HCP transition reported previously for Ni nanocrystals by Illy et al 9 Parts a and b of Figure 3 are respectively SEM images showing the lift-out procedure and the sample prepared for 3DAP studies of the Ni nanocrystals deposited on the carbon nanotubes. The lifted-out sample was attached on a Si micropillar and then subsequently milled using the Ga ion beam with a final tip radius less than 30 nm, as shown in Figure 3b.…”

“…12 These synthesis methods indicate that HCP nickel is only observed below a certain critical crystallite size (∼4 nm) and changes to the equilibrium FCC structure for larger crystalline sizes. 9,10 Nickel does not form a carbide under equilibrium conditions; however, there have been reports of metastable nickel carbides (Ni 3 C) forming as a result of mechanical alloying in high-energy ball-milled mixtures. 12 These nickel carbide (Ni 3 C) nanocrystals also exhibited a highly disordered and defective internal structure due to extreme local pressures and temperatures involved in far-from equilibrium processing, such as high-energy ball milling.…”

“…Interestingly, there have been reports in the literature related to the stabilization of a nonequilibrium hexagonal structure (hexagonal closepacked or HCP) in nanostructured forms of nickel, including HCP metastable nickel carbide nanocrystals. [9][10][11][12] The HCP phase is typically observed in case of far-from-equilibrium synthesis routes such as wet chemical synthesis at very low temperatures when the nanocrystals grow from an amorphous phase, 9 decomposition of neutral metal complex, 10 thin film processing via heteroepitaxial growth, 11 and mechanical alloying via highenergy ball milling. 12 These synthesis methods indicate that HCP nickel is only observed below a certain critical crystallite size (∼4 nm) and changes to the equilibrium FCC structure for larger crystalline sizes.…”

Structure of nickel nanoparticles in a microcrystalline cellulose matrix studied using anomalous small-angle X-ray scattering

“…Recently, nickel nanoparticles have been the topic of a number of studies owing to their applications as catalysts and magnetic materials. Metallic nickel as well as nickel oxide, boride and phosphide nanoparticles have been prepared (Illy et al, 1999;Xie et al, 2005). In many studies the nanoparticles have been self-supported (LesliePelecky & Rieke, 1996), but also nanocomposite materials where the nanoparticles are in e.g.…”

Continuous-Flow Synthesis of Ni(0) Nanoparticles Using a Cone Channel Nozzle or a Micro Coaxial-Injection Mixer

“…Mainly two types of chemical processes are in use: polyol-process [7][8][9][10] and the reduction with strong reducing compounds like hydrazine [11] or borhydride [12,13]. Chemical reduction is the method of choice for producing nonagglomerated nickel particles due to the possibility to control particle size and morphology by changing reactant and surfactant concentration, pH-value, or temperature [14][15][16][17][18][19][20].…”