Preparation and characterization of hexagonal close-packed Ni nanoparticles

Abstract

Hexagonal close-packed Ni nanoparticles were synthesized using a heat-treating technique with the precursors prepared by the sol-gel method. The synthesis condition, structure, and morphology of the samples were characterized and analysed by thermogravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicate that the hexagonal close packed Ni nanoparticles were synthesized at a heat-treating temperature of 300uC. The cell constants are calculated at a 5 0.2652 nm and c 5 0.4334 nm. The average grain size of the hexagonal close-packed Ni particles evaluated by Scherrer equation is about 12 nm. The phase transformation from a hexagonal close-packed Ni to a face-centered cubic Ni structure occurred when the heat-treating temperature was increased.

Size-Induced Structural Phase Transition at ∼6.0 nm from Mixed fcc–hcp to Purely fcc Structure in Monodispersed Nickel Nanoparticles

“…Intriguingly, when the particle size is reduced to 3.8 nm, a single peak near 44.5 o could be due to either hexagonal closed-packed Ni (011) and fcc Ni (111) peaks together or separately as they are close to 44.5 o . This conjecture is in line with the probability to form hcp on/ near the surface of the particle and/ or the whole of the NPs when all the unit cells lie on the surface only, as hcp phase being less stable thermodynamically than fcc phase [24]. Since they may not be necessarily intermixed, Ni NPs might have a possible formation of its comparatively less stable hcp structure at/ near the surface or the outer shell, and more stable fcc structure at the core.…”

Mechanism of polyol assisted ccp to hcp crystal phase conversion of nickel particles

“…The latter forms only within a specic temperature range (200-325 C). 31 Once hcp-Ni is formed, it is stable at temperatures below 325 C but reverts back to ccp when the temperature is increased above 360 C. [30][31][32] Considering the metastable nature of the hcp phase, it is difficult to obtain by fast growth techniques (i.e. CVD, spray pyrolysis) Ni particles having a well-dened and controllable ccp/hcp ratio.…”

“…Polyols have been the preferred dispersion media for such studies. 31 In their work, Tzitzios et al 35 suggested that polyols with a higher molecular weight have elevated boiling points and are more effective in converting the Ni to an hcp structure. In this view, the temperature appears to be the only important process parameter.…”

“…29 At temperatures in the 200-360 C range, however, it can be converted to an antiferromagnetic hcp form. [30][31][32] This has brought attention to the synthesis and characterization of hcp Ni particles because of their unique properties emanating from size, crystal structure, and mutual interactions. 29,30,[33][34][35] To date, Ni particles with various sizes and shapes have been prepared by chemical reduction, sputtering, 36 thermal processes, 32,37,38 reverse microemulsion technique, 39 and polyol mediated processes.…”

Universal Stability and Temperature Dependent Phase Transformation in Group VIIIB–IB Transition Metal FCC Nanowires

“…In recent years, HCP nanoparticles have been prepared and characterized using various experimental techniques, i.e., thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), atomic force microscopy (AFM), X-ray diffraction (XRD), etc . For example, hexagonal-close-packed Ni nanoparticles were synthesized using a heat-treating technique with the precursors prepared by the sol–gel method . The phase transformation from a hexagonal-close-packed Ni to a face-centered-cubic Ni structure occurred when the heat-treating temperature was increased.…”