Shape change of submicron nickel particles under hydrogen and nickel chloride vapor

The shape of Ni particles is important. A spherical shape is favored for an electrode material in multilayer ceramic capacitor (MLCC) due to high packing density. A cubic shape is better for applications in catalysts and bioseparation due to its higher magnetic property than a spherical shape. It was found that cubic Ni particles which has a face-centered cubic (fcc) crystal structure, can be synthesized by chemical vapor synthesis (CVS). In this study, to examine whether the cubic shape of Ni particles synthesized by CVS is the growth or the equilibrium shape, the shape change of Ni particles by annealing under H₂ and NiCl₂ atmospheres was observed. It was confirmed by a density function theory (DFT) method that H₂ and NiCl₂ vapor favor respectively spherical and cubic shapes, which indicates that NiCl₂ stabilizes the {1 0 0} faces of Ni. In this computational work, we provide gas adsorption energies and relaxed atomic structures of Ni(1 0 0) and Ni(1 1 1) surface models. Using this fact, suitable synthetic conditions for cubic and spherical Ni particles could be derived. It was confirmed that the high and low reduction rate favor respectively spherical and cubic shapes during CVS.