Investigation of the lattice expansion for Ni nanoparticles

Nickel nanoparticles with various grain sizes were successfully prepared by anodic arc discharge plasma method. The samples prepared by this method were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and the corresponding selected-area electron diffraction (SAED) to determine the crystal structure, lattice parameter, morphology and particle size. The experiment results indicate that the crystal structure of the samples is FCC structure as same as the bulk materials. The lattice parameters for Ni nanoparticles are always larger than the equilibrium values of the perfect single crystal lattice respectively, the lattice parameter increase significantly with the decrease of the grain size, the lattice expansion was found, and the expansion quantity of the lattice parameter is in direct proportion to the reciprocal of grain size. The values of the unit cell volume increase remarkably with the decrease of the grain size. The lattice expansion is the result of the interfacial energy and surface tension mutual attraction of Ni nanoparticles, this phenomenon can be explained according to the thermodynamic theory.