X-ray powder diffraction study of amorphous-to-crystalline phase transition in Ni

Systematic data on the amorphous–crystalline transition in Ni have been obtained by high-temperature X-ray diffraction analysis. It is established that the amorphous structure of Ni nanoparticles is stable up to 200$^\circ$C. Ni nanocrystals, which have coherent-scattering regions (CSRs) 5–15 nm in size (depending on the isothermal annealing temperature) are formed in the temperature range of 300–600$^\circ$C. The activation energy of nanocrystal growth has been estimated to be 67.3 kJ/mol. The dependence of the unit-cell parameter of nanocrystalline Ni on the CSR size is determined. An increase in the lattice constant is observed with an increase in CSR in nanocrystalline Ni particles.