For the samples prepared at 400°C, the phase percentages obtained by the whole-profile fitting program are shown in Table 1. Following this preparation method, different Ni phase percentages can be easily controlled by the calcination time. As can be seen in Table 1, while the hcp Ni phase percentage decreases with increasing of the calcination time, the fcc Ni phase increases. It means that during the calcination the hcp phase is transformed to fcc phase and the number of fcc Ni nanoparticles is increased. A long calcination time is needed in order to obtain Ni/NiO nanoparticles.