A New hcp Phase Formed in the Ni-Nb System during Ion-beam-assisted Deposition

The NisoNb2o films were prepared by ion beam assisted deposition (IBAD)with various Ar ion energies. A phase evolution of fcc→amorphous→Ni Nb→Ni hcp was observed with the increasing of ion beam energy from 2 kev to 8 keV. When bombarded by Ar ions of 8 kev during deposition, a new crystalline phase with hcp structure was obtained, of which the lattice parameters are α=0.286 nm and c=0.483 nm, different from those of the similar A3B-type hcp phase previously reported. The experimental results were discussed in terms of thermodynamics and restricted kinetic conditions in the far-from-equilibrium process of IBAD. The formation of hcp phase may also be related to the valence electron effect.