Structural phase transition in the Hf–Ni system studied by ab initio calculation and ion beam mixing

Hafnium films with the respective thicknesses of 100, 200, 300, 400 Å were examined by transmission electron microscopy and were shown to deposit with an hcp structure, then transformed into an fcc structure after being irradiated by 200 KeV xenon ions at 77 K. The first principles calculation showed the cohesive energies per atom of the hcp and fcc structures of Hf were extremely close, which was probably responsible for the observed hcp-to-fcc structural transition upon irradiation. Meanwhile, a deposited Hf–Ni–Hf sandwich-structured film with an overall composition around Ni25Hf75 was identified to consist of two fcc structures and later transformed into a uniform fcc structure upon irradiation, which is also confirmed by ab initio calculation that the fcc-type (L12) crystalline phase was more likely to be formed than the hcp-type for a possible Hf-rich Ni25Hf75 alloy.