Effects of Ni doping on various properties of NbH phases: A first-principles investigation

Changes in the stability, hydrogen diffusion, and mechanical properties of the NbH phases from Ni-doping was studied by using first-principles methods. The calculation results reveal that the single H atom adsorption is energetically favorable at the tetrahedral interstitial site (TIS) and octahedral interstitial site (OIS). The preferred path of H diffusion is TIS-to-TIS, followed by TIS-to-OIS in both Nb₁₆H and Nb₁₅NiH. Ni-doping in the Nb₁₅NiH alloy lowers the energy barrier of H diffusion, enhances the H-diffusion coefficient (D) and mechanical properties of the Nb₁₆H phase. The value of D increases with increasing temperature, and this trend due to Ni doping clearly becomes weaker at higher temperatures. At the typical operating temperature of 400 K, the D value of Nb₁₅NiH (TIS) is about 1.90 × 10^-8 m²/s, which is about 80 times higher than that of Nb₁₆H (TIS) (2.15 × 10^-10 m²/s). Our calculations indicated that Ni-doping can greatly improve the diffusion of H in Nb.