Structural stability and hydrogen diffusion in alloys

Structural stability and hydrogen diffusion in TiHx alloys, with x = 0 – 2 , have been studied by ab initio total energy calculations. A concentration dependent structural transformation is predicted to occur from FCC ( x ≤ 0.5 ) to FCT ( 0.75 ≤ x ≤ 1.50 ) and then again to FCC ( 1.75 ≤ x ≤ 2.0 ) . Moreover, a concentration independent hydrogen diffusion behavior is found with activation energies of 0.50 eV in TiH0.75 (along the [110] direction) and 0.54 eV in TiH1.75 (along the [100] direction), respectively. These results are in good agreement with the recent experimental works.