Diffusion of hydrogen vacancy in Na3AlH6

We perform first-principles calculations to investigate neutral and charged H vacancies dynamics involving vacancy formation and diffusion in Na3AlH6. We find that the activation barrier for local diffusion (diffusion within AlH5 unit) is smaller than that of nonlocal diffusion (diffusion between AlH6 and AlH5 units) for all types of H vacancies; H diffusion in Na3AlH6 is dominated by mobility of positively charged H vacancies. Furthermore, our results confirm that the observed highly mobile species by anelastic spectroscopy measurements is probably the positively charged H vacancies in the form of local diffusion. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3225152]