A. Peles

First-principles study of the formation and migration of native defects in NaAlH4

We present a first-principles study of native defects in NaAlH4. Our analysis indicates that the structure and energetics of these defects can be interpreted in terms of elementary building blocks, which include V + AlH4, V − Na, V + H , H − i , and (H2)i. We also calculate migration barriers for several key defects, in order to compare enthalpies of diffusion to experimentally measured activation energies of desorption. From this, we estimate activation energies for diffusion of defects and defect pairs. We suggest that V + AlH4 and H − i , or V − Na and V + H , may be responsible for diffusion necessary for desorption. We discuss the possible role of V + H -H − i complex formation. The values we find are in the range of activation energies reported for catalyzed desorption. PACS numbers: 71.20.Ps, 61.50.Lt, 66.30.Lw Present address: United Technologies Research Center, 411 Silver Lane, MS 129-90, East Hartford, CT 06108 Corresponding author. E-mail: vandewalle@mrl.ucsb.edu