Tuesday, June 11, 2013

1306.1968 (Tran Doan Huan et al.)

Novel structural motif in low energy phases of NaSc(BH$_4$)$_4$    [PDF]

Tran Doan Huan, Maximilian Amsler, Silvana Botti, Miguel A. L. Marques, Stefan Goedecker
Sodium-scandium double-cation borohydride NaSc(BH$_4$)$_4$ experimentally crystallizes in the crystallographic space group $Cmcm$ where each sodium (scandium) atom is surrounded by six scandium (sodium) atoms. We carefully investigated this phase based on \textit{ab initio} calculations which indicate that the structure is dynamically unstable and gives rise to an energetically and dynamically more favorable phase with $C222_1$ symmetry and nearly identical x-ray diffraction pattern. By additionally performing extensive structural searches with the minima-hopping method we discovered a class of new low-energy structures exhibiting a novel structural motif in which each sodium (scandium) atom is surrounded by four scandium (sodium) atoms arranged at the corners of either a rectangle with nearly equal sides or a tetrahedron. These new phases are all predicted to be insulators with band gaps of 7.9-8.2 eV. Finally, we estimate the influence of these structures on the hydrogen-storage performance of NaSc(BH$_4$)$_4$.
View original: http://arxiv.org/abs/1306.1968

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