Intrinsic defects and dopants in LiNH2: a first-principles studyElectronic supplementary information (ESI) available: Defect formation energies at EFermi = 0 eV and proton migration path. See DOI: 10.1039/c0cp01540g

• Main Authors: Hazrati, E, Brocks, G, Buurman, B, de Groot, R. A, de Wijs, G. A
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c0cp01540g

The lithium amide (LiNH 2 ) + lithium hydride (LiH) system is one of the most attractive light-weight materials options for hydrogenstorage. Its dehydrogenation involves mass transport in the bulk (amide) crystal through lattice defects. We present a first-principles study of native point defects and dopants in LiNH 2 using density functional theory. We find that both Li-related defects (the positive interstitial Li + i and the negative vacancy V − Li ) and H-related defects (H + i and V − H ) are charged. Li-related defects are most abundant. Having diffusion barriers of 0.3-0.5 eV, they diffuse rapidly at moderate temperatures. V − H corresponds to the [NH] 2 − ion. It is the dominant species available for proton transport with a diffusion barrier of ∼0.7 eV. The equilibrium concentration of H + i , which corresponds to the NH 3 molecule, is negligible in bulk LiNH 2 . Dopants such as Ti and Sc do not affect the concentration of intrinsic defects, whereas Mg and Ca can alter it by a moderate amount. Ti and Mg are easily incorporated into the LiNH 2 lattice, which may affect the crystal morphology on the nano-scale. Formation energies of intrinsic defects in LiNH 2 , their mobility, and effects of dopants (Mg, Ca, Sc, Ti) are studied, here illustrated with hopping of a proton interstitial.