Juan Salvador Arellano Peraza

1. Juan Salvador Arellano Peraza Área de Física Atómica Molecular Aplicada, Universidad Autónoma Metropolitana Azcapotzalco, C.P. 02200, México D.F., México Motivation * Graphene, has been obtained (year 2004). This is a 2D and only one atom thick material. It can be converted to 0D buckyballas, 1D nanotubes or stacked in the best known 3D graphite. See Figure 1. * Graphite is formed by weakly interacting parallel planar carbon layers. Atoms and molecules can be intercalated between those layers giving rise to a variety of intercalated compounds. It is the richest Li compound existing at normal pressure Stage-1 compound AA stacking of the graphene layers The Li atoms are placed midway between two parallel hexagons, above the center of the hexagon Only one third of those positions are occupied by Li LiC6 LiC2 LiC3 Pb difussion along the /6,6) carbon nanotube This compound forms only by high pressure synthesis Experimental phase: AA stacking of the graphene layers The Li atoms are placed midway between two parallel hexagons, above the center of the hexagon Conclusions circles: AA stacking stars: AB stacking circles: AA stacking stars: AB stacking ÑLi midway between graphene layers ÑLi up and down the middle Ñrelaxed Li positions From Graphite to carbon nanotubes. A guide for its applications on nanoscience and nanotechnology 2mev/atom: energy difference between graphite and graphene AB stacking, is the most abundant form of graphite (circles) AA stacking (two adjacent graphene layers), present in the intercalated compounds (triangles) rDensity Functional Formalism: FHI96MD code rExchange-Correlation functional: Local Density Approximation rNonlocal norm-conserving pseudopotential of Hamman et al. for Carbon (4 valence electrons) rAll electron description of Lithium for all the lithium intercalated compounds. [3] [3] Figure 1 [1] Figure 2 [2] Hydrogen molecule adsorption on nanotube [2] [3] Superdense compound formed by ball-milling; it is stable under ambient pressure The X-ray diffraction pattern indicates Li atoms at ± 0.83 au from the medium plane between the graphene layers Pb atom adsorption on a graphene layer. The figure shows there are 8 carbon atoms per one Pb atom. The atom is adsorbed at a distance of 4.8 a.u., a little less than the equilibrium distance for the hydrogen molecule above the graphene layer, 5.07 a.u. These result was reported on reference [4]. The binding energy for the Pb atom on the (6,6) carbon nanotube axis is 0.27 eV. The initial calculations for the difussion of the Pb atom along the carbon nanotube axis shows that this could be and easy process, that is, without barrier energies. rAdequate description of graphite (AB packing, cohesion, compressibility) by DFT-LDA calculations rLi intercalation changes the stacking of C layers from AB in graphite to AA in Li compounds rThe distance between graphene layers increases and the uniaxial compressibility decreases in LiC6 with respect to pure graphite rDFT underestmates the expansion of the lattice and the uniaxial compressibility of LiC2 as compared to the experimental values. Assuming AB stacking, we recover the experimental expansion of the lattice but the value of the uniaxial compressibility is similar (small) to that obtained with AA stacking rDFT calculations do not predict separation of the Li atoms from the medium plane between graphene layers in the LiC3 compounds rIt has been given a brief scope of the possible applications of the graphene, graphite and carbonaceous materials as can be the design of new lithium batteries or the hydrogen storage. ¡There are many more applications under development! [1] A. K. Geim and K.S. Novoselov. Nature materials, Vol. 6, March 2007, p. 183. [2] J. S. Arellano, L.M. Molina, A. Rubio, M.J. López and J. A. Alonso. J. Chem. Phys. Vol. 117, No. 5, 1 August 2002, p. 2281-2288. [3] Juan Salvador Arellano Peraza, L. M. Molina, M. J. López, A. Rubio y J. A.. Alonso. “Resultados para litio intercalado en grafito, LiC2 y LiC6 usando teoría de funcionaled de la densidad”. Memoria de la XIV Semana de la Docencia e Investigación en Química. Universidad Autónoma Metropolitana-Azcapotzalco, año 2001,p.113-123. [4] J. S. Arellano, L.M. Molina, A. Rubio, and J. A. Alonso. J. Chem. Phys. Vol. 112, Number 18, 8 May 2000, p. 8114-8119.