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Venkataramanan N.S.,Institute for Materials Research IMR | Sahara R.,Institute for Materials Research IMR | Mizuseki H.,Institute for Materials Research IMR | Kawazoe Y.,Institute for Materials Research IMR
Journal of Physical Chemistry A | Year: 2010

Using the first principles method, we study the growth behavior and electronic and magnetic properties of TiNin (n = 1-12) clusters to clarify the effect of Ti modulation on the nickel nanostructures. Furthermore, chemisorption of H2 was studied to understand the chemical reactivity of H2 on the small Ni- and Ti-doped Ni clusters. The calculations are performed using the plane wave pseudopotential approach under the density functional theory and generalized gradient approximation for the exchange and correlation functional. The optimized geometries of TiNin-1 clusters indicate that the substitution of Ti brings a substantial structural reconstruction from 3D structure to a layer structure in which Ti atom is found to coordinate with Ni atoms to a maximum extent. This is accompanied by a significant enhancement in binding energies and reduction in chemical reactivity. Furthermore, the magnetic moments of the small Ti-doped Ni clusters are quenched because of the antiferromagnetic alignment of the Ti electrons. The lowest-energy structure of H2 chemisorbed on Ni clusters shows that hydrogen prefers to adsorb on the edge site with two hydrogen atoms on these clusters in neighboring sites as the preferred arrangement. The incorporation of Ti atom improves the chemisorption energy of Ni clusters. Bader charge analysis indicates that with the formation of metal hydride, the H atoms withdraw charges from the metal centers, making them lose an electron, and carry a positive charge over them. Furthermore, Ti doping is found to enhance the chemical reactivity of Ni clusters. © 2010 American Chemical Society.

Souissi M.,Institute for Materials Research IMR | Belosludov R.V.,Institute for Materials Research IMR | Subbotin O.S.,RAS Nikolaev Institute of Inorganic Chemistry | Mizuseki H.,Institute for Materials Research IMR | And 2 more authors.
Journal of Inclusion Phenomena and Macrocyclic Chemistry | Year: 2011

The thermodynamic properties of propane clathrate hydrate with cubic structure IV were studied using a method based on the solid solution theory of van der Waals and Platteeuw but allows one to take into account the influence of guest molecules on the host lattice and guest-guest interactions. The free energies, equations of state, and chemical potentials of this hydrate were estimated using this approach. The proposed theory was used for construction of "guest gas-hydrate-ice I h " equilibrium curves of propane hydrates. It was found that the water framework of structure IV was dynamically stable and that the fully C3H8 filled structure was thermodynamically stable in the region of pressure from 43 to 50 MPa as compared with the hexagonal ice. The formation pressure of propane hydrate with structure IV is higher than that of propane hydrate with cubic structure II. However, a structural transformation from structure II to IV of propane hydrate was estimated under a pressure of 78 MPa at 290 K. © 2010 Springer Science+Business Media B.V.

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