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We studied the energetics and structure of simple point defects and defect clusters in the Ni-Al system. Atomistic computer simulation was used for this purpose with embedded atom interatomic potentials. In both, NisAl and NiAl the energetics are such that excess Ni is accommodated by anitisite defects more easily than excess Al. Structural vacancies are therefore more likely with stoichiometry deviations in the Al-rich side than in the Ni-rich side. The interaction of vacancies of different types to form divacancies was studied. Several configurations were found with a very similar energy to that of the two monovacancies far apart. Some configurations show attraction and others show repulsion. The vacancy interaction distance is limited to a few interatomic distances.The relaxation around these defects was studied in detail and the results can be interpreted in terms of the larger size of the Al atom.

Dye-sensitized nanocrystalline TiO 2 solar cell is a new kind of photoelectron chemical solar cell. Because of its simple fabrication procedure, low cost, better stability and clean energy, the preparation of nanocrystalline TiO 2 has attracted an increasing interest of the world researchers. In this paper, TiO 2 film was obtained by spreading TiO 2 sol on the conductive glass substrate. To improve the performance of the photoelectrode, TiO 2 powder (P25) had been doped into the TiO 2 sol. Moreover, these films were sensitized by cis-dithiocyanato bis(4,4′-biscarboxy-2,2′-bipyridine) ruthenium in the anhydrous ethanol. XRD, XPS and AFM were used to characterize the microstructure, element composition and micrograph of the films. The results show that the crystal type of TiO 2 is a mixture of anatase and rutile TiO 2 , as well as the fact that photoelectricity property of the TiO 2 thin films is improved greatly by doping P25.

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