AB INITIO STUDY OF FORMATION AND DIFFUSION OF OXYGEN-VACANCY COMPLEXES ON THE (111) NICKEL SURFACE. Cherbal Nadjia1, Megchiche El hocine1, Amarouche Mohand1 et C.Mijoule2 1Laboratoire de Physique et Chimie Quantique (LPCQ), Université Mouloud Mammeri(UMMTO) Tizi-Ouzou, Algerie. 2Ecole Nationale Supérieure des Ingénieurs en Arts Chimiques et Technologiques CIRIMAT-ENSIACET, Toulouse. UMMTO Introduction Many experimental and theoretical studies have been devoted recently to the subject of corrosion and oxidation of nickel-based alloys [1-3].in the present communication,we repot density functional theory (DFT) for generalized gradient approximation calculations has been used to study the formation processus of vacancies in surfaces(111) of nickel. We investigate systematically the site preference of atomic oxygen on perfect Ni(111) surface, we found that the fcc site is preferred over other adsorption sites, the calculated formation energy of monovacancy considering many geometrically configurations as first, second or third nearest neighbor site to the oxygen, suggest a strong stability of all these complexes. The pathways for oxygen diffusion on the perfect (111) surface have been investigated, two migration paths linking two fcc sites were considered: one in which the oxygen transits via a hcp site and one in which it transits via an atop site. We investigate the effect of monovacancy on the top layer of the (111) · Method 2. The formation processus of vacancyoxygen complexes on the (111) surface. Density Functional Theory Vienna Ab initio Simulation Package(VASP) Generalized Gradient approximation (GGA) FIG2:Monovacancy first nearst-neighbors (1NN), second nearest-neighbors 1. Oxygen adsorption at the perfect Ni(111) surface (2NN) and third nearest-neighbors (3NN)) of O on defect Ni(111). The red circle represent oxygen atom (O). FIG.1: Adsorption sites of atomic O on perfect Ni(111) surfaces. O atom is red circle. 1st Layer 2nd Layer 3rd Layer 1NN (d=1.85 A°) Fcc Hcp Top TAB.1: Adsorption sites, adsorption energy (Eads) and Ni-O bond distance for the O adsorption on perfect Ni(111) surface Adsorp. site Eads (eV) Fcc Hcp Bridge Top 5.47a , 5.50b , 5.56c 5.37a , 5.41b , 5.43C 4.93a , 4.96b, 5.28C 3.58a ,3.69b , 3.78C Ni-O bond distance (A°) 1.83a ,1.85C 1.84a ,1.85c 1.78a , 1.84c 1.76a, 1.84c Z12(℅) Z23(℅) -1.53 -1.92 -2.16 -0. 08 -0.18 0.45 0.54 -0.46 a This calculation b,c [ 4-5 ] 2NN (d=3,10 A°) 3NN (d= 3.97 A°) The energy gains compared to the reference system are of 3.80, 4.36 and 4.10 eV for the three configurations, respectively 3.Oxygen migration at the perfect Ni(111) surface 1,87 eV 0,53 eV It was shown that the fcc hollow site was the most stable site for atomic oxygen adsorption, wich is in accord with the previous DFT caculations. Conclusion DFT results reveal that the fcc hollow site is the most favorable for oxygen adsorption on perfect Ni(111) nickel surface. Our results of the formation processus of vacancies in surfaces(111) of nickel suggest a strong stability of all these complexes. ➢ we have at first studied migration of an oxygen ion on the perfect (111) surface. Our calculations showed that the stepwise diffusion ➢ pathway for fcc-hcp-fcc is more favorable than the direct jumping pathway. Oxygen atom is located on a Fcc hollow site on the perfect Ni(111) surface, we have investigated two different pathways,one in which the oxygen transits via a hcp site and one in which it transits via an atop site. The energetically favorable path is the one where the oxygen passes through the hcp site,the corresponding migration energy is 0.53 eV. References  S. Perusin, B.Viguier, D. Monceau, L.Ressier and E. Andrieu, Acta Mater, 52, 5375 (2004).  E.H. Megchiche, S. Pérusin, J.C. Barthelat and C. Mijoule, Phys. Rev., B 74,064111 (2006).  E.H. Megchiche, C. Mijoule and M. Amarouche, J.Phys.: condensed Matter 22, 485502 (2010).  M.Pozzo, G.Carlini, R.Rosei, Dario Alfe, J.Chem. Phys. 126 (2007) 164706.  N. K. Das, T. Shoji,Surf. Sci.258(2011) 442-447.
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