First-principles investigations of oxygen adsorption at TiNi surface and the TiO2/TiO-TiNi interface

Ab-intio study of the interaction of atomic and molecular oxygen with the TiNi(1 1 0) surface was performed using the projector augmented wave method with generalized gradient approximation for the exchange-correlation functional. The oxygen adsorption energies were calculated and the preferential adsorption sites of oxygen atom on the surface were determined. Our results confirmed the formation of a Ni-rich layer at the alloy-oxide interface. Atomic and electronic structure of both TiO/TiNi(1 1 0) and TiO2/TiNi(1 1 0) interfaces were analyzed. The formation energies (E-f) of point defects at the interfacial layers as well as in bulk TiNi, monoclinic TiO, and rutile TiO2 were estimated. It was shown that E-f of Ti-Ni swap defect has a lower energy than that for the Ni antisites at the TiO2(1 0 0)/TiNi(1 1 0) interface. In the case of TiO(1 0 0)/TiNi(1 1 0) interface, the formation energies of Ti-Ni swap and Ni-antisites defects are close to each other. Our results demonstrated that E-f of Ni-defect in TiO is twice less than that in TiO2. The increase in the formation energies of defects in TiO2 reveal the increase in diffusion barriers of Ni atoms in comparison with those in oxides with a lower oxygen content, which hampers Ni segregation. (C) 2013 Elsevier BY. All rights reserved.