Boudjennad E.,Laboratoire Microstructure et Defauts dans les Materiaux |
Boudjennad E.,University Pierre and Marie Curie |
Chafi Z.,Laboratoire Microstructure et Defauts dans les Materiaux |
Chafi Z.,University Pierre and Marie Curie |
And 4 more authors.
Surface Science | Year: 2012
The present study examines the interaction between nickel and monoclinic zirconia (mZrO 2). Nickel ions are adsorbed on ZrO 2 and reduced by radiolysis. After irradiation and H 2 treatment at 250°C, XRD patterns reveal the presence of ZrO 2 and interfacial phase Ni 7Zr 2. To estimate the shortest Ni-Zr distance, first principle density functional (DFT) calculations are used to study the Ni - mZrO 2 interaction. First, the possibility of inserting atomic nickel in the bulk of ZrO 2 is examined. Second, the effects of both insertion and adsorption on the stable surfaces of ZrO 2, such as (1̄11) and (1̄01), are studied. It is shown that an increase amount of inserted nickel, from one Ni for 4 Zr to an equivalent amount, enhances the insertion energy and makes insertion more exothermic. This phenomenon is accompanied by a lattice expansion (6-26%) and a reduction of symmetry. When the nickel is inserted in the bulk, the distance Ni-Zr is equal to 2.57 Å, which is in agreement with experimental value. Surface insertion and adsorption calculations show that nickel atoms can penetrate inside the oxide much more easily across the surface (1̄01), than through the surface (1̄11). Theoretical calculations show that adsorption and insertion on/in the surface processes may evolve with the formation of Ni-Zr-O complexes. © 2012 Elsevier B.V. All rights reserved.