Experimental and theoretical study of the Ni−(m-ZrO2) interaction

The present study examines the interaction between nickel and monoclinic zirconia (mZrO2). Nickel ions are adsorbed on ZrO2 and reduced by radiolysis. After irradiation and H2 treatment at 250 °C, XRD patterns reveal the presence of ZrO2 and interfacial phase Ni7Zr2. To estimate the shortest Ni−Zr distance, first principle density functional (DFT) calculations are used to study the Ni − mZrO2 interaction. First, the possibility of inserting atomic nickel in the bulk of ZrO2 is examined. Second, the effects of both insertion and adsorption on the stable surfaces of ZrO2, such as ( 1 ¯ 11) and ( 1 ¯ 01), 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 ( 1 ¯ 01), than through the surface ( 1 ¯ 11). Theoretical calculations show that adsorption and insertion on/in the surface processes may evolve with the formation of Ni–Zr–O complexes.