Abstract:
The structural and physicochemical properties of metal/oxide interface remain the subject of
experimental and theoretical studies due to their important technological application in
microelectronics, laser optics, chemistry, high-pressure physics, medicine, etc.
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.
For the XRD spectra, of samples impregnated with Ni loads of 5% and 7.5% and calcined at
several temperatures, have showed the presence of ZrO2 and interfacial phases (NiZr2,
Ni0.99Zr0.01, NiO) beyond 550°C. While the XRD patterns, of samples impregnated with Ni
loads of 5% and reduced with hydrogen flow at 350°C, have showed only the presence of
intermetallic phases (NiZr2, Ni0.99Zr0.01) in addition to the ZrO2 support.
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 (111) and(101) , 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(101) , than through the surface(111) . Theoretical
calculations show that adsorption and insertion on/in the surface processes may evolve with
the formation of Ni–Zr–O complexes.
