Role of Nanostructuring on the Properties of Oxide Materials: The Case of Zirconia Nanoparticles

In this review we discuss how the geometric structures, the stability, the reactivity, and the magnetic properties of zirconia nanoparticles (NPs) may differ substantially from those of bulk zirconia or of the (101) ZrO 2 surface. Based on extensive density functional calculations, we show that the formation energies of neutral oxygen vacancies are considerably smaller in zirconia NPs than those on the zirconia surface. The presence of low-coordinated sites on the NPs generates defective states in the band gap of the material that results in enhanced chemical activity towards adsorbed molecular or atomic species, which also affects the physical properties. In particular, the following cases have been considered comparing zirconia bulk and NPs: (1) the adsorption of a Au atom; (2) the adsorption of a H 2 molecule; (3) the reduction of zirconia via H 2 O desorption from a hydroxylated surface; (4) the appearance of high-spin, magnetic ground states in reduced zirconia NPs. This provides evidence that nanostructuring can turn zirconia, a non-reducible, non-magnetic material, into a reducible magnetic oxide