Structural Analysis of HR-TEM Images of Ni-doped Zirconia Nanoparticles

Zirconia has high thermal stability, low thermal conductivity, and high resistance to corrosion. Therefore, it is used as refractory materials, pigments, piezoelectric devices, ceramic capacitors, oxygen sensors, and as catalysts, among other uses Zirconia in pure form, exhibits three well-defined polymorphs. At room temperature, it has a monoclinic structure, at 1170C is tetragonal and after 2370C, the structure is cubic The m-ZrO2/t-ZrO2 transformation is thermodynamically reversible while the c-ZrO2 is only thermodynamically stable at temperatures above 2370 C [3]. However, the addition of certain aliovalent oxides can stabilize the t-ZrO and c-ZrO2 structures at room temperature. Between these aliovalent oxides, the NiO has been found to be a good candidate for the stabilization of both structures. On the other hand, the Ni-ZrO2 system is very important because can be used as catalyst in the partial oxidation of methane into higher hydrocarbons. Previous works have evidenced that Zr 4+ ions were found to substitute Ni 2+ ions in the NiO lattice forming a ZrO2-NiO solid solution This produces strong interaction between Zr and Ni atoms decreasing the NiO reducibility and modifying the nature of oxygen species adsorbed, which plays an important role in the catalytic performance. Therefore, gain insight about the crystalline structure of Ni-doped ZrO2 nanoparticles is important in order to improve the new synthesis routes with a better catalytic performance.