Nickel oxide-zirconium oxide: Ni2+ incorporation and its influence on the phase transition and sintering of zirconia

Nickel-containing ZrO2 samples (Ni up to 16.85%), prepared by contacting hydrous zirconium oxide (HZ) with an Ni2+ solution to a given pH were studied by various techniques (XRD, DTA, TG, XPS) to investigate the incorporation of Ni2+ in the ZrO2 structure in relation to the degree of dispersion of the transition-metal ions. Both dried (383 K) 'as prepared' and thermally treated (773 K, air) samples were investigated. The as-prepared samples were a mixture of amorphous particles of HZ and basic Ni nitrate crystallites, some very small in size. Heating at 773 K caused crystallisation of the HZ and transformation of the Ni compound into NiO. Concomitantly the Ni in the dispersed state entered the solid solution in the ZrO2 structure. The incorporation took place substitutionally in sites with trigonally distorted eightfold cubic symmetry. The presence of Ni favoured the formation of metastable tetragonal ZrO2 and affected the sintering process. The stability of the incorporated Ni2+ against reduction by hydrogen was also investigated. 28 refs.