Surface Ni2+ ion diffusion into sol-gel tetragonal and monoclinic matrices was studied by means of Fourier transform infra-red spectroscopy, differential thermal analysis and X-ray photo-electron spectroscopy. It was found that the Ni2+ ions diffused continuously, at temperatures ranging from 400 to 600C, into both the tetragonal and monoclinic phases. They later formed a thermodynamically stable Ni2+/ZrO2 solid solution at high calcination temperatures. Higher Ni2+ surface contents in tetragonal ZrO2 were detected by X-ray photo-electron spectroscopy; thus indicating a larger specific surface area for a tetragonal gel matrix. In addition to the 2+ oxidation state, 3+ was also detected for Ni in ZrO2 systems. The atomic ratio, Ni2+/Ni3+, peaked at 700C in tetragonal material. However, in monoclinic material, the ratio remained constant throughout the experiments. The activation energy for the diffusion of Ni2+ ions in ZrO2 matrices was estimated to be 0.40eV.

H.C.Zeng, J.Lin, W.K.Teo, F.C.Loh, K.L.Tan: Journal of Non-Crystalline Solids, 1995, 181[1-2], 49-57