On the Spinel Precipitation in Al-Doped Ni1−xO

✍ Scribed by S.R. Wang; P. Shen

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 874 KB
• Volume: 140
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7820

✦ Synopsis

The Ni 1-x O/NiAl 2 O 4 (69 : 1 molar ratio) composite fired at 1873 K for 1-80 h and then slowly cooled or water quenched in air was studied by X-ray diffraction and electron microscopy to clarify the stoichiometry, microstructures, and formation mechanism of spinel precipitates in Al-doped Ni 1-x O. Expulsion of Al 3؉ during slow cooling caused the formation of stoichiometric NiAl 2 O 4 precipitates which contained + +110, , domain boundaries of spinelloid nature and were of the same size regardless of the firing time at 1873 K. Instead of growing at NiAl 2 O 4 seeds, the spinel precipitate nucleated from dislocations (line vector parallel to 1 11002 2), hence with + +100, , rather than close-packed + +111, , as the habit plane. The + +100, , interface is coherent given that the lattice parameter for NiAl 2 O 4 is almost exactly twice that of Ni 1-x O. On the basis of diffusion data reported for Al-doped Ni 1-x O single crystals, we suggest that below 1473 K, moving of some Al 3؉ dopant from octahedral to interstitial tetrahedral sites caused the spinel nucleation to preferentially occur at dislocation cores with beneficial higher diffusivity and lower activation energy for defect clustering.