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Author Wang, S. R. ♦ Shen, P.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ CRYSTAL STRUCTURE ♦ NICKEL OXIDES ♦ ALUMINIUM OXIDES ♦ X-RAY DIFFRACTION ♦ ELECTRON MICROSCOPY ♦ STOICHIOMETRY ♦ PRECIPITATION ♦ SPINELS ♦ DISLOCATIONS ♦ EXPERIMENTAL DATA
Abstract The Ni{sub 1{minus}x}O/NiAl{sub 2}O{sub 4} (69:1 molar ratio) composite fired at 1,873 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{sub 1{minus}x}O. Expulsion of Al{sup 3+} during slow cooling caused the formation of stoichiometric NiAl{sub 2}O{sub 4} precipitates which contained {l_brace}110{r_brace} domain boundaries of spinelloid nature and were of the same size regardless of the firing time at 1,873 K. Instead of growing at NiAl{sub 2}O{sub 4} seeds, the spinel precipitate nucleated from dislocations (line vector parallel to {l_angle}100{r_angle}), hence with {l_brace}100{r_brace} rather than close-packed {l_brace}111{r_brace} as the habit plane. The {l_brace}100{r_brace} interface is coherent given that the lattice parameter for NiAl{sub 2}O{sub 4} is almost exactly twice that of Ni{sub 1{minus}x}O. On the basis of diffusion data reported for Al-doped Ni{sub 1{minus}x}O single crystals, the authors suggest that below 1,473 K, moving of some Al{sup 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.
ISSN 00224596
Educational Use Research
Learning Resource Type Article
Publisher Date 1998-10-01
Publisher Place United States
Journal Journal of Solid State Chemistry
Volume Number 140
Issue Number 1


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