On the spinel precipitation in Al-doped Ni{sub 1{minus}x}O

Journal Article · Thu Oct 01 04:00:00 EDT 1998 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.1998.7820· OSTI ID:305390

Wang, S R; Shen, P ^[1]

---

1. National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

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.

• OSTI ID: 305390
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 140; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CRYSTAL STRUCTURE
DISLOCATIONS
ELECTRON MICROSCOPY
EXPERIMENTAL DATA
NICKEL OXIDES
PRECIPITATION
SPINELS
STOICHIOMETRY
X-RAY DIFFRACTION