Interdiffusion-induced phase changes of Co{sub 1{minus}x}O/zirconia composites

Journal Article · Thu Jul 01 00:00:00 EDT 1999 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.1998.8298· OSTI ID:679252

Lin, K T; Shen, P ^[1]

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

Co{sub 1{minus}x}O powders mixed with pure zirconia (ZrO{sub 2}) or yttria (Y{sub 2}O{sub 3}) partially stabilized zirconia (Y-PSZ) were sintered and annealed at 1300 C for 300 h, and the Co{sub 1{minus}x}O/Y-PSZ composite also at 1600 C for 1--100 h to investigate interdiffusion-induced phase changes. Analytical electron microscopic observations indicated the formation of (Zr, Y)-codoped Co{sub 3}O{sub 4} spinel from intra- and intergranular Co{sub 1{minus}x}O particles for all the fired composites. The spinel formation above the equilibrium temperature 900 C for pure Co{sub 1{minus}x}O/Co{sub 3}O{sub 4} pair can be rationalized by the substitution of Zr{sup 4+} (<2 mol%) and Y{sup 3+} (<1 mol%) for Co{sup 2+} to generate a considerable number of charge- and volume-compensating defects and paracrystalline array of defect clusters in the Co{sub 1{minus}x}O lattice. The (111) faulting of (Zr, Y)-codoped Co{sub 3}O{sub 4} implies the possible presence of Zinc blende-type defect clusters with cation vacancies assembled along oxygen close packed (111) plane of Co{sub 1{minus}x}O. About 6 mol% Co{sup 2+} dissolution of Y-PSZ was found to stabilize the cubic-phase of zirconia upon cooling to room temperature. A relatively larger flux of Co{sup 2+} from Co{sub 1{minus}x}O into Y-PSZ than the opposite flux of Zr{sup 4+} and Y{sup 3+} causes a net vacancy flux, hence the formation of Kirkendall pores around the Co{sub 1{minus}x}O particles.

• OSTI ID: 679252
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 145; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COBALT OXIDES
COMPOSITE MATERIALS
DIFFUSION
EXPERIMENTAL DATA
MICROSCOPY
PHASE STUDIES
TEMPERATURE RANGE 1000-4000 K
X-RAY DIFFRACTION
ZIRCONIUM OXIDES