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Equilibration processes at NiO surfaces
Author(s) -
Nowotny J.,
Sloma M.,
Weppner W.
Publication year - 1988
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740120408
Subject(s) - non blocking i/o , single crystal , crystal (programming language) , oxygen , materials science , kinetics , analytical chemistry (journal) , work function , cubic zirconia , chemistry , layer (electronics) , crystallography , nanotechnology , metallurgy , physics , ceramic , biochemistry , organic chemistry , chromatography , quantum mechanics , computer science , programming language , catalysis
Work function (WF) measurement were performed to monitor defect processes at the surface of NiO single crystals during re‐equilibration at elevated temperatures using gas atmospheres of controlled oxygen activities. The WF data are reported for isothermic redox experments performed at 780°C within an oxygen activity ranging between 1.74 × 10 2 and 4.3 × 10 −4 Pa. Determination of the WF is based on the measurements of the contact potential differences by the Kelvin probe. Pt was applied as a reference level. Y‐stabilized zirconia was used for calibration of the reference electrode under experimental conditions. The WF data obtained for a NiO single crystal are evaluated in terms of point defect equilibrai in the nearsurface region. It is shown that the ideal defect model is applicable for a freshy cleaved NiO surface within about 20 h of treatment at 780°C. At longer times the near‐surface defece defect model becomes more complicated involving strong defect interactions. The complications are mainly produced by segregation of bulk extrinsci defects. The outer crystal layer of the studied NiO material becomes signficantly enriched with Ca which segregates to surfaces and presumably to grain boundaries. The impact of the experimental data of the kinetics of high temperature heterogeneous processes is discussed.