Annual Report 2012 - Latvijas Universitātes Cietvielu fizikas institūts

Fig.1. Left panel: Schematic view of the nearest-neighbor relaxation around nickel vacancy in
the bulk of nickel oxide according to our molecular dynamics simulations. Note that oxygen
atoms move outwards, but nickel atoms move inwards to the nickel vacancy. Right panel:
Comparison of the experimental (solid lines) and configuration-averaged (dashed lines) Ni K-
edge EXAFS spectra χ(k)k 2 for nano-NiO and tf-NiO.
Within the MD-EXAFS method, the force-field potential models have been developed
for nanosized NiO using as a criterion the agreement between the experimental and
theoretical EXAFS spectra. The best solutions have been obtained for the 3D cubicshaped
nanoparticle models with nonzero Ni vacancy concentration C vac : C vac ≈ 0.4–
1.2% for NiO nanoparticles having the cube size of L ≈ 3.6–4.2 nm and C vac ≈ 1.6–2.0%
for NiO thin film composed of cubic nanograins with a size of L ≈ 1.3–2.1 nm. Thus our
results show that the Ni vacancies in nanosized NiO play important role in its atomic
structure relaxation along with the size reduction effect.
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