Electronic and structural properties of copper monoxide (CuO) sintered as a
common ceramic and nanoceramic are studied by positron annihilation
spectroscopy. A CuO nanoceramic with crystallite size ranging from 15 to 90 nm
was prepared from a common one by shock-wave loading. It is found
that the momentum distribution of valence electrons in CuO is shifted,
as compared with metallic copper, towards higher momentum values.
This result is related to the effect of the Cu 3d–O 2p hybridization in
the Cu–O ionic covalent bond formation. It is found that open volumes,
identified mainly as small agglomerates of oxygen vacancies, appear at the
nanoceramic crystallite interfaces. The degree of the Cu–O bond covalency
decreases locally at the crystallite interfaces because of an oxygen deficit. The
nanocrystalline state in CuO is shown to be thermally stable up to 700 K.
The kinetics of the isotope exchange between gaseous oxygen enriched with the 18O
isotope and two LaMnO3+δ oxide samples – a nanopowder and a bulk nanocrystal – has been
studied. The 18O isotope concentration has been measured by the acceleration nuclear microanalysis
method. The coefficients of the volume and the nanograin boundary self-diffusion of oxygen have
been evaluated at 500 °C. They are equal to 3.5·10
−20 and 1.5·10
−13 cm2/s, respectively.
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