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M. Niedermaier, C. Taniteerawong, T. Schwab, G. Zickler, J. Bernardi, O. Diwald:
"Impurity Segregation and Nanoparticle Reorganization of Indium Doped MgO Cubes";
ChemNanoMat, 5 (2019), 634 - 641.

Metal oxide nanocomposites are non-equilibrium
solids and promising precursors for functional materials.
Annealing of such materials can provide control over
impurity segregation and, depending on the level of
consolidation, represents a versatile approach to engineer
free surfaces, particle-particle interfaces and grain boundaries.
Starting with indium-magnesium-oxide nanoparticle
powders obtained via injection of an indium organic
precursor into the magnesium combustion flame and subsequent
particle quenching in argon, we investigated the
stability of the trivalent In3+ ions in the host lattice of MgO
nanoparticles by determining grain growth, morphology
evolution and impurity segregation. The latter process is
initiated by vacuum annealing at 873 K and can be tracked at
1173 K on a time scale of minutes. In the first instance the
surface segregated indium wets the nanoparticle interfaces.
After prolonged annealing indium evaporates and leaves the
powder via the gas phase. Resulting MgO nanocubes are
devoid of residual indium, regain their high morphological
definition and show spectroscopic fingerprints (UV Diffuse
Reflectance and Photoluminescence emission) that are characteristic
of electronically unperturbed MgO cube corner and
edge features. The results of this combined XRD, TEM, and
spectroscopy study reveal the parameter window within
which control over indium segregation is used to introduce a
semiconducting metal oxide component into the intergranular
region between insulating MgO nanograins.

http://dx.doi.org/10.1002/cnma.201900077