Particle attachment
and neck formation inside TiO2nanoparticle
networks determine materials performance in sensing, photo-electrochemistry,
and catalysis. Nanoparticle necks can feature point defects with potential
impact on the separation and recombination of photogenerated charges.
Here, we investigated with electron paramagnetic resonance a point
defect that traps electrons and predominantly forms in aggregated
TiO2nanoparticle systems. The associated paramagnetic
center resonates in thegfactor range betweeng= 2.0018 and 2.0028. Structure characterization and electron
paramagnetic resonance data suggest that during materials processing,
the paramagnetic electron center accumulates in the region of nanoparticle
necks, where O2adsorption and condensation can occur at
cryogenic temperatures. Complementary density functional theory calculations
reveal that residual carbon atoms, which potentially originate from
synthesis, can substitute oxygen ions in the anionic sublattice, where
they trap one or two electrons that mainly localize at the carbon.
Their emergence upon particle neck formation is explained by the synthesis-
and/or processing-induced particle attachment and aggregation facilitating
carbon atom incorporation into the lattice. This study represents
a substantial advance in linking dopants, point defects, and their
spectroscopic fingerprints to microstructural features of oxide nanomaterials.