Determining atomistic structures of grain boundaries (GBs) is essential to understand structure–property interplay in oxides. Here, different GB superstructures in CuO nanosheets, including (111) and (114) twinning boundaries (TBs) and (002)/(223) GB, are investigated. Unlike the lower-energy stoichiometric (111) TB, both experimental and first-principles investigations reveal a severe segregation of Cu and O vacancies and a nonstoichiometric property at (114) TB, which may facilitate ionic transportation and provide space for elemental segregation. More importantly, the calculated electronic structures have shown the increased conductivity as well as the unanticipated magnetism in both (114) TB and (002)/(223) GB. These findings could contribute to the race towards the property-directing structural design by GB engineering.

Atomic-scale oxidation dynamics of Cu₂O nanocrystallines (NCs) are directly observed by in situ high-resolution transmission electron microscopy. A two-stage oxidation process is observed: (1) The initial oxidation stage is dominated by the dislocation-mediated oxidation behavior of Cu₂O NCs via solid-solid transformations, leading to the formation of a new intermediate CuO_x phase. The possible crystal structure of the CuO_x phase is discussed. (2) Subsequently, CuO_x is transformed into CuO by layer-by-layer oxidation. These results will help in understanding the oxidation mechanisms of copper oxides and pave the way for improving their structural diversity and exploiting their potential industrial applications.

The mechanical behavior of CuO nanowires (NWs) was investigated by in situ transmission electron microscopy. During compression, the NWs exhibited high bending capabilities associated with high mechanical stress. Interestingly, anelasticity was consistently observed after stress release. Further investigations indicate that the anelasticity is intrinsic to the CuO NWs, although electronbeam irradiation was proved capable of accelerating the shape recovery. A mechanism based on the cooperative motion of twin-associated atoms is proposed to account for this phenomenon. The results provide insight into the mechanical properties of CuO NWs, which are promising materials for nanoscale damping systems.