Spontaneous bending of the coalesced α-Cr₂O₃ nanocondensates: implications for multilayer coating systems

Nanosized α-Cr₂O₃ bicrystals with a special boundary of mixed planes via (hkil)-specific coalescence were formed by pulsed laser ablation on Cr in oxygen atmosphere. Transmission electron microscopy observations indicated that the bicrystals consist of rhombic (denoted as r) and platy (denoted as p) parts with well-developed \( \left( {10\bar{1}\bar{2}} \right)_{\text{r}} \)//(0001)_p interface and exact \( \left[ {{\bar{\text{2}}\text{2}}0\bar{1}} \right]_{\text{r}} //\left[ {{\bar{\text{1}}\text{1}}00} \right]_{\text{p}} \) alignment, where \( \left( {10\bar{1}\bar{2}} \right)_{\text{r}} \) belongs to a prevailed group nonequivalent to \( \left( {10\bar{1} 2} \right)_{\text{r}} \) due to the \( \bar{3} \)(inverse triad) operation. The nanoplate was significantly bent when anchored on the ledged \( \left( {10\bar{1} \bar{2} } \right)_{\text{r}} \) surface of the nanorhomb. The hoop stress by the combined factors of anchorage points, capillarity force, and lattice/thermal mismatch accounts for the bending of the nanoplate. Such understanding sheds light on the bending mechanism of more complicated multilayer coatings generally with residual stress via islands coalescence.