Plastic Deformation at the Nanoscale Bin Chen,1,2, * Wenge Yang,1 Jialin Lei,3 Shizhong Yang,3 Yuanjie Huang,1 HansRudolf Wenk,4 Ho-kwang Mao1,5 1Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China. *[email protected] 2Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA. 3LONI Institute, Southern University, Baton Rouge, LA 70813, USA 4Earth and Planetary Science, University of California, Berkeley, CA 94720, USA 5Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA The size of nanocrystals provides a limitation on dislocation activity and associated stress-induced deformation. Dislocation-mediated plastic deformation is expected to become inactive below a critical particle size, which has been proposed to be between 10 and 30 nm based on computer simulations and TEM analysis. However, our deformation experiments on polycrystalline nickel and magnesium aluminate suggest that dislocation activity is still operative in sub-10 nm crystals. Texturing and associated dislocation activities are observed for the first time in nanocrystals of a few nanometer sizes. Especially, through in situ texturing and TEM observations of stressed bulk- and nano-sized spinel ceramics, we find that dislocation activities become operative in nanoceramics. This new finding is at odds with the conventional theory that dislocation mechanisms are suppressed in ceramics.