Small-Size-Induced Plasticity and Dislocation Activities on Non-Charge-Balanced Slip System of Ionic MgO Pillars

We observed the small-size-induced hardening and plasticity of brittle ionic MgO as a result of abnormally triggered dislocation gliding on a non-charge-balanced slip system. The indentation tests of ⟨111⟩ MgO pillars revealed an increased hardness with decreasing pillar size, and the tips of the pillars that were ≤200 nm were plastically deformed. The in situ compression tests of ⟨111⟩ MgO nanopillars in transmission electron microscopy verified aligned dislocation-mediated plasticity on the {111}⟨110⟩ and {100}⟨110⟩ systems rather than the charge-balanced {110}⟨110⟩ slip system.