On the delayed incipient plastic deformation in a LiTaO₃ single crystal by nanoindentation

Relying on nanoindentation technology, the process of elastic-to-elastoplastic transition can be traced at the nanoscale via the sudden excursion in depth, namely the first pop-in event. In the current work, we investigated the delayed incipient plastic deformation at the holding stage in a LiTaO₃ single crystal under a 9.8 µm spherical tip. The critical loads for spontaneous incipient plasticity fall in a wide range on the X-112° (1¯ 1 0 2) and Y-42° (0 1 1¯ 2) planes. The delayed incipient plasticity partially occurs in those elastic holding tests. The effects of atomic orientation, holding load and loading rate on the occurrence probability and length scale of delayed incipient plasticity were revealed. The delaying mechanism of incipient plasticity was qualitatively discussed based on the evolution of the plastic unit beneath nanoindentation.