Formation of a one-dimensional dislocation loop array in wurtzite zinc oxide at ambient temperature

• First demonstration of ordered prismatic dislocation loop array in brittle ceramics • Stable PDL arrays experimentally observed in single-crystal ZnO at room temperature • Loops verified by 3D TEM and machine-learning-potential atomic simulations • Force-balance model proposed for pile-up of dislocation loop array in brittle solid Introducing highly ordered dislocation configurations into brittle solids remains a significant challenge because of their inherently limited dislocation mobility. A prototypical example is the prismatic dislocation loop (PDL) array, and whether it can form and remain stable in brittle solids, as it does in metals, remains an open question. In this work, we show the formation of a long, one-dimensional array of PDLs in wurtzite zinc oxide ceramics using nanoindentation, confirmed by transmission electron microscope observations of their three-dimensional configurations and atomistic simulation based on our state-of-the-art neural network potential. Each PDL consisted of alternating basal and prismatic-I edge dislocation segments with a Burgers vector b = 1/3[ 11 2 ¯ 0 ], forming a closed dislocation loop. Nearly identical PDLs were continuously punched into the sample by the indenter and piled up along the [ 11 2 ¯ 0 ] direction. As a result, a one-dimensional dislocation loop array formed, while the surrounding region remained dislocation-free. We demonstrate that the loop spacing can be predicted within a theoretical framework based on the force-balance condition of dislocation loops, in agreement with experimental observations. This research not only advances the understanding of dislocation-based plasticity but also provides a strategy for the controlled formation of highly ordered PDL arrays in brittle technologically critical materials.