Functional and structural ceramics have become irreplaceable in countless high-tech applications. However, their inherent brittleness tremendously limits the application range and, despite extensive research efforts, particularly short cracks are hard to combat. While local plasticity carried by mobile dislocations allows desirable toughness in metals, high bond strength is widely believed to hinder dislocation-based toughening of ceramics. Here, we demonstrate the possibility to induce and engineer a dislocation microstructure in ceramics that improves the crack tip toughness even though such toughening does not occur naturally after conventional processing. With modern microscopy and simulation techniques, we reveal key ingredients for successful engineering of dislocation-based toughness at ambient temperature. For many ceramics a dislocation-based plastic zone is not impossible due to some intrinsic property (e.g. bond strength) but limited by an engineerable quantity, i.e. the dislocation density. The impact of dislocation density is demonstrated in a surface near region and suggested to be transferrable to bulk ceramics. Unexpected potential in improving mechanical performance of ceramics could be realized with novel synthesis strategies.

Most oxide ceramics are known to be brittle macroscopically at room temperature with little or no dislocation‐based plasticity prior to crack propagation. Here, we demonstrate the size‐dependent brittle to ductile transition in SrTiO ₃ at room temperature using nanoindentation pop‐in events visible as a sudden increase in displacement at nominally constant load. We identify that the indentation pop‐in event in SrTiO ₃ at room temperature, below a critical indenter tip radius, is dominated by dislocation‐mediated plasticity. When the tip radius increases to a critical size, concurrent dislocation activation and crack formation, with the latter being the dominating process, occur during the pop‐in event. Beyond the experimental examination and theoretical justification presented on SrTiO ₃ as a model system, further validation on α‐Al ₂ O ₃ , BaTiO ₃ , and TiO ₂ are briefly presented and discussed. A new indentation size effect, mainly for brittle ceramics, is suggested by the competition between the dislocation‐based plasticity and crack formation at small scale. Our finding complements the deformation mechanism in the nano‐/microscale deformation regime involving plasticity and cracking in ceramics at room temperature to pave the road for dislocation‐based mechanics and functionalities study in these materials.

The potential of dislocations (line defects) in ceramics may have been greatly underrated until most recently. Promising proofs‐of‐concept have been demonstrated for dislocation‐tuned functional and mechanical properties, revealing a new research front for dislocations in ceramics for a wide range of potential applications. However, it is commonly known that ceramics are hard (difficult to deform) and brittle (easy to fracture), particularly at room temperature. It remains a great challenge to mechanically tailor dislocations in ceramics. To address this pressing bottleneck, this article discusses the mechanics‐based dislocation engineering in ceramics by examining the three fundamental factors of dislocation nucleation, multiplication, and motion. Successful experimental approaches to tune dislocation density and plastic zone size on single‐crystal strontium titanate are demonstrated. The dislocation‐based competition between plastic deformation and crack formation is discussed. The aspects of coupling external fields to manipulate dislocations are highlighted, which may hold the key to modulating the charged dislocation cores in ceramics and opening new routes for mechanical tailoring of dislocations at room temperature. Some open questions and challenges for engineering dislocations in ceramics are discussed.