Dislocation toughening in single‐crystal KNbO₃

Abstract

The growing research interest in dislocation‐tuned functionality in ceramics is evident, with the most recent proofs‐of‐concept for enhanced ferroelectric properties, electrical conductivity, and superconductivity via dislocations. In this work, we focus on dislocation‐tuned mechanical properties and demonstrate that, by engineering high dislocation densities (up to 1014 m−2) into KNbO3 at room temperature, the fracture toughness can be improved by a factor of 2.8. The microstructures, including dislocations and domain walls, are examined by optical microscopy, electron channeling contrast imaging, piezo‐response force microscopy, and transmission electron microscopy methods to shed light on the toughening mechanisms. In addition, high‐temperature (above the Curie temperature of KNbO3) indentation tests were performed to exclude the influence of ferroelastic toughening, such that the origin of the toughening effect is pinpointed to be dislocations.

Mechanical tailoring of dislocations in ceramics at room temperature: A perspective

“…With the indentation crack length (ICL) method, we evaluated the fracture toughness and hardness, both are increased by ∼20%. A more significant increase of the dislocation-based fracture toughness by a factor of ∼3 using the ICL method is demonstrated on single-crystal KNbO 3 with a density up to ∼10 14 /m 2 (Figures 3A and B), 25 in line with the experimental protocol by Salem et al 24 Analogous to the functional properties, the mechanical properties are also found to be dependent on the dislocation density. Take the example of KNbO 3 , the higher fracture toughness is correlated to higher dislocation density (Figure 3C).…”

“…This opens an exciting new field for dislocation‐tuned functionality with proofs‐of‐concept established for photoconductivity, 13 electrical conductivity, 16–18 superconductivity, 19 and large‐signal piezoelectric coefficient ( d 33 *) 20 . From the mechanical point of view, once engineered into ceramics, dislocations can improve plasticity and increase fracture toughness (resistance to crack propagation) 21–25 . Both aspects will be elaborated on in the following section.…”

“…The urgent need for dislocation‐rich ceramic samples for testing versatile functionality and mechanical properties was the original driving force for the current author and his team to investigate mechanics‐based dislocation engineering in ceramics, with a particular focus on room‐temperature plastic deformation of ceramics for the sake of simple, fast, and energy‐efficient dislocation engineering. Targeting this objective, we have developed different experimental protocols and made promising progress 15,22,25,35–45 . In what follows, the author will first present an overview of dislocation‐tuned functional and mechanical properties in ceramics, demonstrating concrete examples to showcase the potential held by dislocations.…”

“…20 From the mechanical point of view, once engineered into ceramics, dislocations can improve plasticity and increase fracture toughness (resistance to crack propagation). [21][22][23][24][25] Both aspects will be elaborated on in the following section.…”

“…Targeting this objective, we have developed different experimental protocols and made promising progress. 15,22,25,[35][36][37][38][39][40][41][42][43][44][45] In what follows, the author will first present an overview of dislocation-tuned functional and mechanical properties in ceramics, demonstrating concrete examples to showcase the potential held by dislocations. Various approaches and methods for engineering dislocations into ceramics will be demonstrated, with a focus on a variety of boundary conditions and their impact on plasticity.…”