Ultra-dense dislocations stabilized in high entropy oxide ceramics

Abstract

Dislocations are commonly present and important in metals but their effects have not been fully recognized in oxide ceramics. The large strain energy raised by the rigid ionic/covalent bonding in oxide ceramics leads to dislocations with low density (∼10⁶ mm⁻²), thermodynamic instability and spatial inhomogeneity. In this paper, we report ultrahigh density (∼10⁹ mm⁻²) of edge dislocations that are uniformly distributed in oxide ceramics with large compositional complexity. We demonstrate the dislocations are progressively and thermodynamically stabilized with increasing complexity of the composition, in which the entropy gain can compensate the strain energy of dislocations. We also find cracks are deflected and bridged with ∼70% enhancement of fracture toughness in the pyrochlore ceramics with multiple valence cations, due to the interaction with enlarged strain field around the immobile dislocations. This research provides a controllable approach to establish ultra-dense dislocations in oxide ceramics, which may open up another dimension to tune their properties.

Dislocation engineering is important for designing structural materials. Here the authors demonstrate that a high-entropy oxide ceramic with a high density of edge dislocations can be stabilized by increasing the compositional complexity, resulting in enhanced fracture toughness.