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.

High Entropy Approach to Engineer Strongly Correlated Functionalities in Manganites

“…Nevertheless, a recent dedicated TEM study has shown an enhanced degree of dislocation densities in pyrochlore‐HEO systems. [ 35 ] Hence, probing of unique and possibly enhanced lattice imperfections might be an interesting research avenue for HEOs in general. In addition, the defects observed here can also have a decisive influence on the properties, for instance, the missing plane (MnO) and the stacking fault‐like feature are likely to impact the MnOMn bonding characteristics that govern exchange interactions in manganites.…”

Medium-entropy ceramic aerogels for robust thermal sealing

“…Materials with increased conguration entropy have attracted broad interest due to their large enhancement in mechanical and thermal properties. 27,28,33,38,39 To investigate the increased-entropy effect in ceramics, we conducted molecular dynamics (MD) simulations with enhanced sampling methods [40][41][42] and machine learning potentials 43 in the unary, binary, ternary, and quaternary material systems (Fig. 1a, and Fig.…”

Mechanical property enhancements and amorphous thermal transports of ordered weberite-type RE3Nb/TaO7high-entropy oxides

“…High-entropy oxides (HEOs) are oxide solid solutions with one or more lattice sites occupied by equivalent/near-equivalent atoms of different elements [15]. Normally, the number (N) of elements in one or more lattice sites is greater than four in HEOs, [15,16], RE 3 NbO 7 [3,17], RE 2 Si 2 O 7 [18], and others [1922]. The properties of the aforementioned oxides have been successfully tailored and optimized, and thus the study of HEOs advances the development and application of various materials.…”

“…However, weberite-type RE 3 Nb/TaO 7 ceramics had inadequate mechanical properties, e.g., La 3 NbO 7 had hardness, toughness, and Young's modulus of approximately 4.5 GPa, 0.5 MPa•m 1/2 , and 100 GPa, respectively [23]. 7 yttria-stabilized zirconia (7YSZ), La 2 Zr 2 O 7 , and Yb 3 NbO 7 had high hardness (H = 913 GPa) and Young's modulus (E = 200250 GPa), and 7YSZ were widely used as protective coating materials due to their excellent fracture toughness (K IC = 3.5 MPa•m 1/2 ) [2,5,15,16,19]. The fluorite RE 3 Nb/TaO 7 HEOs have been studied to optimize their properties.…”

“…Therefore, it is necessary to improve properties of weberite-type RE 3 Nb/TaO 7 ceramics. References [3,15,17] have shown that grain refinement and solid solution strengthening enhance the hardness and modulus of high-entropy materials. Furthermore, increases in densities of dislocations and grain boundaries of HEOs improve the toughness.…”