Mechanical properties of ceria nanorods and nanochains; the effect of dislocations, grain-boundaries and oriented attachment

Abstract

We predict that the presence of extended defects can reduce the mechanical strength of a ceria nanorod by 70%. Conversely, the pristine material can deform near its theoretical strength limit. Specifically, atomistic models of ceria nanorods have been generated with full microstructure, including: growth direction, morphology, surface roughening (steps, edges, corners), point defects, dislocations and grain-boundaries. The models were then used to calculate the mechanical strength as a function of microstructure. Our simulations reveal that the compressive yield strengths of ceria nanorods, ca. 10 nm in diameter and without extended defects, are 46 and 36 GPa for rods oriented along [211] and [110] respectively, which represents almost 10% of the bulk elastic modulus and are associated with yield strains of about 0.09. Tensile yield strengths were calculated to be about 50% lower with associated yield strains of about 0.06. For both nanorods, plastic deformation was found to proceed via slip in the {001} plane with direction <110>--a primary slip system for crystals with the fluorite structure. Dislocation evolution for the nanorod oriented along [110] was nucleated via a cerium vacancy present at the surface. A nanorod oriented along [321] and comprising twin-grain boundaries with {111} interfacial planes was calculated to have a yield strength of about 10 GPa (compression and tension) with the grain boundary providing the vehicle for plastic deformation, which slipped in the plane of the grain boundary, with an associated <110> slip direction. We also predict, using a combination of atomistic simulation and DFT, that rutile-structured ceria is feasible when the crystal is placed under tension. The mechanical properties of nanochains, comprising individual ceria nanoparticles with oriented attachment and generated using simulated self-assembly, were found to be similar to those of the nanorod with grain-boundary. Images of the atom positions during tension and compression are shown, together with animations, revealing the mechanisms underpinning plastic deformation. For the nanochain, our simulations help further our understanding of how a crystallising ice front can be used to 'sculpt' ceria nanoparticles into nanorods via oriented attachment.

Communication: Different behavior of Young's modulus and fracture strength of CeO2: Density functional theory calculations

“…2(c) and 2(d)). Thus, a phase transition from a fluorite CeO 2 crystal structure is observed, which is in good agreement with the classical molecular dynamics simulation reported by Sayle et al 45 However, there are large differences between the calculated and experimental fracture strengths. A fracture strength of 22.7 GPa is obtained from the DFT calculation, whereas the experimental value is 0.250 GPa.…”

Designed Synthesis of CeO2 Nanorods and Nanowires for Studying Toxicological Effects of High Aspect Ratio Nanomaterials

“…Figure 4a shows the clear lattice fringes of {111} and {200} with interplanar spacings of 0.31 nm and 0.28 nm, indicating the cubic structure of CeO 2 nanorods with [211] growth direction. Although there is only one study reporting the synthesis of ceria nanorods with the same growth direction, 49 the feasibility of producing CeO 2 nanorods oriented along [211] was recently confirmed by Sayle et al 50 using atomistic simulation. By conducting detailed morphological analysis for nanorods formed at the early stage, Du et al 49 also successfully demonstrated that CeO 2 nanorods with the [211] orientation were grown by the so-called “oriented attachment” mechanism, in which adjacent nanoparticles are self-assembled by sharing a common crystallographic orientation followed by joining these particles at a planar interface, eventually leading to the development of single crystalline anisotropic structure.…”

Tuning the Properties of Nanoceria by Applying Force: Stress-Induced Ostwald Ripening

“…For example, a Σ3 grain boundary evolved within the 6 nm polyhedral nanoparticles, whereas a Σ11 grain boundary evolved in the 8 nm particle Previously, nanorods with Σ3 grain boundaries were calculated to have a compressive yield strength of 10 GPa. 38 Here, we find that 6 nm NP comprising Σ3 grain boundaries have an identical (10 GPa) compressive yield strength, which suggest that the shape is less important than the microstructure. Indeed, the 8 nm NP, which includes a Σ11 grain boundary, has a compressive strength of only 6 GPa.…”