Dept. Engineering and Applied Science, Cranfield University, Defence Academy of the United Kingdom, Shrivenham, SN6 8LA, UK.
Nanoscale. 2011 Apr;3(4):1823-37. doi: 10.1039/c0nr00980f. Epub 2011 Mar 15.
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.
我们预测，扩展缺陷的存在会使氧化铈纳米棒的机械强度降低 70%。相反，原始材料可以在接近其理论强度极限的情况下变形。具体来说，已经生成了具有完整微观结构的氧化铈纳米棒的原子模型，包括：生长方向、形态、表面粗糙化（台阶、边缘、角）、点缺陷、位错和晶界。然后，使用这些模型来计算微观结构对机械强度的影响。我们的模拟表明，直径约为 10nm 且没有扩展缺陷的氧化铈纳米棒的压缩屈服强度分别为[211]和[110]取向的 46 和 36GPa，这代表了近 10%的体弹性模量，与约 0.09 的屈服应变相关。拉伸屈服强度计算值低约 50%，对应的屈服应变为约 0.06。对于两种纳米棒，塑性变形都被发现是通过沿<110>方向的{001}面的滑移进行的，这是萤石结构晶体的主要滑移系统。取向为[110]的纳米棒的位错演化是由表面存在的铈空位引发的。计算结果表明，取向为[321]并包含具有{111}界面的孪晶界的纳米棒在压缩和拉伸时的屈服强度约为 10GPa，晶界是塑性变形的载体，在晶界平面内滑移，具有相关的<110>滑移方向。我们还通过原子模拟和 DFT 的结合预测，当晶体受到拉伸时，金红石结构的氧化铈是可行的。通过模拟自组装生成的包含取向附生的单个氧化铈纳米颗粒的纳米链的力学性能与具有晶界的纳米棒相似。展示了拉伸和压缩过程中原子位置的图像和动画，揭示了塑性变形的机制。对于纳米链，我们的模拟有助于进一步理解如何通过结晶冰前沿将氧化铈纳米颗粒“雕刻”成纳米棒。
