纳米颗粒中的晶界演化

中文摘要 AI 辅助

晶界演化是使纳米颗粒发生结构重排并驱动其向低能构型转变的关键动力学过程；晶界还可增强催化性能，因此理解其演化的基本过程对纳米颗粒的晶界工程至关重要。与块体材料相比，纳米颗粒具有额外的转动和平动自由度，可通过形状弛豫容纳结构变化，且晶界终止于自由表面。然而，在这些约束较少的条件下，晶界（GB）演化的原子尺度机制相较于块体材料仍了解较少。本文采用原子模拟方法，聚焦于低能Σ3（共格孪晶界）和Σ11晶界——这是纳米颗粒结构演化过程中出现的持久致密晶界结构。研究人员在这些晶界及其结点的演化过程中，识别出两种基本原子位移：柱位移（C）和螺旋位移（S），二者通过不同原子路径发生，并以不同方式组合，引发晶界迁移、结构转变及结点演化。特别地，相同的初始和最终晶界构型可通过不同原子路径连接；柱位移既可完全发生，也可通过断开扭折实现；即使晶界特征发生变化（如Σ11向Σ3转变时），C和S仍可被识别。理解这些基本晶界过程有助于确定控制晶界演化的策略，从而实现纳米颗粒中晶界结构的工程调控。

英文摘要

Grain boundary evolution is a key dynamical process that enables structural rearrangements in nanoparticles and drives them towards low energy configurations. Grain boundaries can also enhance catalytic properties, making it important to understand the elementary processes underlying their evolution for grain boundary engineering in nanoparticles. Compared with bulk materials, nanoparticles have additional rotational and translational degrees of freedom, can accommodate structural changes through shape relaxation, and grain boundaries terminate at free surfaces. However, the atomic-scale mechanisms of GB evolution under these less constrained conditions remain comparatively less understood than in bulk materials. Here, using atomistic simulations, we focus on low energy $\Sigma3$ (coherent twin boundary) and $\Sigma11$ grain boundaries, which are among the persistent compact GB structures that emerge during nanoparticle structural evolution. We identify two fundamental atomic displacements, column shift (C) and screw shift (S), that recur during the evolution of these grain boundaries and their junctions. These displacements occur through different atomic pathways and combine in different ways to generate grain boundary migration, structural transformations, and junction evolution. In particular, the same initial and final grain boundary configurations can be connected through different atomic pathways, and a column shift can occur either as a full shift or through disconnection kinks. C and S remain identifiable even when the grain boundary character changes, for example during a $\Sigma11$ to $\Sigma3$ transformation. An understanding of these elementary GB processes can help identify strategies to control grain boundary evolution and thereby engineer GB structures in nanoparticles.

发表机构

• Sapienza Università di Roma（罗马大学）
• University of Stuttgart（斯图加特大学）
• Visvesvaraya National Institute of Technology（维斯瓦萨瓦亚国家理工学院）

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