Interaction and transformation of metastable defects in intercalation materials

Non-equilibrium defects often dictate macroscopic functional properties of materials. In intercalation hosts, widely used in rechargeable batteries, high-dimensional defects largely define reversibility and kinetics. However, transient defects briefly appearing during ionic transport have been challenging to capture, limiting the understanding of their life cycle and impact. Here, we overcome this challenge and track operando the interaction and impact of metastable defects within NaxNi1-xMnyO2 intercalation hosts in a charging sodium-ion battery. Three-dimensional coherent X-ray imaging reveals transformation and self-healing of a metastable domain boundary, glissile dislocation loop, and stacking fault. A local strain gradient suggests a quantifiable difference in ion diffusion, coincident with the macroscopic change in diffusion coefficient. Analysis of the unexpected defect anisotropy highlights the importance of mesostructure, suggesting a possible control approach and disputing the rigidity of the framework layers. The shared nature of oxygen framework layers makes our results applicable to a wide range of intercalation materials.

Surface Behavior and Lattice Relaxation of SiGe/Si Strained Epitaxial Heterostructures

ABSTRACTThe correlation between the surface morphology and the lattice relaxation in strained SiGe/Si heteroepitaxy has been studied. It is found that the surface crosshateched pattern develops as the strained epilayer thickness increases. The effect of thermal annealing and boron dopant level has also been studied. The result suggests that the crosshatched morphology on the surface is constituted by surface slip steps of glissile dislocation motion in the strained epitaxial growth processing.