Atomic scale defects play a key role in determining the behaviour of all crystalline materials, profoundly modifying mechanical, thermal and electrical properties. Many current technological applications make do with phenomenological descriptions of these effects; yet myriad intriguing questions about the fundamental link between defect structure and material function remain.
Transmission electron microscopy revolutionised the study of atomic scale defects by enabling their direct imaging. The novel coherent X-ray diffraction techniques developed in this project promise a similar advancement, making it possible to probe the strain fields that govern defect interactions in 3D with high spatial resolution (<10 nm). They will allow us to clarify the effect of impurities and retained gas on dislocation strain fields, shedding light on opportunities to engineer dislocation properties. The exceptional strain sensitivity of coherent diffraction will enable us to explore the fundamental mechanisms governing the behaviour of ion-implantation-induced point defects that are invisible to TEM. While we concentrate on dislocations and point defects, the new techniques will apply to all crystalline materials where defects are important. Our characterisation of defect structure will be combined with laser transient grating measurements of thermal transport changes due to specific defect populations. This unique multifaceted perspective of defect behaviour will transform our ability to devise modelling approaches linking defect structure to material function.
A deep, fundamental understanding of atomic scale defects and their effect on material function is an essential prerequisite for exploiting and engineering defects to enhance material properties for next generation power generation, energy storage and transport applications.
At the conclusion of this project, we were able to fully realise the goals formulated at the outset. The new X-ray techniques developed in this project enable unique insight into the nanoscale insitu structure of crystal defects. They have become universally accepted in the field and are now a cornerstone for upgrades under way at major synchrotron facilities worldwide. In irradiation-damaged materials we established the presence of a large, previously overlooked population of point defects too small to be observed by TEM. By combining experiments with atomistic simulations, we could establish the clear link between these defects and dramatic changes in material properties. These insights are of pivotal importance of the design of materials for intense irradiation environments in next generation fission and fusion power reactors.
