Ali Gholinia

Large time-resolved in-situ electron backscatter diffraction (EBSD) datasets can now be acquired with high temporal resolution, but extracting quantitative grain-scale information remains challenging. Here, we present Track-Def, an automated post-acquisition workflow that converts repeated deformation EBSD maps into grain- and time-resolved statistics. The method was applied to an in-situ tensile EBSD dataset of Inconel 690 comprising 81 maps. After registration to a common reference frame, Track-Def tracked 1155 grains through the full loading sequence, corresponding to 93,555 grain observations, and extracted crystallographic, morphological and deformation descriptors. Geometrically necessary dislocation (GND) density was used as the principal deformation metric. Although the map-averaged GND density increased approximately linearly during plastic deformation, individual grains showed substantial differences in GND accumulation and intragranular heterogeneity. Analysis of individual grains, local clusters and texture-defined subsets showed that GND evolution depends on both crystallographic orientation and the local microstructural environment. Based on the tracked grain responses, Track-Def further distinguished stable and divergent grain subsets: divergent grains tended to be smaller and more frequently associated with triple junctions and complex grain-boundary configurations, whereas stable grains were generally larger and located in less complex local neighbourhoods. Track-Def therefore provides a practical framework for extracting statistically meaningful grain-resolved deformation information from large time-resolved EBSD datasets.

The CB (Bencubbin-like) chondrites are a metal-rich group of carbonaceous chondrites that probably formed in an impact-melt vapour plume resulting from a collision between two planetesimals. Many samples, for example the CBa-type meteorite Gujba, show evidence of secondary impact processes that occurred after formation, such as silicate-dominated impact melt veins. We investigated the texture, crystallographic microstructure and chemical composition of Fe,Ni metal particles in Gujba to distinguish primary features from those caused by secondary impact melting. We developed a qualitative classification relating the morphology of primary metal particles in Gujba to the extent that they were deformed by secondary impact melt. Electron backscatter diffraction analyses showed that less deformed Fe,Ni metal particles preserve a prior crystallographic structure, partially overprinted by recrystallization textures. Fe,Ni metal inside melt veins has been melted and recrystallized. Unmelted metal particles retain similar compositions to each other, but metal entrained in impact melt, and melted Fe,Ni metal differ slightly. Conditions on the CB parent body after secondary impact resulted in no significant equilibration between particles with primary compositions, probably as the effects of impact heating were relatively rapid. Metal–melt particles in larger systems from other planetary bodies may show more evidence of modification during impact melting.

When deformed by dislocation creep the dominant slip (Burgers) vectors of olivine dislocations are parallel to [100] or [001]. Dislocations with an [010] Burgers vector component (b dislocations) have been recorded rarely. Here we show an experimentally deformed olivine sample has a substantial population (17%) of b dislocations. Electron Backscatter Diffraction maps of crystal orientations provided information on dislocations from the orientation gradients. Maps show the b dislocations form subgrain walls like those formed by other dislocation types and are interpreted to form similarly by glide and climb, so b dislocations are mobile. To confirm our approach, we used Electron Backscatter Diffraction maps to select an area for Transmission Electron Microscopy imaging, down to an atomic scale image of a b dislocation. Our sample was deformed within range of subduction zone conditions; our approach can be used to investigate the scale and conditions of b slip in the mantle more widely.

Nanoscale crystals are becoming increasingly recognised in the products of volcanic eruptions, spanning a range of magma compositions. The crystallisation of nanolites impacts magma rheology, ascent dynamics, and eruptive style. Their impact can be enhanced due to their capacity to aggregate and develop neighbouring chemically differentiated boundary layers. However, their 3D interaction, spatial distribution, and morphology is not currently understood. Here we present a cutting-edge, 3D nanometre-scale visualisation and quantification of nanolites in scoriae of the Las Sierras-Masaya basaltic Plinian eruptions, acquired using X-ray ptychography. We find that Ti-magnetite nanolites aggregate, forming elongate, irregular structures in 3D. Their crystallisation extracts Fe and Ti from the melt, resulting in differentiated boundary layers with higher viscosity. Syn-eruptive crystallisation of nanolites and their interaction is estimated to have increased magma viscosity by 2–3 orders of magnitude, therefore, they likely had a strong control on magma rheology, increasing the potential of magma fragmentation.

The present study reports on the structural changes and related photovoltaic properties resulting from the addition of Ag in Cu(In,Ga)Se₂ (CIGS)-based thin-film solar cells analysed using two-dimensional (2D) and three-dimensional (3D) analytical and modelling techniques. The microstructures of CIGS and Ag-containing CIGS (ACIGS) layers were characterized by means of 2D and 3D electron backscatter diffraction (EBSD). Ag addition significantly increased grain sizes, which is differently observed in the 2D and 3D EBSD analyses due to the different methodology. Moreover, opto-electronic 3D device simulations, which incorporate real 3D structural data obtained from 3D EBSD, confirmed that 2D models tend to underestimate the impact of grain boundaries on the device performance. Device simulations showed that the increased grain size and thus, the decreased grain-boundary density, resulting from Ag addition had a positive effect on the open-circuit voltage (V _OC) of the solar cell. The V _OC improvement was more pronounced in ACIGS layers of high minority-carrier lifetimes. These findings highlight the necessity of combining 3D EBSD analysis with 3D device simulations to optimize the relationship between microstructural characteristics and photovoltaic performance in solar cells to understand opto-electronic properties more quantitatively.

Polycrystalline ferroelectrics constitute the basis of many advanced technologies, including sensors and actuators. Their intricate domain patterns, and switching, drive the macroscopic electrical and mechanical properties of the material, where the domain switching behaviour is largely influenced by the grain-grain interaction of the domain walls. Domain wall continuity across grain boundaries is speculated to affect the domain wall – grain boundary interaction, although the true impact of this phenomenon on the ferroelectric properties, and the conditions under which continuity occurs, are not yet well understood. Whilst there are some theoretical reports, the link to experimental evidence is limited, greatly hindering the applicability and fundamental understanding of current polycrystalline based devices. In this work, we close this gap by studying several grain junctions in free-standing BaTiO₃ thin films using microscopy techniques and rationalising the domain configurations with reference to martensite theory. A pleasing agreement of minimal strain and polarisation mismatch < 0.3 for a pair of domain variants were found in cases where domain wall continuity across grain boundaries was observed. Following this experimental validation, the mismatches for various combinations of Euler angles in bi-grain junctions were theoretically explored, offering valuable insights into specific cases where domain continuity can be expected. These results offer an advancement in the understanding of grain-grain-domain interactions and provides a template for the prediction and control of domain wall continuity in ceramic ferroelectrics, appealing to those working in polycrystal design and domain engineering.