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Dion–Jacobson compounds have a layered perovskite structure, and a small number of them have been identified as being ferroelectric. Here, RbBiNb2O7 powders are made by conventional solid-state synthesis. The relatively large Rb ion produces an interlayer within the structure with a large spacing and weak bonding. This work shows for the first time that a polar layered perovskite can be exfoliated into 2D nanosheets using a facile and scalable method, namely liquid-phase sonication. With both 2D materials and ferroelectrics being of interest for photocatalysis, the photocatalytic performance of RbBiNb2O7 nanosheets is characterized by measuring its dye degradation rate under a solar simulator. It is demonstrated that the RbBiNb2O7 nanosheet material effectively decolourizes Rhodamine B under visible illumination even though it has a wide bandgap (3.45 eV), and that its photocatalytic activity is greatly enhanced (∼4 times faster) when decorated with photodeposited Ag nanoparticles. Reducing the nanosheet size also increases the photocatalytic performance. This work demonstrates that polar 2D Dion–Jacobson phase RbBiNb2O7 is a promising candidate for photocatalytic applications. Further improvements are possible by identifying compounds with a narrower bandgap as a broad compositional window is available in this family of compounds.

We report the synthesis of sustainable ordered mesoporous carbons (OMCs) produced from lignin, using the evaporation induced self-assembly (EISA) method. We demonstrated that it is possible to replace half of the phloroglucinol (a well-known carbon precursor currently not derived from bioprecursors) by hardwood organosolv lignin while obtaining a highly ordered pore structure. Notably, we also used glyoxal instead of formaldehyde as a crosslinker, which makes the synthesis route even “greener” with respect to the toxicity of the precursors and their renewable sourcing. Finally, we demonstrated that the resulting carbons make powerful electrodes in supercapacitors and we have made clear correlations between the porous structure and their electrochemical performance in symmetric supercapacitors in order to deliver tailored energy storage to meet various demands (i.e. amount of charge stored vs. power of delivery).

Controlling the assembly of molybdenum disulfide (MoS

Dielectric materials, with high tunability at microwave frequencies, are key components in the design of microwave communication systems. Dense Ba0.6Sr0.4TiO3 (BST) ceramics, with different grain sizes, were prepared in order to optimise the dielectric tunability via polar nano cluster effects. Dielectric permittivity and loss measurements were carried at both high and low frequencies and were supported by results from X-ray powder diffraction, scanning and transmission electron microscopies, Raman spectroscopy and piezoresponse force microscopy. The concentration of polar nano clusters, whose sizes are found to be in the range 20 to 50 nm, and the dielectric tunability increase with increasing grain size. A novel method for measurement of the microwave tunability in bulk dielectrics is presented. The highest tunability of 32% is achieved in ceramics with an average grain size of 10 um. The tunability of BST ceramics with applied DC field is demonstrated in a prototype small resonant antenna., 25pages, 6 figures

The Center for Predictive Integrated Structural Materials Science (PRISMS Center) is creating a unique framework for accelerated predictive materials science and rapid insertion of the latest scientific knowledge into next-generation ICME tools. There are three key elements of this framework. The first is a suite of high-performance, open-source integrated multi-scale computational tools for predicting microstructural evolution and mechanical behavior of structural metals. Specific modules include statistical mechanics, phase field, crystal plasticity simulation and real-space DFT codes. The second is the Materials Commons, a collaboration platform and information repository for the materials community. The third element of the PRISMS framework is a set of integrated scientific “Use Cases” in which these computational methods are linked with experiments to demonstrate the ability for improving our predictive understanding of magnesium alloys, in particular, the influence of microstructure on monotonic and cyclic mechanical behavior. This paper reviews progress toward these goals and future plans.

For Al alloys (e.g. Al-Si series) surface treatment like anodizing is a necessary step for applications in aggressive environments. Si-surface enrichment caused by processing can alter importantly the anodizing process. Model alloys with Si supersaturated in Al layer grown by PVD have been used to investigate the effect of the Si content on the anodizing process. Different Si concentrations of 0, 4, 7, 10 at.% are considered and compared. The morphology and in-depth microstructure of the oxides are derived for the different Si contents and anodizing potentials. Si was found to have a dramatic effect on the void and defect formation during barrier Al oxides growth even for Si concentrations as low as 4 at.%. Importantly, the anodizing oxide layer appears to be heterogeneous in the cross section, with Si accumulation close to the metal oxide interface while pure Al oxide is first formed as a barrier on the top surface.

Aging of Mg Nd alloys involves the formation of Guinier-Preston zones followed by β‴ precipitation that is associated with peak hardness. Using atom probe tomography and high-angle annular dark-field scanning transmission electron microscopy, the three-dimensional morphologies of the coherent Guinier-Preston zones and β‴ precipitates were quantified. The Guinier-Preston zones form equiaxed plates while the β‴ precipitates are elongated along the [0001]Mg direction thereby minimizing elastic strains. The β‴ precipitates exhibit additional faceting along the [0001]Mg direction and along the 1 1 01 Mg and 1 1 02 Mg directions when viewed along the 11 2 0 Mg zone axes, which can be affected by strain field interactions from nearby precipitates.

This study addresses the phase stability and atomic mobility of Ag-Cu40at.% nano-alloys confined by AlN in a nanomultilayered configuration during thermal treatment. To this end, nanomultilayers (NMLs) with a fixed Ag-Cu40at.% nanolayer thickness of 8 nm and a AlN barrier nanolayer with variable thickness of 4, 8, or 10 nm were deposited by magnetron sputtering on sapphire substrates and subsequently isothermally annealed for 5 or 20 min in air in the range of 200-500 °C. The microstructure of the as-deposited and heat-treated NMLs was analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. Annealing of the thicker AlN barrier layers at T > 300 °C leads to the formation of an interconnected network of line-shaped Cu(O) protrusions on the annealed NML surface. The well-defined outflow pattern of Cu(O) originates from the thermally induced surface cracking of the top AlN barriers with subsequent fast mass transport of Cu along the Cu/AlN interfaces toward the surface cracks. The thinnest (i.e., 4 nm thick) AlN barrier layers exhibit a relatively open grain boundary structure and act as nanoporous membranes upon heating, resulting in the formation of a dense and homogenous distribution of Cu(O) and Ag droplets on the NML surface. These findings demonstrate that the microstructure (i.e., layer thicknesses, interface coherency, and texture) of hybrid nanolaminates can be tuned to provide defined pathways for fast, directional transport of the confined metal to the surface at relatively low temperatures, which might open new routes for low-temperature bonding of micro- and nano-scaled systems.

Isothermal oxidation of (Hf-Ta-Zr-Nb)C high entropy carbide (HEC4) was performed using thermo-gravimetric analysis at 800−1100 °C in air. Polycrystalline oxide layers with multi-element oxides were observed, and their thickness increased with increasing oxidation temperature. Particular attention was paid to the microstructure and role of the interface. An amorphous and compact oxycarbide interlayer was observed between the oxide layer and the bulk carbide in oxidized HEC4, providing an effective diffusion barrier during oxidation. There was a through thickness distribution of the metals in the oxide layer, because of the different oxidation rates and outward diffusion of the cations.

In this article, after a brief introduction to the principles behind atom probe crystallography, we introduce methods for unambiguously determining the presence of crystal planes within atom probe datasets, as well as their characteristics: location; orientation and interplanar spacing. These methods, which we refer to as plane orientation extraction (POE) and local crystallography mapping (LCM) make use of real-space data and allow for systematic analyses. We present here application of POE and LCM to datasets of pure Al, industrial aluminium alloys and doped-silicon. Data was collected both in DC voltage mode and laser-assisted mode (in the latter of which extracting crystallographic information is known to be more difficult due to distortions). The nature of the atomic planes in both datasets was extracted and analysed.

Because atom probe tomography (APT) provides three-dimensional reconstructions of small volumes by resolving atomic chemical identities and positions, it is uniquely suited to analyze solute clustering phenomena in materials. A number of approaches have been developed to extract clustering information from the 3D reconstructed dataset, and numerous reports can be found applying these methods to a wide variety of materials questions. However, results from clustering analyses can differ significantly from one report to another, even when performed on similar microstructures, raising questions about the reliability of APT to quantitatively describe solute clustering. In addition, analysis details are often not provided, preventing independent confirmation of the results. With the number of APT research groups growing quickly, the APT community recognizes the need for educating new users about common methods and artefacts, and for developing analysis and data reporting protocols that address issues of reproducibility, errors, and variability. To this end, a round robin experiment was organized among ten different international institutions. The goal is to provide a consistent framework for the analysis of irradiated stainless steels using APT. Through the development of more reliable and reproducible data analysis and through communication, this project also aims to advance the understanding between irradiated microstructure and materials performance by providing more complete quantitative microstructural input for modeling. The results, methods, and findings of this round robin will also apply to other clustering phenomena studied using APT, beyond the theme of radiation damage.

Much effort has been devoted to the development of computational techniques in atom probe microscopy over the past decade. There have been several drivers for this effort. Firstly, there has been effort devoted to addressing the challenges of discerning information from the increasingly large size of the data, and capturing the opportunities that this large data presents. Secondly, there has been significant new effort devoted to the simulation of atom probe data so that pristine datasets that contain microstructural features of increasing complexity can be generated in-silico , and subjected to complex data-mining algorithms. This has enabled the benchmarking of various algorithms, guided the setting of parameters for particular analyses, and exposed the effects of instrumentation parameters such as detector efficiency and aberrations in ionic flight path. The authors are especially interested in the prospects of converging atomic-scale microscopy with atomic-scale materials modelling via first principles approaches. This involves excising parts of the APM data and using these as super-cell inputs to calculations of materials properties via density functional theory. It is our opinion that this represents a major advance for materials science because it enables microscopy to advance microstructure–property relationships to the direct mapping of such relationships based on many-body interactions. As such, this approach has great potential for materials design and development. The final part of this paper focuses on how cloud-based computing represents an exciting frontier of the computational aspects of atom probe microscopy. We discuss the opportunities and the barriers for conducting new materials science through the analysis and visualisation of atom probe data via new generation tools that are cloud-based, and which are managed, curated and governed with significant user-community input and integrated with contemporary electronic laboratory notebook technology.

Understanding the relationship between atomic-scale structure and properties is becoming increasingly critical as microstructures are now tailored at the nanometre length scale. Here we demonstrate 3-D mapping of grain orientations through atom probe tomography by utilizing Hough transforms to extract the orientation of crystallographic directions. The disorientation across boundaries is also determined. We are now able to combine the powerful capability of atom probe for measuring the 3-D distribution of atoms with the new ability to provide accurate crystallographic information. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

International audience

The mechanism of the increase in ductility in bulk metallic glass matrix composites over monolithic bulk metallic glasses is to date little understood, primarily because the interplay between dislocations in the crystalline phase and shear bands in the glass could neither be imaged nor modelled in a validated way. To overcome this roadblock, we show that shear bands can be imaged in three dimensions by atom probe tomography from density variations in the reconstructed atomic density, which density-functional theory suggests being a local-work function effect. Imaging of near-interface shear bands in Ti48 Zr20 V12 Cu5 Be15 bulk metallic glass matrix composite permits measurement of their composition, thickness, branching and interactions with the dendrite interface. These results confirm that shear bands here nucleate from stress concentrations in the glass due to intense, localized plastic deformation in the dendrites rather than intrinsic structural inhomogeneities.

The following manuscript presents a novel approach for creating lattice based models of Sb-doped Si directly from atom probe reconstructions for the purposes of improving information on dopant positioning and directly informing quantum mechanics based materials modeling approaches. Sophisticated crystallographic analysis techniques are used to detect latent crystal structure within the atom probe reconstructions with unprecedented accuracy. A distortion correction algorithm is then developed to precisely calibrate the detected crystal structure to the theoretically known diamond cubic lattice. The reconstructed atoms are then positioned on their most likely lattice positions. Simulations are then used to determine the accuracy of such an approach and show that improvements to short-range order measurements are possible for noise levels and detector efficiencies comparable with experimentally collected atom probe data.

Artefacts in atom probe tomography can impact the compositional analysis of microstructure in atom probe studies. To determine the integrity of information obtained, it is essential to understand how the positioning of features influences compositional analysis. By investigating the influence of feature orientation within atom probe data on measured composition in microstructural features within an AA2198 Al alloy, this study shows differences in the composition of T1 (Al2CuLi) plates that indicates imperfections in atom probe reconstructions. The data fits a model of an exponentially-modified Gaussian that scales with the difference in evaporation field between solutes and matrix. This information provides a guide for obtaining the most accurate information possible.

International audience; In this study, atom probe tomography was used to investigate the microstructure of the alloy AA2198 (Al-1.35 Cu-3.55 Li-0.29 Mg-0.08 Ag) over a range of ageing conditions to examine the evolution of phases in the alloy, in particular aiming to reveal the nucleation mechanism of the strengthening T-1 phase. T-1 precursor phases were observed from early ageing, most of which were connected to dislocations enriched with Mg and Ag. This Mg solute segregation on the dislocations was subsequently observed to develop into S-like phases. Ag and Mg segregation to T-1 interfaces was systematically observed when the plates were oriented perpendicular to the probing direction. The matrix solute content was followed during the course of T-1 precipitation. It was found that the evolution of Cu, Li, Mg and Ag was similar, giving additional evidence for their co-precipitation.

Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping.

Progress in the reconstruction for atom probe tomography has been limited since the first implementation of the protocol proposed by Bas et al. in 1995. This approach, and those subsequently developed, assume that the geometric parameters used to build the three-dimensional atom map are constant over the course of an analysis. Here, we test this assumption within the analyses of low-alloyed materials. By building upon methods recently proposed to measure the tomographic reconstruction parameters, we demonstrate that this assumption can introduce significant limitations in the accuracy of the analysis. Moreover, we propose a strategy to alleviate this problem through the implementation of a new reconstruction algorithm that dynamically accommodates variations in the tomographic reconstruction parameters., Comment: 16 pages, 6 figures