Abstract: The toughness of Al-to-steel welds decreases with increasing thickness of the intermetallic (IM) layer formed at the interface. Co plating has been added as interlayer in Al-to-steel Friction Melt Bonded (FMB) welds to control the nature and thickness of the IM layer. In comparison to a weld without interlayer, Co plating brings about a reduction of the thickness of the IM layer by 70%. The critical energy release rate of the crack propagating in the weld is used as an indicator of toughness. It is evaluated via an adapted crack propagation test using an energy conservation criterion. For a weld without interlayer, critical energy release rate is found to increase when the thickness of the intermetallic layer decreases. When the intermetallic layer is thick, the crack propagates in a brittle manner through the intermetallic whereas, at low layer thickness, the crack deviates and partially propagates through the Al plate, which causes an increase of toughness. The use of a Co interlayer brings about an increase of toughness by causing full deviation of the crack towards the Al plate.

Abstract: Rational synthesis of nanowires via the vaporliquidsolid (VLS) mechanism with compositional and structural controls is vitally important for fabricating functional nanodevices from bottom up. Here, we show that branched indium tin oxide nanowires can be in situ seeded in vapor transport growth using tailored AuCu alloys as catalyst. Furthermore, we demonstrate that VLS synthesis gives unprecedented freedom to navigate the ternary InSnO phase diagram, and a rare and bulk-unstable cubic phase can be selectively stabilized in nanowires. The stabilized cubic fluorite phase possesses an unusual almost equimolar concentration of In and Sn, forming a defect-free epitaxial interface with the conventional bixbyite phase of tin-doped indium oxide that is the most employed transparent conducting oxide. This rational methodology of selecting phases and making abrupt axial heterojunctions in nanowires presents advantages over the conventional synthesis routes, promising novel composition-modulated nanomaterials.

Abstract: Ni4Ti3 precipitates play an important role in the shape memory and superelastic behaviour of thermo-mechanically treated Ni-Ti material. The 3D morphology and distribution of such precipitates with lenticular shape and rhombohedral atomic structure in the austenitic B2 matrix of a binary Ni-rich Ni-Ti alloy has been elucidated via a slice view procedure in a Dual-Beam FIB/SEM system. With the sequence of cross-section SE images obtained from the SEM, a 3D reconstruction has been achieved after proper alignment and image processing, from which both qualitative and quantitative analysis can be performed. Careful imaging is needed to ensure that all variants of the precipitates are observed with equal probability, regardless sample orientation. Moreover, due to the weak contrast of the precipitates, proper imaging conditions need to be selected to allow for semi-automated image treatment. Finally, a volume ratio of 10.2% for the Ni4Ti3 precipitates could be calculated, summed over all variants, which yields a net composition of Ni50.36Ti49.64 for the matrix, leading to an increase of 113 degrees for the martensitic start temperature Ms. Also, the expected relative orientation of the different variants of the precipitates could be confirmed. In the near future, other quantitative measures on the distribution of the precipitates can be expected.

Abstract: The occurrence and origin of diffuse intensity contours in electron micrographs of AgBr crystals are investigated. The observations are interpreted in terms of a model, which attributes diffuse scattering to the presence of predominant atom or vacancy clusters of a particular polyhedral type. It is shown that irrespective of the crystal morphology, interstitial Ag ions order in AgBr material in clusters of finite size along 001 type planes. A different geometry of the diffuse intensity locus observed for triangular and hexagonal tabular grains is explained in terms of the different twin plane morphology of these grains.

Abstract: The double phosphate Ca9In(PO4)(7) was obtained by solid-state reaction and was studied by room and high-temperature Xray powder diffraction, electron diffraction, high-resolution electron microscopy, second-harmonic generation (SHG) technique, differential scanning calorimetry, dielectric and conductivity measurements. The beta-Ca9In(PO4)(7) room-temperature phase is related to the mineral whitlockite and is similar to beta-Ca-3(PO4)(2). It has space group R (3) over barc, with unit cell parameters: a = 10.4008(1) Angstrom, c = 37.272(1) Angstrom, Z = 6. The structure was refined by the Rietveld method (R-wp = 4.69, R-I = 1.81). A reversible first-order beta <----> beta' phase transition of the ferroelectric type with T-c = 902 K is revealed by SHG, differential scanning calorimetry and dielectric measurements. The centrosymmetric beta'-Ca9In(PO4)(7) (973 K) has space group R (3) over barc, a = 10.4611(2) Angstrom, c = 37.874 (1) Angstrom (R-wp = 4.27, R-I = 4.11). Compared to the low-temperature beta-Ca9In(PO4)(7) structure, beta'-Ca9In(PO4)(7) can be described as an orientational disordering of the P1O(4) tetrahedra together with a calcium disordering on the M3 site. (C) 2002 Elsevier Science (USA).

Abstract: Diamond is a promising material for a number of bio-applications, including the fabrication of platforms for attachment and investigation of neurons and of neuroprostheses, such as retinal implants. In the current work ultrananocrystalline diamond (UNCD) films were deposited by microwave plasma chemical vapor deposition, modified by UV/O-3 treatment or NH3 plasma, and comprehensively characterized with respect to their bulk and surface properties, such as crystallinity, topography, composition and chemical bonding nature. The interactions of insect circadian pacemaker neurons with UNCD surfaces with H-, O- and NH2-terminations were investigated with respect to cell density and viability. The fast and strong attachment achieved without application of adhesion proteins allowed for advantageous modification of dispersion protocols for the preparation of primary cell cultures. Centrifugation steps, which are employed for pelletizing dispersed cells to separate them from dispersing enzymes, easily damage neurons. Now centrifugation can be avoided since dispersed neurons quickly and strongly attach to the UNCD surfaces. Enzyme solutions can be easily washed off without losing many of the dispersed cells. No adverse effects on the cell viability and physiological responses were observed as revealed by calcium imaging. Furthermore, the enhanced attachment of the neurons, especially on the modified UNCD surfaces, was especially advantageous for the immunocytochemical procedures with the cell cultures. The cell losses during washing steps were significantly reduced by one order of magnitude in comparison to controls. In addition, the integration of a titanium grid structure under the UNCD films allowed for individual assignment of physiologically characterized neurons to immunocytochemically stained cells. Thus, employing UNCD surfaces free of foreign proteins improves cell culture protocols and immunocytochemistry with cultured cells. The fast and strong attachment of neurons was attributed to a favorable combination of topography, surface chemistry and wettability. (C) 2016 Elsevier B.V. All rights reserved.

Abstract: The ESTEEM consortium of electron microscopy laboratories for materials science and solid-state physics has been created as an EU-supported delocalized infrastructure (I3) to bring together the major electron microscopy centres in Europe. Its main objectives were to develop networking, to offer transnational access to these centres with specialized and complementary techniques and skills and to upgrade in close collaboration different technical and methodological aspects such as tomography, spectroscopy, holography, detectors, and specimen holders. These efforts were aimed to strengthen the position of European microscopy and to generate new technologies potentially of high relevance in many domains identified as strategic. Following the success of the first program, ESTEEM has been reconducted in 2012 for four more years with an enlarged set of partners.

Abstract: Superelastic deformation of thin NiTi wires containing various nanograined microstructures was investigated by tensile cyclic loading with in situ evaluation of electric resistivity. Defects created by the superelastic cycling in these wires were analyzed by transmission electron microscopy. The role of dislocation slip in superelastic deformation is discussed. NiTi wires having finest microstructures (grain diameter <100 nm) are highly resistant against dislocation slip, while those with fully recrystallized microstructure and grain size exceeding 200 nm are prone to dislocation slip. The density of the observed dislocation defects increases significantly with increasing grain size. The upper plateau stress of the superelastic stressstrain curves is largely grain size independent from 10 up to 1000 nm. It is hence claimed that the HallPetch relationship fails for the stress-induced martensitic transformation in this grain size range. It is proposed that dislocation slip taking place during superelastic cycling is responsible for the accumulated irreversible strains, cyclic instability and degradation of functional properties. No residual martensite phase was found in the microstructures of superelastically cycled wires by TEM and results of the in situ electric resistance measurements during straining also indirectly suggest that none or very little martensite phase remains in the studied cycled superelastic wires after unloading. The accumulation of dislocation defects, however, does not prevent the superelasticity. It only affects the shape of the stressstrain response, makes it unstable upon cycling and changes the deformation mode from localized to homogeneous. The activity of dislocation slip during superelastic deformation of NiTi increases with increasing test temperature and ultimately destroys the superelasticity as the plateau stress approaches the yield stress for slip. Deformation twins in the austenite phase ({1 1 4} compound twins) were frequently found in cycled wires having largest grain size. It is proposed that they formed in the highly deformed B19′ martensite phase during forward loading and are retained in austenite after unloading. Such twinning would represent an additional deformation mechanism of NiTi yielding residual irrecoverable strains.

Abstract: Ultrathin two-dimensional (2D) nanosheets (NSs) possess extraordinary properties that are attractive for both fundamental studies and technological devices. Solution-based bottom-up methods are emerging as promising routes to produce free-standing NSs, but the synthesis of colloidal NSs with well-defined size and shape has remained a major challenge. In this work, we report a novel method that yields 2 nm thick colloidal Cu2-xS NSs with well-defined shape (triangular or hexagonal) and size (100 nm to 3 mu m). The key feature of our approach is the use of a synergistic interaction between halides (Br or Cl) and copper-thiolate metal-organic frameworks to create a template that imposes 2D constraints on the Cu-catalyzed C-S thermolysis, resulting in nucleation and growth of colloidal 2D Cu2-xS NSs. Moreover, the NS composition can be postsynthetically tailored by exploiting topotactic cation exchange reactions. This is illustrated by converting the Cu2-xS NSs into ZnS and CdS NSs while preserving their size and shape. The method presented here thus holds great promise as a route to solution-processable compositionally diverse ultrathin colloidal NSs with well-defined shape and size.

Abstract: The evolution of the uranium chemical state in uranium compounds, principally in the oxides, is of concern in the context of nuclear fuel degradation under storage and repository conditions, and in accident scenarios. The U–O system shows complicated phase relations between single-valence uranium dioxide (UO₂) and different mixed-valence compounds (<italic>e.g.</italic>U₄O₉, U₃O₇and U₃O₈). To try resolving the electronic structure associated with unique atomic positions, a combined application of diffraction and spectroscopic techniques, such as diffraction anomalous fine structure (DAFS), can be considered. Reported here is the application of two newly developed routines for assessing a DAFS data set, with the aim of refining the uranium X-ray dispersion corrections. High-resolution anomalous diffraction data were acquired from polycrystalline powder samples of UO₂(containing tetravalent uranium) and potassium uranate (KUO₃, containing pentavalent uranium) using synchrotron radiation in the vicinity of the U<italic>L</italic>₃edge (17.17 keV). Both routines are based on an iterative refinement of the dispersion corrections, but they differ in either using the intensity of a selection of reflections or doing a full-pattern (Rietveld method) refinement. The uranium dispersion corrections obtained using either method are in excellent agreement with each other, and they show in great detail the chemical shifts and differences in fine structure expected for tetravalent and pentavalent uranium. This approach may open new possibilities for the assessment of other, more complicated, materials such as mixed-valence compounds. Additionally, the DAFS methodology can offer a significant resource optimization because each data set contains both structural (diffraction) and chemical (spectroscopy) information, which can avoid the requirement to use multiple experimental stations at synchrotron sources.

Abstract: The (1 − x)BiFeO3−xLaFeO3 system has been investigated and characterized by room-temperature and high-temperature laboratory and synchrotron powder X-ray diffraction, electron diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. At room temperature, the ferroelectric R3c phase is observed for 0.0 ≤ x ≤ 0.10. The PbZrO3-related √2ap × 2√2ap × 4ap superstructure (where ap is the parameter of the cubic perovskite subcell) is observed for Bi0.82La0.18FeO3, while an incommensurately modulated phase is formed for 0.19 ≤ x ≤ 0.30 with the √2ap × 2ap × √2ap basic unit cell. The GdFeO3-type phase with space group Pnma (√2ap × 2ap × √2ap) is stable at 0.50 ≤ x ≤ 1. Bi0.82La0.18FeO3 has no detectable homogeneity range (space group Pnam, a = 5.6004(1) Å, b = 11.2493(3) Å, c = 15.6179(3) Å). The incommensurately modulated Bi0.75La0.25FeO3 structure was solved from synchrotron X-ray powder diffraction data (Imma(00γ)s00 superspace group, a = 5.5956(1) Å, b = 7.8171(1) Å, c = 5.62055(8) Å, q = 0.4855(4)c*, RP = 0.023, RwP = 0.033). In this structure, cooperative displacements of the Bi and O atoms occur, which order within the (AO) (where A = Bi, La) layers, resulting in an antipolar structure. Local fluctuations of the intralayer antipolar ordering are compensated by an interaction with the neighboring (AO) layers. A coupling of the antipolar displacements with the cooperative tilting distortion of the perovskite octahedral framework is proposed as the origin of the incommensurability. All the phases transform to the GdFeO3-type structure at high temperatures. Bi0.82La0.18FeO3 shows an intermediate PbZrO3-type phase with √2ap × 2√2ap × 2ap (space group Pbam; a = 5.6154(2) Å, b = 11.2710(4) Å, and c = 7.8248(2) Å at 570 K). The compounds in the compositional range of 0.18 ≤ x ≤ 0.95 are canted antiferromagnets.

Abstract: We present an in situ transmission electron microscopy study on the half-doped bilayer manganite PrCa2Mn2O7 to reveal the rotation process of the orbital stripes. Between the reported initial and final ordering phases, we identified an intermediate state with two sets of satellite spots to bridge the 90° rotation of the orbital stripes. Furthermore, we determined that the rotation of the orbital stripes does not always occur. Some restricted conditions for the orbital rotation to occur were found and reasons are discussed.