Abstract: Bulk oxyfluoride glasses doped with Ag nanoclusters have been prepared using the melt quenching technique. When pumped in the absorption band of Ag nanoclusters between 300 to 500 nm, these glasses emit a very broad luminescence band covering all the visible range with a weak tail extending into the near infrared. The maximum of the luminescence band and its color shifts to the blue with a shortening of the excitation wavelength and an increasing ratio of oxide to fluoride components, resulting in white color luminescence at a particular ratio of oxide to fluoride; with a quantum yield above 20%.

Abstract: Nanocrystalline powders of undoped and lanthanide (Pr3+, Tm3+)- doped gadolinium gallium garnet, Gd3Ga5O12 (GGG), were prepared by propellant synthesis and studied by x-ray powder diffraction (XRD), electron diffraction (ED), high-resolution electron microscopy (HREM) and luminescence spectroscopy. The x-ray diffraction patterns of the GGG samples were analysed using the Rietveld method. The Rietveld refinement reveals the existence of two garnet-type phases: both are cubic (space group Ia $(3) over bar $d) with a slightly different lattice parameter and probably a slightly different composition. Electron diffraction and electron microscopy measurements confirm the x-ray diffraction results. EDX measurements for lanthanide-doped samples show that stable solid solutions with composition Gd(3-x)Ln(x)Ga(5)O(12), x approximate to 0.3 ( Ln = Pr; Tm) have been obtained. The luminescence properties of the Tm3+ -doped nanocrystalline GGG samples were measured and analysed.

Abstract: Hydrogen plays an essential role during the in situ assembly of tailored catalytic materials, and serves as key ingredient in multifarious chemical reactions promoted by these catalysts. Despite intensive debate for several decades, the existence and nature of hydrogen-involved mechanisms – such as hydrogen-spillover, surface migration – have not been unambiguously proven and elucidated up to date. Here, Pt-Ga alloy formation is used as a probe reaction to study the behavior and atomic transport of H and Ga, starting from Pt nanoparticles on hydrotalcite-derived Mg(Ga)(Al)Ox supports. In situ XANES spectroscopy, time-resolved TAP kinetic experiments, HAADF-STEM imaging and EDX mapping are combined to probe Pt, Ga and H in a series of H2 reduction experiments up to 650 degrees C. Mg(Ga)(Al)Ox by itself dissociates hydrogen, but these dissociated hydrogen species do not induce significant reduction of Ga3+ cations in the support. Only in the presence of Pt, partial reduction of Ga3+ into Gadelta+ is observed, suggesting that different reaction mechanisms dominate for Pt- and Mg(Ga)(Al)Ox-dissociated hydrogen species. This partial reduction of Ga3+ is made possible by Pt-dissociated H species which spillover onto non-reducible Mg(Al)Ox or partially reducible Mg(Ga)(Al)Ox and undergo long-range transport over the support surface. Moderately mobile Gadelta+Ox migrates towards Pt clusters, where Gadelta+ is only fully reduced to Ga0 on condition of immediate stabilization inside Pt-Ga alloyed nanoparticles.

Abstract: Reaching atomic resolution in 3D has been the ultimate goal in the field of electron tomography for many years. Significant progress, both on the theoretical as well as the experimental side has recently resulted in several exciting examples demonstrating the ability to visualise atoms in 3D. In this paper, we will review the different steps that have pushed the resolution in 3D to the atomic level. A broad range of methodologies and practical examples together with their impact on materials science will be discussed. Finally, we will provide an outlook and will describe future challenges in the field of high resolution electron tomography.

Abstract: Single crystals with two different morphologies, black and brown, of C60 with about 12% C70 have been studied by synchrotron X-ray diffraction. Integrated intensities from 8 reflections show that the charge distribution of the C60 cluster is shell-like giving rise to an oscillatory behaviour in the diffracted intensities. From the intensities, the distance between diametrically opposite carbon atoms has been determined to be (7.24 +/- 0.22) angstrom. The thickness of the charge distribution of the shell can be estimated as 3.06 angstrom and the cavity within a C60 cluster to have a diameter of about 4.18 angstrom. The finite longitudinal width of the diffraction peaks from black crystals indicates a lack of long-range crystalline order. The rocking curves are about 7-degrees broad and depict an unusually smooth behaviour. This may be indicative of a glassy or hexatic phase. High-resolution electron microscopy allows small crystallites with a relatively well-defined orientation relationship to be identified. In contrast, brown crystals have long-range order.

Abstract: Supported Fe2O3–TiO2 nanocomposites are fabricated by an original vapor phase synthetic strategy, consisting of the initial growth of Fe2O3 nanosystems on fluorine-doped tin oxide substrates by plasma enhanced-chemical vapor deposition, followed by atomic layer deposition of TiO2 overlayers with variable thickness, and final thermal treatment in air. A thorough characterization of the target systems is carried out by X-ray diffraction, atomic force microscopy, field emission-scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. High purity nanomaterials characterized by the co-presence of Fe2O3 (hematite) and TiO2 (anatase), with an intimate Fe2O3–TiO2 contact, are successfully obtained. In addition, photocatalytic tests demonstrate that, whereas both single-phase oxides do not show appreciable activity, the composite systems are able to degrade methyl orange aqueous solutions under simulated solar light, and even visible light, with an efficiency directly dependent on TiO2 overlayer thickness. This finding opens attractive perspectives for eventual applications in wastewater treatment.

Abstract: In this work we elucidate the elimination of mechanism Fe-antisite defects in lithium iron phosphate (LiFePO4) during the hydrothermal synthesis. Compelling evidence of this effect is provided by combining Neutron Powder Diffraction (NPD), High Resolution (Scanning) Transmission Electron Microscopy (HR-(S)TEM), Electron Energy Loss Spectroscopy (EELS), X-Ray Photoelectron Spectroscopy (XPS) and calculations. We found: i) the first intermediate vivianite inevitably creates Fe-antisite defects in LiFePO4; ii) the removal of these antisite defects by cation exchange is assisted by a nanometer-thick amorphous layer, rich in Li, that enwraps the LiFePO4 crystals.

Abstract: The three-dimensional (3D) distribution of carbon nanotubes (CNTs) grown inside semiconductor contact holes is studied by electron tomography. The use of a specialized tomography holder results in an angular tilt range of ±90°, which means that the so-called missing wedge is absent. The transmission electron microscopy (TEM) sample for this purpose consists of a micropillar that is prepared by a dedicated procedure using the focused ion beam (FIB) but keeping the CNTs intact. The 3D results are combined with energy dispersive X-ray spectroscopy (EDS) to study the relation between the CNTs and the catalyst particles used during their growth. The reconstruction, based on the full range of tilt angles, is compared with a reconstruction where a missing wedge is present. This clearly illustates that the missing wedge will lead to an unreliable interpretation and will limit quantitative studies

Abstract: Lithium-ion battery cathode materials have relied on cationic redox reactions until the recent discovery of anionic redox activity in Li-rich layered compounds which enables capacities as high as 300 mAh g(-1). In the quest for new high-capacity electrodes with anionic redox, a still unanswered question was remaining regarding the importance of the structural dimensionality. The present manuscript provides an answer. We herein report on a beta-Li2IrO3 phase which, in spite of having the Ir arranged in a tridimensional (3D) framework instead of the typical two-dimensional (2D) layers seen in other Li-rich oxides, can reversibly exchange 2.5 e(-) per Ir, the highest value ever reported for any insertion reaction involving d-metals. We show that such a large activity results from joint reversible cationic (Mn+) and anionic (O-2)(n-) redox processes, the latter being visualized via complementary transmission electron microscopy and neutron diffraction experiments, and confirmed by density functional theory calculations. Moreover, beta-Li2IrO3 presents a good cycling behaviour while showing neither cationic migration nor shearing of atomic layers as seen in 2D-layered Li-rich materials. Remarkably, the anionic redox process occurs jointly with the oxidation of Ir4+ at potentials as low as 3.4 V versus Li+/Li-0, as equivalently observed in the layered alpha-Li2IrO3 polymorph. Theoretical calculations elucidate the electrochemical similarities and differences of the 3D versus 2D polymorphs in terms of structural, electronic and mechanical descriptors. Our findings free the structural dimensionality constraint and broaden the possibilities in designing high-energy-density electrodes for the next generation of Li-ion batteries.

Abstract: Structural, chemical, and physical properties of whitlockite-type Ca9Bi(VO4)(7) were studied by X-ray powder diffraction (XRD), electron diffraction (ED), second-harmonic generation (SHG), thermogravimetry, differential scanning calorimetry, dielectric, and electrical-conductivity measurements. A new phase-transition of the ferroelectric type was found in Ca9Bi(VO4)(7) with a transition temperature, T-c of 1053 +/- 3 K. The polar phase, beta-Ca9Bi(VO4)(7), is stable below T-c down to at least 160 K. The centrosymmetric beta'-phase is stable above T-c up to 1273 +/- 5 K. Above 1273 K, it decomposes to give BiVO4 and whitlockite-type solid solutions of Ca9+1.5xBi1-x(VO4)(7). The beta<---->beta' phase transition is reversible and of second order. Electrical conductivity of beta'-Ca9Bi(VO4)(7) is rather high (sigma = 0.6 x 10(-3) S/cm at 1200 K) and obeys the Arrhenius law with an activation energy of 1.0 eV. Structure parameters of Ca9Bi(VO4)(7) are refined by the Rietveld method from XRD data measured at room temperature (space group R3c; Z = 6; a = 10.8992(1) Angstrom, c = 38.1192(4) Angstrom, and V = 3921.6(1) Angstrom(3); R-wp = 3.06% and R-p = 2.36%). Bi3+ ions together with Ca2+ ions are statistically distributed among the M1, M2, M3, and M5 sites. Ca9Bi(VO4)(7) has a SHG efficiency of about 140 times that of quartz. Through the powder SHG measurements, we estimated the nonlinear optical susceptibility, Digital, at about 6.1-7.2 pm/V. This value for Ca9Bi(VO4)(7) is comparable with that for known nonlinear optical materials such as LiNbO3 and LiTaO3.