The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo2O5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo2O5+δ double perovskite was obtained by annealing cubic A-site cation disordered La0.5Ba0.5CoO3-δ perovskite at 1100 °C in N2. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo2O5+δ remains tetragonal during heating in oxidizing atmosphere, but goes through two phase transitions in N2 and between 450 °C and 675 °C from tetragonal P4/mmm to orthorhombic Pmmm and back to P4/mmm due to oxygen vacancy ordering followed by disordering of the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo2O5+δ was demonstrated. La0.5Ba0.5CoO3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo2O5+δ is metastable with respect to La0.5Ba0.5CoO3-δ at oxidizing conditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Co in the two materials. The oxidation state of Co is higher in La0.5Ba0.5CoO3-δ resulting in a higher electrical conductivity relative to LaBaCo2O5+δ. The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior.

Experiments are reported which show that currents of low energy ("cold") electrons pass unattenuated through crystalline ice at 135 K for energies between zero and 650 meV, up to the maximum studied film thickness of 430 bilayers, indicating negligible apparent trapping. By contrast, both porous amorphous ice and compact crystalline ice at 40 K show efficient electron trapping. Ice at intermediate temperatures reveals metastable trapping that decays within a few hundred seconds at 110 K. Our results are the first to demonstrate full transmission of cold electrons in high temperature water ice and the phenomenon of temperature-dependent trapping.

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Studying noninvasively the internal nanoporous structure of a single Tussah silk fiber under different humidity conditions, we demonstrate for the first time the feasibility of in-situ ptychographic tomography. The resulting 3D images of the silk fiber interior, obtained at both dry and humid conditions, yield quantitative information about the spatial density variations in the form of detailed maps of the size, shape, and orientation distributions of the nanopores inside the silk fiber, revealing that the fiber swells anisotropically in humid conditions, with the expansion taking place solely normal to the fiber axis. Exploiting quantitative information on the fiber’s electron density, hydration was found to proceed through interaction with the silk protein rather than filling of pores.

Cobalt nanoparticles play an important role as catalysts for the Fischer− Tropsch synthesis, which is an attractive route for production of synthetic fuels. It is of particular interest to understand the varying conversion rate during the first hours after introducing synthesis gas (H 2 and CO) to the system. To this end, several in situ characterization studies have previously been done on both idealized model systems and commercially relevant catalyst nanoparticles, using bulk techniques, such as X-ray powder diffraction and X-ray absorption spectroscopy. Since catalysis takes place at the surface of the cobalt particles, it is important to develop methods to gain surface-specific structural information under realistic processing conditions. We addressed this challenge using small-angle X-ray scattering (SAXS), a technique exploiting the penetrating nature of Xrays to provide information about particle morphology during in situ experiments. Simultaneous wide-angle X-ray scattering was used for monitoring the reduction from oxide to catalytically active metal cobalt, and anomalous SAXS was used for distinguishing the cobalt particles from the other phases present. After introducing the synthesis gas, we found that the slope of the scattered intensity in the Porod region increased significantly, while the scattering invariant remained essentially constant, indicating a change in the shape or surface structure of the particles. Shape-and surface change models are discussed in light of the experimental results, leading to an improved understanding of catalytic nanoparticles. ■ INTRODUCTIONThe Fischer−Tropsch synthesis (FTS) is a set of chemical reactions that forms hydrocarbon chains from a mixture of CO and H 2 . The product can be upgraded to petroleum substitutes, for example synthetic diesel.1 Typical commercial FTS catalysts consist of cobalt nanoparticles of diameter ∼20 nm dispersed on a porous support material, 2 such as γ-alumina. Optimal particle size, temperature, and pressure are required for obtaining high activity and high selectivity to long-chain hydrocarbons. The reaction output is dependent on the temperature and the pressure in the reactor cell; the standard industrial process operates at T ≈ 220°C and pressure of 25− 45 bar, conditions favorable for producing waxes.1 At ambient pressure the CO conversion is still high, but the products are predominantly short molecules, thus tending to remain in the gas phase.The FTS shows an initial stage lasting a few hours where the conversion rate increases to a high level, followed by a much slower decrease of the reaction rate that continues on a time scale of days and months.3 Understanding the mechanisms behind this behavior is of high commercial and academic interest. Tsakoumis et al.3 combined in situ X-ray absorption spectroscopy (XAS) and X-ray powder diffraction to investigate the cobalt catalyst nanoparticles during the FTS synthesis. The deactivation was detected by mass spectrometry, but no apparent changes in the X-ray signal could be...