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To elucidate the role of earth alkaline doping in perovskite-based dry reforming of methane (DRM) catalysts, we embarked on a comparative and exemplary study of a Ni-based Sm perovskite with and without Sr doping. While the Sr-doped material appears as a structure-pure Sm1.5Sr0.5NiO4 Ruddlesden Popper structure, the undoped material is a NiO/monoclinic Sm2O3 composite. Hydrogen pre-reduction or direct activation in the DRM mixture in all cases yields either active Ni/Sm2O3 or Ni/Sm2O3/SrCO3 materials, with albeit different short-term stability and deactivation behavior. The much smaller Ni particle size after hydrogen reduction of Sm1.5Sr0.5NiO4, and of generally all undoped materials stabilizes the short and long-term DRM activity. Carbon dioxide reactivity manifests itself in the direct formation of SrCO3 in the case of Sm1.5Sr0.5NiO4, which is dominant at high temperatures. For Sm1.5Sr0.5NiO4, the CO : H2 ratio exceeds 1 at these temperatures, which is attributed to faster direct carbon dioxide conversion to SrCO3 without catalytic DRM reactivity. As no Sm2O2CO3 surface or bulk phase as a result of carbon dioxide activation was observed for any material - in contrast to La2O2CO3 - we suggest that oxy-carbonate formation plays only a minor role for DRM reactivity. Rather, we identify surface graphitic carbon as the potentially reactive intermediate. Graphitic carbon has already been shown as a crucial reaction intermediate in metal-oxide DRM catalysts and appears both for Sm1.5Sr0.5NiO4 and NiO/monoclinic Sm2O3 after reaction as crystalline structure. It is significantly more pronounced for the latter due to the higher amount of oxygen-deficient monoclinic Sm2O3 facilitating carbon dioxide activation. Despite the often reported beneficial role of earth alkaline dopants in DRM catalysis, we show that the situation is more complex. In our studies, the detrimental role of earth alkaline doping manifests itself in the exclusive formation of the sole stable carbonated species and a general destabilization of the Ni/monoclinic Sm2O3 interface by favoring Ni particle sintering.

Noble metal nanoparticles anchored on flexible polyurethane foams were synthesized by hydrothermal synthesis. Through employing a robotic arm, these ‘catalytic sponges’ were used for organic reductions towards automated lab-scale organic synthesis.

Based on the recent interest in oxy-carbide materials in catalysis, we employ a thin film model concept to highlight that variation of key reaction parameters in the reactive magnetron sputtering of zirconium carbide films (sputtering power, template temperature or reactive plasma environment) under realistic preparation and application conditions often results in zirconium oxy-carbide films of varying stoichiometry. The composition of the films grown on silicon wafers and in vacuo - cleaved NaCl (001) single crystal facets was confirmed by depth profiling X-ray photoelectron spectroscopy and electron microscopy analysis. A correlation between methane-to-argon ratio, excess carbon and template temperature with elemental composition emphasizes the exclusive presence of oxygen-containing zirconium carbides. To generalize the approach, we also show that embedding of highly ordered Cu particles with uniform sizes in zirconium oxy-carbide matrices yields well-defined metal / oxy-carbide interfaces. As the presence of an oxy-carbide and its reactivity has been inextricably linked to enhanced activity and selectivity in a variety of processes, including hydrogenation, oxidation or reduction reactions, our model thin film approach provides the necessary well-defined catalysts to derive mechanistic details and to study the decomposition/re-carburization cycles of oxy-carbides. We have exemplified the concept for zirconium oxy-carbide, but deliberate extension to similar systems is easily possible.

In the challenging project concerning the realization of the CERN Future Circular Collider (FCC), Nb3Sn represents the best candidate material for the construction of high-field superconducting dipole magnets, since it is able to satisfy the requirements of Jc (non-Cu) = 1.5 kA/mm2 at 16 T and 4.2 K. In that context, a cluster layout of prototype internal tin Nb3Sn wires, developed by TVEL and the Bochvar Institute (Russia), was analyzed and compared to a standard layout produced by the same manufacturer. The main reason for dividing the sub-element into clusters is reducing the effective sub-element size (deff). The microstructural characterization of such a wire layout can provide fundamental contributions to steer the manufacturing processes towards higher performing wires. In particular, since the homogeneity in Sn concentration influences the superconducting properties, the effect of cluster and standard layouts on the Sn concentration gradient over the wire cross-section was evaluated. For this purpose, energy dispersive X-ray (EDX) spectroscopy was employed with both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Finally, scanning Hall probe microscopy (SHPM) measurements were performed to understand how these cluster wire sub-elements, with their specific geometry, influence the local currents flowing through the wire cross-section on a microscopic scale. The comprehension of the correlation between the microstructural characteristics and superconducting performance is crucial for obtaining wires meeting the requirements of FCC dipole magnets.

Imaging reactions across facets Metal nanoparticles used in heterogeneous catalysis can bear different facets with different reaction kinetics. Suchorski et al. used field electron microscopy with high spatial (∼2 nanometers) and time (∼2 milliseconds) resolution to study hydrogen oxidation on a curved rhodium crystal that displayed individual nanofacets. They also performed field ion microscopy of the water products. Periodic formation and depletion of subsurface oxygen blocked or allowed hydrogen adsorption, respectively, and led to oscillatory kinetics that could frequency lock between facets but at different frequencies. Surface reconstructions could also induce collapse of spatial coupling of oscillations. Science , abf8107, this issue p. 1314

The kinetic behavior of individual Rh(

The development of novel light metal alloys represents an important task in the further optimization of technical materials. Multi-component systems with more than 4 metals are very promising to outperform currently existing alloys, but lack significant research in systems not dominated by transition metals to date. In this work, alloys containing the elements Al, Cu, Mg and Zn were produced using magnetron sputter deposition. A detailed structural investigation using electron microscopy provided valuable insights into the influences of different metals and their relative proportions in the alloy on material properties.

To compare the inherent methanol steam reforming properties of intermetallic compounds and a corresponding intermetallic compound-oxide interface, we selected the Cu-In system as a model to correlate the stability limits, self-activation and redox activation properties with the catalytic performance. Three distinct intermetallic Cu-In compounds - Cu7In3, Cu2In and Cu11In9 - were studied both in an untreated and redox-activated state resulting from alternating oxidation-reduction cycles. The stability of all studied intermetallic compounds during methanol steam reforming (MSR) operation is essentially independent of the initial stoichiometry and all accordingly resist substantial structural changes. The inherent activity under batch MSR conditions is highest for Cu2In, corroborating the results of a Cu2In/In2O3 sample accessed through reactive metal-support interaction. Under flow MSR operation, Cu7In3 displays considerable deactivation, while Cu2In and Cu11In9 feature stable performance at simultaneously high CO2 selectivity. The missing significant self-activation is most evident in the operando thermogravimetric experiments, where no oxidation is detected for any of the intermetallic compounds. In situ X-ray diffraction allowed us to monitor the partial decomposition and redox activation of the Cu-In intermetallic compounds into Cu0.9In0.1/In2O3 (from Cu7In3), Cu7In3/In2O3 (from Cu2In) and Cu7In3/Cu0.9In0.1/In2O3 (from Cu11In9) interfaces with superior MSR performance compared to the untreated samples. Although the catalytic profiles appear surprisingly similar, the latter interface with the highest indium content exhibits the least deactivation, which we explain by formation of stabilizing In2O3 patches under MSR conditions.

The influence of A- and/or B-site doping of Ruddlesden-Popper perovskite materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of specific A2BO4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room temperature, B-site doping of La2NiO4 with Cu stabilizes the orthorhombic structure (Fmmm) of the perovskite, while A-site doping with Ba yields a tetragonal space group (I4/mmm). We observed the orthorhombic-to-tetragonal transformation above 170 °C for La2Ni0.9Cu0.1O4 and La2Ni0.8Cu0.2O4, slightly higher than for undoped La2NiO4. Loss of oxygen in interstitial sites of the tetragonal structure causes further structure transformations for all samples before decomposition in the temperature range of 400 °C-600 °C. Controlled in situ decomposition of the parent or A/B-site doped perovskite structures in a DRM mixture (CH4:CO2 = 1:1) in all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in contact with hexagonal La2O3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La2O2CO3, BaCO3). Differences in the catalytic activity evolve because of (i) the in situ formation of Ni-Cu alloy phases (in a composition of >7:1 = Ni:Cu) for La2Ni0.9Cu0.1O4, La2Ni0.8Cu0.2O4, and La1.8Ba0.2Ni0.9Cu0.1O4, (ii) the resulting Ni particle size and amount of exsolved Ni, and (iii) the inherently different reactivity of the present (oxy)carbonate species. Based on the onset temperature of catalytic DRM activity, the latter decreases in the order of La2Ni0.9Cu0.1O4 ∼ La2Ni0.8Cu0.2O4 ≥ La1.8Ba0.2Ni0.9Cu0.1O4 > La2NiO4 > La1.8Ba0.2NiO4. Simple A-site doped La1.8Ba0.2NiO4 is essentially DRM inactive. The Ni particle size can be efficiently influenced by introducing Ba into the A site of the respective Ruddlesden-Popper structures, allowing us to control the Ni particle size between 10 nm and 30 nm both for simple B-site and A-site doped structures. Hence, it is possible to steer both the extent of the metal-oxide-(oxy)carbonate interface and its chemical composition and reactivity. Counteracting the limitation of the larger Ni particle size, the activity can, however, be improved by additional Cu-doping on the B-site, enhancing the carbon reactivity. Exemplified for the La2NiO4 based systems, we show how the delicate antagonistic balance of doping with Cu (rendering the La2NiO4 structure less stable and suppressing coking by efficiently removing surface carbon) and Ba (rendering the La2NiO4 structure more stable and forming unreactive surface or interfacial carbonates) can be used to tailor prospective DRM-active catalysts.

Following the need for an innovative catalyst and material design in catalysis, we provide a comparative approach using pure and Pd-doped LaCu

Accelerating the oxygen reduction kinetics of solid oxide fuel cell (SOFC) cathodes is crucial to improve their efficiency and thus to provide the basis for an economically feasible application of intermediate temperature SOFCs. In this work, minor amounts of Pt were doped into lanthanum strontium ferrite (LSF) thin film electrodes to modulate the material's oxygen exchange performance. Surprisingly, Pt was found to be incorporated on the B-site of the perovskite electrode as non metallic Pt

Author(s): Ploner, K; Delir Kheyrollahi Nezhad, P; Watschinger, M; Schlicker, L; Bekheet, MF; Gurlo, A; Gili, A; Doran, A; Schwarz, S; Stoger-Pollach, M; Bernardi, J; Armbruster, M; Klotzer, B; Penner, S | Abstract: On Cu/ZrO2 catalysts, variation of the Cu loading from 0.2 wt% to 80 wt% allows assessing the influence of the Cu-ZrO2 interface on the methanol steam reforming (MSR) performance by steering Cu particle size and morphology, revealing the contribution of potential active sites at the interface and the intrinsic relative contributions of the support and Cu surface fraction. As ZrO2 influences both CO2-selective and selectivity-spoiling MSR reaction channels, disentangling support-specific effects from the special phase-boundary reactivity and the intrinsic Cu° reactivity is possible by our approach. By choosing a broad range of Cu loadings, a comparison of the most extreme cases of strong predominance of bulk-like Cu sites (80 wt% Cu) vs. highly dispersed Cu (0.2 wt%), dominated by interfacial and support reactivity, becomes accessible. Cu (80 wt%)/ZrO2 evolves as the best MSR catalyst by avoiding adverse support effects and providing a high number of support-wetting bulk-like Cu sites.

Quantitative in situ X-ray diffraction in combination with catalytic tests in dry reforming of methane (DRM) has been performed to unveil the strong structural dynamics of LaNiO3 catalysts during t...

To evaluate the structural and spectroscopic steering factors of noble metal promotion in the catalytic reduction of NO by CO, a series of La(Cu0.7Mn0.3)0.98M0.02O3−δ (M = Pd, Pt, Ru, Rh) perovskite catalysts is investigated. The materials are synthesized by a sol-gel method and characterized by X-ray powder diffraction (XRD), electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). All metal-promoted perovskites exhibit a comparatively higher activity for catalytic reduction of NO by CO with respect to pure La(Cu0.7Mn0.3)O3−δ . Among all catalysts tested, the La(Cu0.7Mn0.3)0.98Pd0.02O3−δ perovskite shows the highest catalytic activity, which is tentatively related to a combined synergistic effect of improved oxygen vacancy activity and noble metals. Additionally, the redox chemistry of the catalysts in different reducing (H2) and oxidizing (NO, O2) atmospheres is tested. An enhanced kinetic reducibility, especially with Pd, was observed. All the H2-reduced catalysts are capable of reducing NO. At low and intermediate temperatures, the formation of N2O is observed, but at higher temperatures NO is exclusively converted to N2. The introduction of noble metals leads to new adsorption sites for NO. As XPS suggests a tendency for depletion of noble metals in the surface-near regions, while the catalytic activity in NO reduction at the same time appears much improved, directed noble metal promotion with modest amounts especially in surface-near regions during synthesis appears as an encouraging method to economize the use of the latter. This work was performed within the framework of the funding programme IMPULSE Iran Austria, financed by funds of the OeAD fonds and of the Ministry of Science, Research and Technology of the Islamic Republic of Iran. We also thank the SFB F45-N16 special research program for financial support. This work was performed within the framework of the research platform ‘‘Materials and Nanoscience” and the special PhD program ‘‘Reactivity and Catalysis”, both at the University of Innsbruck.

In contrast to Co3O4, CoO has been much less studied for CO oxidation. Herein, the phase changes of commercial mesoscopic CoO (particle size ˜1 μm) and nanosized CoO (20–50 nm particle size), the latter prepared by vacuum reduction of commercial Co3O4, were examined by operando X-ray absorption (XAS) and near-ambient pressure X-ray photoemission (NAP-XPS) spectroscopy during CO oxidation, as well as ex situ by transmission electron microscopy and diffraction (TEM/SAED). Commercial mesoscopic CoO exhibited CO oxidation activity at ˜200 °C, but even up to 530 °C in pure O2 no substantial (bulk) oxidation was observed by operando XAS, likely due to the large grains and bulk nature of CoO. After pre-oxidation at 400 C, electron diffraction detected thin surface layers of Co3O4. This increased activity but the activity of nanosized Co3O4 of equal surface area was still not reached. For nanosized CoO (surface layers on vacuum-reduced Co3O4), operando NAP-XPS/XAS, acquired during CO oxidation, revealed oxidation of CoO to Co3O4 above 150 °C, yielding the activity of nanosized Co3O4. Evidently, the nanoscale CoO shell on a Co3O4 core with small grains more easily and more completely transformed to Co3O4 than mesoscopic (bulk) CoO with large grains. Our study demonstrates how flexible and dynamic surfaces of cobalt oxide materials adjust to various reaction environments, which also depends on grain size and morphology (bulk vs. thin layers), illustrating the importance of operando techniques to determine active catalyst phases under reaction conditions.

Identification and manipulation of transition-metal ion impurities in oxide nanoparticles require an in-depth understanding of their stability, segregation behavior, and, at the same time, knowledge about their surface reactivity. Powders of magnesium oxide nanoparticles with admixtures of iron or cobalt ions, as two next neighbors in the periodic table, were synthesized in the gas phase via injection of metal–organic precursors into the magnesium combustion flame followed by temperature quenching of resulting nanocrystals in argon. In these model systems of cubic nanocrystals, we explored the distinct stability of these impurities in great detail. While Co2+ ions keep their divalent valence state and substitute the host ions in the cationic sublattice, Fe3+ ions emerge due to the energy gain provided by charge compensation and impurity–vacancy complex formation. The very different behavior of Co and Fe ions in the MgO host lattice, their changes in the local environment, and the different trends in segre...

Highly oriented Ge 0.81Sn 0.19 nanowires have been synthesized by a low-temperature chemical vapor deposition growth technique. The nanostructures form by a self-seeded vapor-liquid-solid mechanism. In this process, liquid metallic Sn seeds enable the anisotropic crystal growth and act as a sole source of Sn for the formation of the metastable Ge 1-xSn x semiconductor material. The strain relaxation for a lattice mismatch of ϵ = 2.94% between the Ge (111) substrate and the constant Ge 0.81Sn 0.19 composition of nanowires is confined to a transition zone of 1-xSn x structures with diameters in the micrometer range show a 5-fold longer compositional gradient very similar to epitaxial thin-film growth. Effects of the Sn growth promoters' dimensions on the morphological and compositional evolution of Ge 1-xSn x are described. The temperature- and laser power-dependent photoluminescence analyses verify the formation of a direct band gap material with emission in the mid-infrared region and values expected for unstrained Ge 0.81Sn 0.19 (e.g., band gap of 0.3 eV at room temperature). These materials hold promise in applications such as thermal imaging and photodetection as well as building blocks for group IV-based mid- to near-IR photonics.

Direct ethanol fuel cells are highly promising energy conversion devices, but the complete oxidation of ethanol to CO2 at low temperatures is still one of the main challenges. Titanium oxycarbide (TiO1-xCx) powder is investigated as stable and synergistic support for Pt nanoparticles during the ethanol oxidation reaction (EOR) in acidic electrolytes. EOR products are quantitatively detected online with differential electrochemical mass spectrometry. At room temperature, Pt/TiO1-xCx has a CO2 efficiency maximum of 8.9%, while only 1.7% are measured for Pt nanoparticles on Vulcan carbon (Pt/C). The reaction pathway is channeled towards the formation of C1 products, while C2 product formation is suppressed. This effect is expected to be much enhanced at elevated temperatures which makes TiO1-xCx a highly interesting catalyst support material in general.

The reactive metal-support interaction in the Cu-In2O3 system and its implications on the CO2 selectivity in methanol steam reforming (MSR) have been assessed using nanosized Cu particles on a powdered cubic In2O3 support. Reduction in hydrogen at 300 °C resulted in the formation of metallic Cu particles on In2O3. This system already represents a highly CO2-selective MSR catalyst with ~93% selectivity, but only 56% methanol conversion and a maximum H2 formation rate of 1.3 µmol gCu−1 s−1. After reduction at 400 °C, the system enters an In2O3-supported intermetallic compound state with Cu2In as the majority phase. Cu2In exhibits markedly different self-activating properties at equally pronounced CO2 selectivities between 92% and 94%. A methanol conversion improvement from roughly 64% to 84% accompanied by an increase in the maximum hydrogen formation rate from 1.8 to 3.8 µmol gCu−1 s−1 has been observed from the first to the fourth consecutive runs. The presented results directly show the prospective properties of a new class of Cu-based intermetallic materials, beneficially combining the MSR properties of the catalyst’s constituents Cu and In2O3. In essence, the results also open up the pathway to in-depth development of potentially CO2-selective bulk intermetallic Cu-In compounds with well-defined stoichiometry in MSR., Graphical abstract

High efficiency, increasing power densities, lower weight and pollution reduction require new materials for combustion engine components in order to withstand the higher thermo-mechanical loads. Cast Al-Si alloys are used for cylinder heads where they combine light weight, good castability and suitable mechanical properties. Despite casting difficulties and their vulnerability to hot tearing these Al-Cu alloys can be used as candidates to achieve even better mechanical properties at elevated temperatures. These alloys are formed by a ductile precipitation hardening α-Al matrix and brittle intermetallics, mostly Al2Cu. Tensile deformation of AlCu4 as cast and AlCu7 solutionized and aged conditions is investigated by combined application of non-destructive testing and imaging methods (using electron, neutron and synchrotron radiation) to study the stress distribution between the Al2Cu structures and the surrounding Al matrix. The external loads are transferred into the microstructure by strain control due to percolating eutectic structures in AlCu4 and AlCu7 as cast. Homogenization by solution treatment and age hardening significantly increases the strength, although stress controlled behavior becomes dominant. (Some damage tolerance is observed in the as cast as well as in the heat treated condition, as load is transferred from particles which were broken first to the remaining ones maintaining some deformation strengthening.) The stress-strain behavior of the samples is compared, conclusions on deformation mechanisms and internal architectures are drawn.

REBCO based coated conductors (CCs) are a viable alternative to conventional superconductors for many applications, therefore the optimization of their current carrying capacity is an ongoing process. A promising route for the increase in performance is the introduction of artificial pinning centers such as BaHfO3 (BHO) nanoparticles. However, granularity still imposes a substantial performance limitation, especially in REBCO CCs deposited on RABiTS based templates, as the critical current density is severely reduced by moderate misalignment angles of adjacent grains. A combined study of scanning Hall probe microscopy and electron microscopy of undoped and BHO-doped YBa2Cu3O7-δ (YBCO) films on technical templates shows that BHO-doping leads to a denser microstructure of the superconducting layer and higher global and local critical current densities. The statistical evaluation of local current maps allows for a quantification of the magnetic granularity where a reduction of granularity with increasing film thickness, doping and increasing temperature is found. In particular, the dependence of granularity on the film thickness and enhanced film growth through BHO-doping shows the potential for further optimization of YBCO films on RABiTS based templates.

To compare the inherent methanol steam reforming properties of intermetallic compounds and a corresponding intermetallic compound–oxide interface, we selected the Cu–In system as a model to correlate the stability limits, self-activation and redox activation properties with the catalytic performance. Three distinct intermetallic Cu–In compounds – Cu7In3, Cu2In and Cu11In9 – were studied both in an untreated and redox-activated state resulting from alternating oxidation–reduction cycles. The stability of all studied intermetallic compounds during methanol steam reforming (MSR) operation is essentially independent of the initial stoichiometry and all accordingly resist substantial structural changes. The inherent activity under batch MSR conditions is highest for Cu2In, corroborating the results of a Cu2In/In2O3 sample accessed through reactive metal–support interaction. Under flow MSR operation, Cu7In3 displays considerable deactivation, while Cu2In and Cu11In9 feature stable performance at simultaneously high CO2 selectivity. The missing significant self-activation is most evident in the operando thermogravimetric experiments, where no oxidation is detected for any of the intermetallic compounds. In situ X-ray diffraction allowed us to monitor the partial decomposition and redox activation of the Cu–In intermetallic compounds into Cu0.9In0.1/In2O3 (from Cu7In3), Cu7In3/In2O3 (from Cu2In) and Cu7In3/Cu0.9In0.1/In2O3 (from Cu11In9) interfaces with superior MSR performance compared to the untreated samples. Although the catalytic profiles appear surprisingly similar, the latter interface with the highest indium content exhibits the least deactivation, which we explain by formation of stabilizing In2O3 patches under MSR conditions., To compare the properties of intermetallic compounds and intermetallic compound–oxide interfaces, Cu–In was used as a model to correlate stability limits, self-activation and redox activation with the inherent methanol steam reforming performance.

Parastoo Delir Kheyrollahi Nezhad; Maged Behkeet; Nicolas Bonmassar; Lukas Schlicker; Albert Gili; Franz Kamutzki; Andrew Doran; Yuanxu Gao; Marc Heggen; Sabine Schwarz; Johannes Bernardi; Bernhard Klötzer; Aligholi Niaei; Ali Farzi; and Simon Penner “Mechanistic In Situ Insights into the Formation, Structural and Catalytic Aspects of the La2NiO4 Intermediate Phase in the Dry Reforming of Methane over Ni-based Perovskite Catalysts”, Applied Catalysis A, Volume 612, (2021), 117984, https://doi.org/10.1016/j.apcata.2020.117984Abstract:We focus on the stability and bulk/surface structural properties of the Ruddlesden-Popper phase La2NiO4 and their consequences for dry reforming of methane (DRM) activity. Fuelled by the appearance as a crucial intermediate during in situ decomposition of highly DRM-active LaNiO3 perovskite structures, we show that La2NiO4 can be equally in situ decomposed into a Ni/La2O3 phase offering CO2 capture and release necessary for DRM activity, albeit at much higher temperatures compared to LaNiO3. Decomposition in hydrogen also leads to an active Ni/La2O3 phase. In situ X-ray diffraction during DRM operation reveals considerable coking and encapsulation of exsolved Ni, yielding much smaller Ni crystallites compared to on LaNiO3, where coking is virtually absent. Generalizing the importance of intermediate Ruddlesden-Popper phases, the in situ decomposition of La-based perovskite structures yields several obstacles due to the high stability of both the parent perovskite and the Ruddlesden-Popper structures and the occurrence of parasitic structures.

Iron-based superconductors are a popular candidate in the search for affordable and simple superconductors for high-field applications. In particular, the relaxed texture requirements fuel hope that films deposited on RABiTS with simple buffer layer architectures could enable cheap coated conductors. We find that a single Yttrium oxide buffer layer can act as a suitable diffusion barrier and epitaxial Fe(Se,Te) thin films were successfully grown by pulsed laser deposition. An analysis of the local current distribution by means of scanning Hall probe microscopy reveals current densities exceeding 1 MA cm−2, however, granularity still seems to be an issue. Transmission electron microscopy images and analysis by transmission Kikuchi diffraction show that the out-of-plane orientation of underlying Ni-W grains in the substrate has a severe impact on the growth of Fe(Se,Te) films.

Nature Communications 12(1), 5046 (2021). doi:10.1038/s41467-021-25320-0, The original version of this Article contained an error in the Acknowledgements section, which was previously incorrectly given as���The authors gratefully acknowledge funding by the Austrian Science Fund (FWF) through project P4509-N16 as well as DESY(Hamburg, Germany), a member of the Helmholtz Association HGF, for the allocation of beamtime and provision of experimentalfacilities.���. The correct version states ���The authors gratefully acknowledge funding by the Austrian Science Fund (FWF) through projectF4509-N16 as well as DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the allocation of beamtime andprovision of experimental facilities.��� in place of the incorrect text. This has been corrected in both the PDF and HTML versions of theArticle., Published by Nature Publishing Group UK, [London]

The influence of A- and/or B-site doping of Ruddlesden–Popper perovskite materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of specific A2BO4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room temperature, B-site doping of La2NiO4 with Cu stabilizes the orthorhombic structure (Fmmm) of the perovskite, while A-site doping with Ba yields a tetragonal space group (I4/mmm). We observed the orthorhombic-to-tetragonal transformation above 170 °C for La2Ni0.9Cu0.1O4 and La2Ni0.8Cu0.2O4, slightly higher than for undoped La2NiO4. Loss of oxygen in interstitial sites of the tetragonal structure causes further structure transformations for all samples before decomposition in the temperature range of 400 °C–600 °C. Controlled in situ decomposition of the parent or A/B-site doped perovskite structures in a DRM mixture (CH4:CO2 = 1:1) in all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in contact with hexagonal La2O3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La2O2CO3, BaCO3). Differences in the catalytic activity evolve because of (i) the in situ formation of Ni–Cu alloy phases (in a composition of >7:1 = Ni:Cu) for La2Ni0.9Cu0.1O4, La2Ni0.8Cu0.2O4, and La1.8Ba0.2Ni0.9Cu0.1O4, (ii) the resulting Ni particle size and amount of exsolved Ni, and (iii) the inherently different reactivity of the present (oxy)carbonate species. Based on the onset temperature of catalytic DRM activity, the latter decreases in the order of La2Ni0.9Cu0.1O4 ∼ La2Ni0.8Cu0.2O4 ≥ La1.8Ba0.2Ni0.9Cu0.1O4 > La2NiO4 > La1.8Ba0.2NiO4. Simple A-site doped La1.8Ba0.2NiO4 is essentially DRM inactive. The Ni particle size can be efficiently influenced by introducing Ba into the A site of the respective Ruddlesden–Popper structures, allowing us to control the Ni particle size between 10 nm and 30 nm both for simple B-site and A-site doped structures. Hence, it is possible to steer both the extent of the metal-oxide-(oxy)carbonate interface and its chemical composition and reactivity. Counteracting the limitation of the larger Ni particle size, the activity can, however, be improved by additional Cu-doping on the B-site, enhancing the carbon reactivity. Exemplified for the La2NiO4 based systems, we show how the delicate antagonistic balance of doping with Cu (rendering the La2NiO4 structure less stable and suppressing coking by efficiently removing surface carbon) and Ba (rendering the La2NiO4 structure more stable and forming unreactive surface or interfacial carbonates) can be used to tailor prospective DRM-active catalysts.

The present paper describes the improvement of the performances of boron powder obtained applying the freeze-drying process (FDP) for the nanostructuration and doping of B2O3, which is here used as boron precursor. After the nanostructuration process, B2O3 is reduced to elemental nanoboron (nB) through magnesiothermic reaction with Mg. For this work, the usefulness of the process was tested focusing on the carbon-doping (C-doping), using Cblack, inulin and haemoglobin as C sources. The choice of these molecules, their concentration, size and shape, aims at producing improvements in the final compound of boron: in this case the superconductive magnesium diboride, which has been prepared and characterized both as powder and wire. The characteristics of B2O3, B and MgB2 powder, as well as MgB2 wire were tested and compared with that obtained using the best commercial precursors: H. C. Starck micrometric boron and Pavezyum nanometric boron. Both the FDP and the magnesiothermic reaction were carried out with simplicity and a great variety of doping sources, i.e. elements or compounds, which can be organic or inorganic and soluble or insoluble. The FDP allows to produce nB suitable for numerous applications. This process is also very competitive in terms of scalability and production costs if compared to the via gas technique adopted by nanoboron producers currently available on the world market.

We present a combined experimental and computational investigation of phase stability and mechanical properties in the Al-Cu-Mg-Zn quaternary system. Samples containing different relative compositions were prepared using magnetron sputtering and investigated by electron microscopic and X-ray based methods. To classify the technical relevance of the samples, the indentation hardness was measured. The phase stability was studied computationally using a cluster expansion approach based on density functional theory (DFT) methods in a comprehensive screening of the structural and stoichiometric configuration space. Upon decreasing Cu concentration, a transition from an FCC to a mixed FCC/BCC crystal system and significant changes in the mechanical properties depending on Valence Electron Concentration (VEC) and atomic size differences ( δ r ) was observed experimentally. The corresponding crystallographic phases were assigned by XRD and the experimentally observed phase transition was confirmed by the computational screening of formation energies. Since to date, quaternary complex light metal alloy systems cannot be reliably predicted, this is an important step towards a priori modelling of this class of materials.

Well-ordered thin films of different defect fluorite and perovskite materials, namely lanthanum zirconate (La2Zr2O7), cerium zirconate (Ce2Zr2O7), lanthanum cerate (La2Ce2O7) and lanthanum strontium ferrite (La0.4Sr0.6FeO3), have been prepared by sputtering the respective powder targets onto vacuum-cleaved NaCl(0 0 1) single crystal facets. Characterization specifically also includes the sophisticated preparation of the initial target materials. For the defect fluorite materials, the target materials are the respective pyrochlore compounds, which reproducibly transform to the respective defect fluorite structures upon sputtering. At template temperatures of around 573 K, well-crystallized epitaxial thin films of the defect fluorite compounds La2Zr2O7 and Ce2Zr2O7 result, whereas for the perovskite compound post-annealing procedures at 973 K in air are necessary to obtain epitaxial ordering of orthorhombic structures. Epitaxial relations for the well-ordered defect fluorite thin films are determined to be La2Zr2O7(0 0 1)//NaCl(0 0 1) and Ce2Zr2O7(0 0 1)//NaCl(0 0 1), respectively. Structural and spectroscopic characterization of the films by (high-resolution) electron microscopy (HR-TEM), selected-area electron diffraction (SAED) and depth-profiling X-ray photoelectron spectroscopy (XPS) reveal that the structures and compositions of the initial target materials are well-preserved during the sputtering process. Following this preparation routine, access to well-ordered thin films of complex oxide materials with defined stoichiometry is therefore granted, which can subsequently be used as model systems for studies of their material’s or catalytic properties, as presented for simpler systems earlier. As a primary example, we show that for the defect fluorite thin films of Ce2Zr2O7 the defect fluorite-pyrochlore phase transformation can be observed at around 1123 K as detected by in situ electron diffraction.

Mg2Si is apart from its conductivity properties expected to be a promising candidate for thermoelectric applications due to its low toxicity, low costs, and the high abundance of its precursor chemicals. Through the addition of a homogeneous distribution of nanoparticles (e.g. MgO) and by reducing the size of Mg2Si to the nanometer regime, it is possible to decrease the thermal conductivity by increasing phonon-interface scattering and, as a result, improve the thermoelectric properties. However, classical approaches do not allow for the synthesis of nanocomposites from Mg2Si and MgO. In this work, a straightforward route is presented towards homogeneously mixed Mg2Si/MgO via a two-step magnesiothermic reduction process starting from sol–gel derived hierarchically organized porous silica. Monolithic materials composed of Mg2Si and MgO in variable molar ratios are built up from a macroporous network of Mg2Si with homogeneously distributed MgO particles exhibiting a crystallite size in the range of 24–37 nm.

A key question in the field of ceramics and catalysis is how and to what extent residual water in the reactive environment of a metal oxide particle powder affects particle coarsening and morphology. With X‐ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), we investigated annealing‐induced morphology changes on powders of MgO nanocubes in different gaseous H2O environments. The use of such a model system for particle powders enabled us to describe how adsorbed water that originates from short exposure to air determines the evolution of MgO grain size, morphology, and microstructure. While cubic nanoparticles with a predominant abundance of (100) surface planes retain their shape after annealing to T = 1173 K under continuous pumping with a base pressure of water p(H2O) = 10−5 mbar, higher water partial pressures promote mass transport on the surfaces and across interfaces of such particle systems. This leads to substantial growth and intergrowth of particles and simultaneously favors the formation of step edges and shallow protrusions on terraces. The mass transfer is promoted by thin films of water providing a two‐dimensional solvent for Mg2+ ion hydration. In addition, we obtained direct evidence for hydroxylation‐induced stabilization of (110) faces and step edges of the grain surfaces.

Bone is a biological tissue with unique mechanical properties, owing to a complex hierarchical structure ranging from the nanoscale up to the macroscale. To better understand bone mechanics, investigation of mechanical properties of all structural elements at every hierarchical level and how they interact is necessary. Testing of bone structures at the lower microscale, e.g. bone lamellae, has been least performed and remains a challenge. Focused ion beam (FIB) milling is an attractive technique for machining microscopic samples from bone material and performing mechanical testing at the microscale using atomic force microscopy (AFM) and nanoindentation setups. So far, reported studies at this length scale have been performed on bone samples of animal origin, mostly in a dehydrated state, except for one study. Here we present an AFM-based microbeam bending method for performing bending measurements in both dehydrated and rehydrated conditions at the microscale. Single lamella bone microbeams of four human donors, aged 65–94 yrs, were machined via FIB and tested both in air and fully submerged in Hank's Balanced Salt Solution (HBSS) to investigate the effect of (de)hydration and to a certain extent, of age, on bone mechanics. Bending moduli were found to reduce up to 5 times after 2 h of rehydration and no trend of change in bending moduli with respect to age could be observed. Mechanical behavior changed from almost purely elastic to viscoelastic upon rehydration and a trend of lower dissipated energy in samples from older donors could be observed in the rehydrated state. These results confirm directly the importance of water for the mechanical properties of bone tissue at the microscale. Moreover, the trend of lowered capability of energy dissipation in older donors may contribute to a decrease of fracture toughness and thus an increase in bone fragility with age.

The present work shows a novel method for generating in-situ low friction tribofilms containing tungsten disulphide in lubricated contacts using diallyl disulphide as sulphur precursor. The approach relies on the tribo-chemical interaction between the diallyl disulphide and a surface containing embedded sub-micrometer tungsten carbide particles. The results show that upon sliding contact between diallyl disulphide and the tungsten-containing surface, the coefficient of friction drops to values below 0.05 after an induction period. The reason for the reduction in friction is due to tribo-chemical reactions that leads to the in-situ formation of a complex tribofilm that contains iron and tungsten components. X-ray photoelectron spectroscopy analyses indicate the presence of tungsten disulphide at the contact interface, thus justifying the low coefficient of friction achieved during the sliding experiments. It was proven that the low friction tribofilms can only be formed by the coexistence of tungsten and sulphur species, thus highlighting the synergy between diallyl disulphide and the tungsten-containing surface. The concept of functionalizing surfaces to react with specific additives opens up a wide range of possibilities, which allows tuning on-site surfaces to target additive interactions.

Ge1–xSnx nanorods (NRs) with a nominal Sn content of 28% have been prepared by a modified microwave-based approach at very low temperature (140 °C) with Sn as growth promoter. The observation of a Sn-enriched region at the nucleation site of NRs and the presence of the low-temperature α-Sn phase even at elevated temperatures support a template-assisted formation mechanism. The behavior of two distinct Ge1–xSnx compositions with a high Sn content of 17% and 28% upon thermal treatment has been studied and reveals segregation events occurring at elevated temperatures, but also demonstrates the temperature window of thermal stability. In situ transmission electron microscopy investigations revealed a diffusion of metallic Sn clusters through the Ge1–xSnx NRs at temperatures where the material composition changes drastically. These results are important for the explanation of distinct composition changes in Ge1–xSnx and the observation of solid diffusion combined with dissolution and redeposition of Ge1–ySny (...