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The structure of the first lithium containing bismuth ortho-thiophosphate was solved using a combination of powder X-ray, neutron, and electron diffraction. Li60–3xBi16+x(PS4)36 with x in the range of 4.2 to 6.7 possesses a complex monoclinic structure (space group C2/c, no. 15) and a large unit cell with lattice parameters a = 15.487Å, b = 10.323Å, c = 33.767Å, and = 85.394° for Li44.4Bi21.2(PS4)36. The disordered distribution of lithium ions within the interstices of the dense host-structure as well as the Li ion dynamics and diffusion pathways have been investigated by X-ray and neutron PDF analysis, solid-state NMR spectroscopy, PFG-NMR diffusion measurements, and BVS calculations. The total lithium ion conductivities range from 2.6 × 10−7 to 2.8 × 10−6 S cm−1 at 20 °C with activation energies between 0.29 and 0.32 eV, depending on the bismuth content. Despite the highly disordered nature of lithium ions in Li60–3xBi16+x(PS4)36, the underlying dense host-framework appears to limit the dimensionality of the lithium diffusion pathways and emphasizes once more the necessity of a close inspection of structure-property relationships in solid electrolytes.

The prevalent global energy crisis calls for searching viable pathways for generating green hydrogen as an alternative energy resource. Dye-sensitized photocatalytic water splitting is a feasible solution to produce green hydrogen. However, identifying suitable catalysts has been one of the bottlenecks in driving dye-sensitized photocatalysis efficiently. In this work, we report a new class of electrocatalysts based on the layered Weyl semimetals MIrTe4 (M = Nb, Ta) for the Eosin Y (EY)-sensitized hydrogen evolution reaction (HER) under visible light illumination. NbIrTe4 and TaIrTe4 exhibit HER activities of ~ 18000 and ~ 14000 mol.g-1, respectively after 10h of irradiation with visible light. Time-dependent UV-Vis spectroscopy and high-pressure liquid chromatography coupled with mass spectroscopy analysis shed light on the reaction dynamics and enable deeper understanding of the observed trend in hydrogen evolution rates for MIrTe4 materials. MIrTe4 (M = Nb, Ta) semimetals outperform related catalysts including transition metal dichalcogenides and other Weyl semimetals in terms of HER activity using EY as photosensitizer and triethanolamine as the sacrificial agent. We hypothesize that the topology-related band inversion in MIrTe4 Weyl semimetals promotes a high density of metal d-states near the Fermi level, driving their high catalytic performance. This study introduces a new class of layered Weyl semimetals as efficient catalysts, and provides perspectives for designing topology-enhanced catalysts.

Directed design of new photocatalysts remains a challenging task in materials chemistry. One approach in metal oxides is to engineer the bulk electronic structure to achieve enhanced visible-light ...

The development of all-solid-state sodium batteries for scalable energy storage solutions requires fast sodium conducting solid electrolytes. To fast-track their discovery, candidate materials need to be identified that are synthesized from abundant resources via cheap and green synthesis routes. Their ion conducting mechanism has to be understood and adapted to meet the stringent requirements for long-term operation in all-solid-state batteries. Here, structure and properties of the sodium hexathiohypodiphosphate Na4P2S6 obtained by two different synthesis methods are compared: a solid-state reaction and a precipitation route from aqueous solution. Combined investigations using powder X-ray diffraction (PXRD), precession electron diffraction (PED), differential scanning calorimetry (DSC), solid-state nuclear magnetic resonance spectroscopy (ssNMR), and Raman spectroscopy reveal that the solid-state synthesized material is characterized by a Na+ and vacancy disorder-driven enantiotropic phase transition at 160 °C (α- to β-Na4P2S6), which is accompanied by a symmetry change of the P2S64− anion. Precipitated Na4P2S6 already crystallizes in a β-like polymorph at room temperature, likely assisted by inter- and intralayer defects. Bond-valence and nudged elastic band (NEB) calculations were employed to identify a low energy, 2D conduction network in β-Na4P2S6, suggesting facile 2D long-range Na+ diffusion. Electrochemical impedance spectroscopy reveals a higher ionic conductivity at room temperature in precipitated β-like Na4P2S6 (2 × 10−6 S cm−1) compared to the solid-state α polymorph (7 × 10−7 S cm−1). The activation energy is around 0.4 eV for both materials. The findings highlight that even subtle structural changes can significantly impact the sodium-ion diffusion in solid electrolytes and at the same time reveal an intricate interplay between phase formation and synthetic control.

In this study, a strategy to prepare CuO/Cu2O/Cu microwires that are fully covered by a nanowire (NW) network using a simple thermal-oxidation process is developed. The CuO/Cu2O/Cu microwires are fixed on Au/Cr pads with Cu microparticles. After thermal annealing at 425 °C, these CuO/Cu2O/Cu microwires are used as room-temperature 2-propanol sensors. These sensors show different dominating gas responses with operating temperatures, e.g., higher sensitivity to ethanol at 175 °C, higher sensitivity to 2-propanol at room temperature and 225 °C, and higher sensitivity to hydrogen gas at ∼300 °C. In this context, we propose the sensing mechanism of this three-in-one sensor based on CuO/Cu2O/Cu. X-ray diffraction (XRD) studies reveal that the annealing time during oxidation affects the chemical appearance of the sensor, while the intensity of reflections proves that for samples oxidized at 425 °C for 1 h the dominating phase is Cu2O, whereas upon further increasing the annealing duration up to 5 h, the CuO phase becomes dominant. The crystal structures of the Cu2O-shell/Cu-core and the CuO NW networks on the surface were confirmed with a transmission electron microscope (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED), where (HR)TEM micrographs reveal the monoclinic CuO phase. Density functional theory (DFT) calculations bring valuable inputs to the interactions of the different gas molecules with the most stable top surface of CuO, revealing strong binding, electronic band-gap changes, and charge transfer due to the gas molecule interactions with the top surface. This research shows the importance of the nonplanar CuO/Cu2O layered heterostructure as a bright nanomaterial for the detection of various gases, controlled by the working temperature, and the insight presented here will be of significant value in the fabrication of new p-type sensing devices through simple nanotechnology.

Carbon nitrides are among the most studied materials for photocatalysis, however, limitations arise from inefficient charge separation and transport within the material. Here, this aspect is addressed in the 2D carbon nitride poly(heptazine imide) (PHI) by investigating the influence of various counterions, such as M = Li+, Na+, K+, Cs+, Ba2+, NH4+ and tetramethyl ammonium, on the material’s conductivity and photocatalytic activity. These ions in the PHI pores affect the stacking of the 2D layers, which further influences the predominantly ionic conductivity in M-PHI. Na-containing PHI outperforms the other M-PHI in various relative humidity (RH) environments (0-42 %RH) in terms of conductivity, likely due to pore channel geometry and size of the (hydrated) ion. With increasing RH, the ionic conductivity increases by 4-5 orders of magnitude (for Na-PHI up to 10-5 S cm-1 at 42 %RH). At the same time, the highest photocatalytic hydrogen evolution rate is observed for Na-PHI, which is mirrored by increased photo-generated charge carrier lifetimes, pointing to efficient charge carrier stabilization by mobile ions. These results indicate that ionic conductivity is an important parameter that can influence the photocatalytic activity. Besides, RH-dependent ionic conductivity is of high interest for separators, membranes, or sensors.

The in-depth understanding of the reported photoelectrochemical properties of the layered carbon nitride, poly(triazine imide)/LiCl (PTI/LiCl), has been limited by the apparent disorder of the Li/H atoms within its framework. To understand and resolve the current structural ambiguities, an optimized one-step flux synthesis (470 oC, 36 h, LiCl/KCl flux) was used to prepare PTI/LiCl and deuterated-PTI/LiCl in high purity. Its structure was characterized by a combination of neutron/X-ray diffraction and transmission electron microscopy. The range of possible Li/H atomic configurations were enumerated for the first time and, combined with total energy calculations, reveals a more complex energetic landscape than previously considered. Experimental data were fitted against all possible structural models, exhibiting the most consistency with a new orthorhombic model (Sp. Grp. Ama2) that also has the lowest total energy. In addition, a new Cu(I)-containing PTI (PTI/CuCl) was prepared with the more strongly scattering Cu(I) cations in place of Li, and which also most closely matched with the partially-disorded structure in Cmc21. Thus, a complex configurational landscape of PTI is revealed to consist of a number of ordered crystalline structures that are new potential synthetic targets, such as with the use of metal-exchange reactions.

The rational design of catalysts is crucial to make power-to-X technologies viable. Here the authors introduce the delafossite PdCoO2 as a highly active hydrogen evolution reaction catalyst due to the growth of a tensile-strained Pd-rich capping layer under reductive conditions. Image credit: Christop Hohmann., The rational design of hydrogen evolution reaction electrocatalysts that can compete with platinum is an outstanding challenge in the process of designing viable power-to-gas technologies. Here, we introduce delafossites as a family of hydrogen evolution reaction electrocatalysts in acidic media. We show that, in PdCoO2, the inherently strained Pd metal sublattice acts as a pseudomorphic template for the growth of a tensile-strained Pd-rich capping layer under reductive conditions. The surface modification ranges up to 400 nm and continuously improves the electrocatalytic activity by simultaneously increasing the exchange current density and by reducing the Tafel slope down to 38 mV dec(-1), leading to overpotentials eta(10) < 15 mV. The improved activity is attributed to the operando stabilization of a beta-PdHx phase with enhanced surface catalytic properties with respect to pure or nanostructured palladium. These findings illustrate how operando-induced electrodissolution can be used as a top-down design concept through the strain-stabilized formation of catalytically active phases.

A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2 Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59-25 μm is also significantly wider than that of AGS (ca. 0.48-≈11.4 μm). The occurrence of the strong SHG responses and good phase-matching indicate that the structure of the new Ga2 Se3 phase can only be non-centrosymmetric and have a lower symmetry than the cubic γ-phase. The observed excellent SHG and phase-matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

The carbon nitride poly(heptazine imide), PHI, has recently emerged as a powerful 2D carbon nitride photocatalyst with intriguing charge storing ability. Yet, insights into how morphology, particle size and defects influence its photophysical properties are virtually absent. Here, ultrasonication is used to systematically tune the particle size as well as concentration of surface functional groups and study their impact. Enhanced photocatalytic activity correlates with an optimal amount of those defects that create shallow trap states in the optical band gap, promoting charge percolation, as evidenced by time-resolved photoluminescence spectroscopy, charge transport studies, and quantum-chemical calculations. Excessive amounts of terminal defects can act as recombination centers and hence, decrease the photocatalytic activity for hydrogen evolution. Re-agglomeration of small particles can, however, partially restore the photocatalytic activity. The type and amount of trap states at the surface can also influence the deposition of the co-catalyst Pt, which is used in hydrogen evolution experiments. Optimized conditions entail improved Pt distribution, as well as an enhanced wettability and colloidal stability. A description of the interplay between these effects is provided to obtain a holistic picture of the size–property–activity relationship in nanoparticulate PHI-type carbon nitrides that can likely be generalized to related photocatalytic systems.

Covalent organic frameworks have emerged as a powerful synthetic platform for installing and interconverting dedicated molecular functions on a crystalline polymeric backbone with atomic precision. Here, we present a novel strategy to directly access amine-linked covalent organic frameworks, which serve as a scaffold enabling pore-wall modification and linkage-interconversion by new synthetic methods based on Leuckart-Wallach reduction with formic acid and ammonium formate. Frameworks connected entirely by secondary amine linkages, mixed amine/imine bonds, and partially formylated amine linkages are obtained in a single step from imine-linked frameworks, or directly from corresponding linkers in a one-pot crystallisation-reduction approach. The new, 2D amine-linked covalent organic frameworks, rPI-3-COF, rTTI-COF, and rPy1P-COF, are obtained with high crystallinity and large surface areas. Secondary amines, installed as reactive-sites on the pore wall, enable further post-synthetic functionalisation to access tailored covalent organic frameworks, with increased hydrolytic stability, as potential heterogeneous catalysts.

In this study, a strategy to prepare CuO/Cu

Powder samples of Ag3LiIr2O6 and Ag3LiRu2O6 were synthesized from alpha-Li2IrO3 and Li2RuO3 respectively by ion exchange in an AgNO3 melt. The crystal structures of the title compounds were solved from high resolution laboratory X-ray powder diffraction (XRPD) patterns and from pair distribution function (PDF) analysis using synchrotron X-ray powder diffraction data. In both crystal structures edge sharing LiO6/3- and (Ir/Ru)O-6/3-octahedra form honeycomb like layers that are stacked in a staggered fashion. Silver cations, situated in-between the layers mediate the interlayer interactions by linear O-Ag-O bonds. Anisotropic peak broadening in the XRPD patterns and diffuse scattering occurring as streaks in the precession electron diffraction (PED) patterns indicate the presence of stacking faults, which could be also visualized by high resolution transmission electron microscopy (HRTEM). Possible alternative stacking sequences were derived from the ideal crystal and incorporated into a microstructure model. By applying a supercell approach that randomly generates and averages stacking sequences based on transition probabilities and combining it with a grid search algorithm, the microstructures, i.e. the degrees of faulting in the structures of the title compounds were refined to the measured XRPD data. In result the crystal structures of Ag3LiIr2O6 and Ag3LiRu2O6 were found to be vastly faulted with almost no coherence of the stacked layers.

The occurrence of a unique 3D nanoscale network in Ni–Cr–S, treated via spark-plasma sintering, was discovered with a variety of ex situ and in situ TEM and XRD techniques. The starting material, consisting of a heterogeneous mixture of different phases, could be purified upon application of the sintering process. The obtained samples showed a network of chemically segregated domains being either Ni rich and Cr deficient or vice versa. These domains could be proven to intergrow fully coherently in 3D, thus establishing a unique microstructure. Electron beam irradiation caused the initial Cr3S4-type structures to transform into the disordered NiAs-type. The disordering is characterised by significant short-range ordering as indicated by the appearance of prominent diffuse scattering. Thermoelectric characterisation at room temperature indicated an n-type semiconductor behaviour with thermal and electrical conductivities similar to usual thermoelectric materials, however with a low Seebeck coefficient and a low power factor of 49.3 μW m−1 K−2.

Tuning the chemical composition and structure for targeted functionality in two-dimensional (2D) nanosheets has become a major objective in the rapidly growing area of 2D materials. In the context of photocatalysis, both miniaturization and extending the light absorption of UV active photocatalysts are major assets. Here, we investigate the solid solution between two photocatalytic systems known from literature to evolve H-2 from water/methanol under UV-RbCa2Nb3O10 (E-g = 3.7 eV) -and visible light irradiation - RbPb2Nb3O10 (E-g = 3.0 eV) - by synthesizing hypothetical RbCa2-xPbxNb3O10. While the calcium niobate can easily be exfoliated into individual nanosheets via cation-proton exchange and subsequent treatment with tetra-n-butyl-ammonium hydroxide (TBAOH), the lead niobate barely yields nano-sheets. Spectroscopic and microscopic analysis suggest that this is caused by volatilization of Pb during synthesis, leading to a local 3D linkage of RbPb2Nb3O10 perovskite units with Pb deficient units. On the one hand, this linkage progressively prevents exfoliation along with an increasing Pb content. On the other hand, introducing Pb into the perovskite blocks successively leads to bandgap narrowing, thus gradually enhancing the light harvesting capability of the solid solution. Finding a compromise between this narrowing of the bandgap and the possibility of exfoliation, visible light sensitized nanosheets can be engineered in good yield for an initial molar ratio of Ca:Pb >= 1:1.

Novel anodes for Li-ion batteries have been characterized by transmission electron microscopy (TEM). The anodes consist of arrays of ordered silicon microwires obtained from conventional silicon wafers by controlled etching processes. Suitable preparation methods for wires in the micrometer range have been tested, optimized, and subsequently applied. Ex situ TEM measurements have been performed for pristine as well as for electrochemically cycled wires that have been charged and discharged for several times. The influences of cycling rate, an electrolyte additive, as well as elevated temperatures on the anodes’ stability have been investigated.

The discovery of 2D forms of matter, pioneered by graphene, has not only triggered new insights into fundamental physics but also pushed the limits of miniaturization. To process nanosheets into ultrathin functional devices, the development of scalable exfoliation routes is of key interest. Here, we demonstrate for the first time a mild, yet highly effective silver-ion-based exfoliation route for layered transition metal oxides. Single layer transition metal oxide nanosheets were obtained by applying silver ion exchange and subsequent treatment of the silver-intercalated phases with an aqueous suspension containing organic iodides. This generic exfoliation route can be widely applied also to acid-sensitive materials and allows the modification of the nanosheets with non-conventional organic ligands, which owing to their chemical functionality may be used to tailor the optoelectronic and surface properties of the nanosheet–ligand hybrid.

3D networks of Al-doped ZnO tetrapods decorated with ZnAl

Powder samples of Ag3LiIr2O6 and Ag3LiRu2O6 were synthesized from α-Li2IrO3 and Li2RuO3 respectively by ion exchange in an AgNO3 melt. The crystal structures of the title compounds were solved from high resolution laboratory X-ray powder diffraction (XRPD) patterns and from pair distribution function (PDF) analysis using synchrotron X-ray powder diffraction data. In both crystal structures edge sharing LiO6/3- and (Ir/Ru)O6/3-octahedra form honeycomb like layers that are stacked in a staggered fashion. Silver cations, situated in-between the layers mediate the interlayer interactions by linear O-Ag-O bonds. Anisotropic peak broadening in the XRPD patterns and diffuse scattering occurring as streaks in the precession electron diffraction (PED) patterns indicate the presence of stacking faults, which could be also visualized by high resolution transmission electron microscopy (HRTEM). Possible alternative stacking sequences were derived from the ideal crystal and incorporated into a microstructure model. By applying a supercell approach that randomly generates and averages stacking sequences based on transition probabilities and combining it with a grid search algorithm, the microstructures, i.e. the degrees of faulting in the structures of the title compounds were refined to the measured XRPD data. In result the crystal structures of Ag3LiIr2O6 and Ag3LiRu2O6 were found to be vastly faulted with almost no coherence of the stacked layers.

The single-step incorporation of multiple immiscible elements into colloidal high-entropy alloy (HEA) nanoparticles has manifold technological potential, but it continues to be a challenge for state-of-the-art synthesis methods. Hence, the development of a synthesis approach by which the chemical composition and phase of colloidal HEA nanoparticles can be controlled could lead to a new pool of nanoalloys with unparalleled functionalities. Herein, this study reports the single-step synthesis of colloidal CoCrFeMnNi HEA nanoparticles with targeted equimolar stoichiometry and diameters less than 5 nm by liquid-phase, ultrashort-pulsed laser ablation of the consolidated and heat-treated micropowders of the five constituent metals. Further, the scalability of the process with an unprecedented productivity of 3 grams of colloidal HEA nanoparticles per hour is demonstrated. Electrochemical analysis reveals a unique redox behavior of the particles' surfaces in an alkaline environment and a potential for future application as a heterogeneous catalyst for the oxygen evolution reaction.

Joints of three-dimensional (3D) rutile-type (r) tin dioxide (SnO2) nanowire networks, produced by the flame transport synthesis (FTS), are formed by coherent twin boundaries at (101)r serving for the interpenetration of the nanowires. Transmission electron microscopy (TEM) methods, i.e. high resolution and (precession) electron diffraction (PED), were utilized to collect information of the atomic interface structure along the edge-on zone axes [010]r, [111]r and superposition directions [001]r, [101]r. A model of the twin boundary is generated by a supercell approach, serving as base for simulations of all given real and reciprocal space data as for the elaboration of three-dimensional, i.e. relrod and higher order Laue zones (HOLZ), contributions to the intensity distribution of PED patterns. Confirmed by the comparison of simulated and experimental findings, details of the structural distortion at the twin boundary can be demonstrated.

We report on the structural alterations of the thermoelectric material CuCrS2 introduced by the removal of 1/3 of the Cu+ ions which are located between CrS2 layers. X-ray diffraction (XRD) and pair distribution function (PDF) analyses revealed a newly formed Cu0.66CrS2 phase with monoclinic symmetry and a 3a superstructure. Simultaneously, a distortion of CrS6 octahedra is observed strongly indicating the oxidation of Cr3+ → Cr4+ leading to a Jahn–Teller distortion. The structural features extracted from XRD indicate a pronounced disorder in the cationic sub-lattice at moderate temperatures (400 K). Transmission electron microscopy (TEM) examination elucidates the formation of a second Cu0.66CrS2 phase without the superstructure, caused by incipient Cu+ mobility upon beam irradiation. The synergetic combination of high temperature XRD and TEM investigations unveiled the complete mechanism of the phase transition occurring at 503 K, where a transformation into the spinel CuCr2S4 and stoichiometric CuCrS2 occurs.

Five new compounds in the Cu/P/Se phase diagram have been synthesized, and their crystal structures have been determined. The crystal structures of these compounds comprise four previously unreported zero-, one-, and two-dimensional selenidophosphate anions containing low-valent phosphorus. In addition to two new modifications of Cu4P2Se6 featuring the well-known hexaselenidohypodiphosphate(IV) ion, there are three copper selenidophosphates with low-valent P: Cu4P3Se4 contains two different new anions, (i) a monomeric (zero-dimensional) selenidophosphate anion [P2Se4](4-) and (ii) a one-dimensional selenidophosphate anion [Formula: see text], which is related to the well-known gray-Se-like [Formula: see text] Zintl anion. Cu4P4Se3 contains one-dimensional [Formula: see text] polyanions, whereas CuP2Se contains the 2D selenidophosphate [Formula: see text] polyanion. It consists of charge-neutral CuP2Se layers separated by a van der Waals gap which is very rare for a Zintl-type phase. Hence, besides black P, CuP2Se constitutes a new possible source of 2D oxidized phosphorus containing layers for intercalation or exfoliation experiments. Additionally, the electronic structures and some fundamental physical properties of the new compounds are reported. All compounds are semiconducting with indirect band gaps of the orders of around 1 eV. The phases reported here add to the structural diversity of chalcogenido phosphates. The structural variety of this family of compounds may translate into a variety of tunable physical properties.

Titanium-rich TiNiCu shape memory thin films with ultralow fatigue have been analysed for their structural features by transmission electron microscopy. The stabilization of austenite (B2) and orthorhombic martensite (B19) variants epitaxially connected to Ti2Cu-type precipitates has been observed and found responsible for the supreme mechanical cycling capability of these compounds. Comprehensiveex situandin situcooling/heating experiments have demonstrated the presence of an austenitic nanoscale region in between B19 and Ti2Cu, in which the structure shows a gradual transition from B19 to B2 which is then coupled to the Ti2Cu precipitate. It is proposed that this residual and epitaxial austenite acts as a template for the temperature-induced B2↔B19 phase transition and is also responsible for the high repeatability of the stress-induced transformation. This scenario poses an antithesis to residual martensite found in common high-fatigue shape memory alloys.

Joints of three-dimensional (3D) rutile-type (r) tin dioxide (SnO2) nanowire networks, produced by the flame transport synthesis (FTS), are formed by coherent twin boundaries at (101)r serving for the interpenetration of the nanowires. Transmission electron microscopy (TEM) methods, i.e. high resolution and (precession) electron diffraction (PED), were utilized to collect information of the atomic interface structure along the edge-on zone axes [010]r, [111]r and superposition directions [001]r, [101]r. A model of the twin boundary is generated by a supercell approach, serving as base for simulations of all given real and reciprocal space data as for the elaboration of three-dimensional, i.e. relrod and higher order Laue zones (HOLZ), contributions to the intensity distribution of PED patterns. Confirmed by the comparison of simulated and experimental findings, details of the structural distortion at the twin boundary can be demonstrated.

In this work, a facile two-step fabrication and characterization of printed acetone sensors based on mixed semiconducting metal oxides is introduced. The devices are fabricated by Direct Ink Writing metal microparticle (MP) stripes of commercially available pure iron and copper particles onto the surface of a glass substrate, forming a bridging multi-phase semiconducting oxide net by subsequent thermal annealing. The open, highly porous bridging structures consist of heterojunctions which are interconnected via non-planar CuO/Cu2O/Cu nanowires and Fe2O3/Fe nanospikes. Morphological, vibrational, chemical and structural studies were performed to investigate the contact-forming Fe2O3–CuO nanostructures on the surface of the MPs. The power consumption and the gas sensing properties showed selectivity to acetone vapor at an operating temperature of around 300 °C with a high gas response of about 50% and the lowest operating power of around 0.26 μW to a concentration of 100 ppm of acetone vapor. The combination of the possibility of acetone vapor detection, the controllable size and geometry and their low power make these printed structures important candidates for next developments of accessible detection devices, as well as acetone vapor monitoring (even below 1 ppm). The printing of MPs in general paves the way for a new generation of printed different devices, even in “home-made” conditions, for a manifold of applications tailored by the composition and geometry of the printed MP stripes, enabled through the simplicity and versatility of the fabrication method.

Stabilization of covalent organic frameworks (COFs) by post-synthetic locking strategies is a powerful tool to push the limits of COF utilization, which are imposed by the reversible COF linkage. Here we introduce a sulfur-assisted chemical conversion of a two-dimensional imine-linked COF into a thiazole-linked COF, with full retention of crystallinity and porosity. This post-synthetic modification entails significantly enhanced chemical and electron beam stability, enabling investigation of the real framework structure at a high level of detail. An in-depth study by electron diffraction and transmission electron microscopy reveals a myriad of previously unknown or unverified structural features such as grain boundaries and edge dislocations, which are likely generic to the in-plane structure of 2D COFs. The visualization of such real structural features is key to understand, design and control structure–property relationships in COFs, which can have major implications for adsorption, catalytic, and transport properties of such crystalline porous polymers., Stabilization of covalent organic frameworks (COFs) by post-synthetic locking is a powerful tool to push the limits of COF utilization. Here the authors demonstrate a sulfur-assisted conversion of an imine-linked COF into a thiazole-linked COF, with retention of crystallinity and porosity, allowing for direct imaging of defects in COFs.

Development of high-performance p-type semiconductor based gas sensors exhibiting fast-response/recovery times with ultra-high response are of major importance for gas sensing applications. Recent reports demonstrated the excellent properties of p-type semiconducting oxide for various practical applications, especially for selective oxidation of volatile organic compounds (VOCs). In this work, sensors based on CuO nanowire (NW) networks have been successfully fabricated via a simple thermal oxidation process on pre-patterned Au/Cr pads. Our investigation demonstrates high impact of the process temperature on aspect ratio and density of copper oxide NWs. An optimal temperature for growth of thin and densely packed NWs was found to be at 425 degrees C. The fabricated sensors demonstrated ultra-high gas response by a factor of 313 to ethanol vapour (100 ppm) at an operating temperature of 250 degrees C. High stability and repeatability of these sensors indicate the efficiency of p-type oxide based gas sensors for selective detection of VOCs. A high-performance nanodevice was fabricated in a FIB-SEM system using a single CuO NW, demonstrating an ethanol response of 202 and rapid response and recovery of similar to 198 ms at room temperature. The involved gas sensing mechanism of CuO NW networks has been described. We consider that the presented results will be of a great interest for the development of higherperformance p-type semiconductor based sensors and bottomup nanotechnologies. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A 0-3 nanocomposite of CdSe (crystalline nanoparticles) and Cr2Se3 (amorphous matrix) was synthesized via a soft chemical approach and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Particularly the transformation of the 0-3 composite is explored in situ under electron beam irradiation and thermal annealing inside the TEM. In situ electron beam irradiation removed exclusively the CdSe nanoparticles and generated a porous Cr2Se3 matrix with a slightly increased crystallinity. The highly localized beam heating and knock-on effect are attributed to the origin of the in situ irradiation transformation. During the in situ thermal annealing process of the 0-3 nanocomposite CdSe particles are eliminated and crystalline nano-and microparticles of Cr2Se3 are generated. Also the formation of chromium enriched crystallites is observed. All of these in situ results are compared with conventional ex situ methods and discussed in terms of the different mechanisms associated with electron beam interaction and size effects of the nanocomposite.

Here we report for the first time on a complete simulation assisted "material to module" development of a high performance thermoelectric generator (TEG) based on the combination of a phase change material and established thermoelectrics yielding the compositions (1 - x)(GeTe) x(Bi(2)Se(0.2)Te(2.8)). For the generator design our approach for benchmarking thermoelectric materials is demonstrated which is not restricted to the determination of the intrinsically imprecise ZT value but includes the implementation of the material into a TEG. This approach is enabling a much more reliable benchmarking of thermoelectric materials for TEG application. Furthermore we analyzed the microstructure and performance close to in-operandi conditions for two different compositions in order to demonstrate the sensitivity of the material against processing and thermal cycling. For x = 0.038 the microstructure of the as-prepared material remains unchanged, consequently, excellent and stable thermoelectric performance as prerequisites for TEG production was obtained. For x = 0.063 we observed strain phenomena for the pristine state which are released by the formation of planar defects after thermal cycling. Consequently the thermoelectric performance degrades significantly. These findings highlight a complication for deriving the correlation of microstructure and properties of thermoelectric materials in general.

We report the high-pressure synthesis and the structure of aluminum hexathiohypodiphosphate, Al4(P2S6)3, along with the redetermination of the structures of two modifications of AlPS4. Al4(P2S6)3 crystallizes in the monoclinic space group C2 with a = 17.584(3), b = 10.156(2), c = 6.698(1) A, β = 106.93(1)° in a superstructure of the layered FePS3 structure type with tripled a axis. Hereby, Al3+ occupies 2/3 of the Fe2+ sites in an ordered fashion. The structure model obtained from single-crystal X-ray diffraction was corroborated by TEM-PED. The low-temperature modification of AlPS4 with platelet-like morphology shows tetragonal symmetry [space group P2c, a = b = 5.6572(9), c = 9.220(2) A]. The orthorhombic high-temperature modification with fibrous needle-like morphology of AlPS4 is isotpyic with BPS4 [space group I222, a = 5.660(2), b = 5.759(2), c = 9.189(2) A].

The atomic structure of the incommensurate Pd5B1-z phase has been analysed in detail by selected area electron diffraction and neutron-powder diffraction. That structure is based on a close-packed cubic arrangement of Pd atoms with the B atoms occupying the octahedral sites in a long-range ordered fashion. The ordering pattern of B is an incommensurately modulated one with a modulation vector of a length which changes with the B content (~PdB0.18-0.19) to adapt the ordering pattern continuously to the actual composition. The structure can be conceived to be constituted from “isolated” BPd6 units (also occurring in the previously reported Pd6B phase) and edge-sharing B2Pd10 octahedra units, which occur in a ratio reflecting the actual B content. As predicted on the basis of elastic interactions between B atoms, nearest neighbour B-B pairs occur (the B2Pd10 double octahedra units) in the structure of the Pd5B1-z phase, whereas occurrence of second-nearest neighbour B-B pairs is avoided. For the ideal composition Pd5B the crystal structure of the Pd5B1-z phase corresponds to that of monoclinic UCl5 with U playing the role of B and Cl that of Pd.

Ferroelectric lead-free thin films of the composition (Ba0.85Ca0.15)(Ti0.9Zr0.1)O-3 (BCZT) were deposited by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates using a ceramic BCZT target prepared by a conventional solid state reaction. The target material itself shows a piezoelectric coefficient of d(33)=640pm/V. The (111) textured thin films possess a thickness of up to 1.1 mu m and exhibit a clamped piezoelectric response f of up to 190pm/V, a dielectric coefficient of (r)=2000 at room temperature, and a pronounced relaxor behavior. As indicated by transmission electron microscopy, the thin films are composed of longitudinal micrometersized columns with similar to 100nm lateral dimension that are separated at twin- and antiphase boundaries. The superposition phenomena according to this columnar growth were simulated based on suitable supercells. The major structural component is described as a tetragonal distorted variant of the perovskite parent type; however, frequently coherently intergrown nanodomains were observed indicating a much more complex structure that is characterized by a 7-layer modulation along the growth direction of the films.

The fabrication of highly active and robust hexagonal ruthenium oxide nanosheets for the electrocatalytic oxygen evolution reaction (OER) in an acidic environment is reported. The ruthenate nanosheets exhibit the best OER activity of all solution-processed acid medium electrocatalysts reported to date, reaching 10 mA cm(-2) at an overpotential of only approximate to 255 mV. The nanosheets also demonstrate robustness under harsh oxidizing conditions. Theoretical calculations give insights into the OER mechanism and reveal that the edges are the origin of the high OER activity of the nanosheets. Moreover, the post OER analyses indicate, apart from coarsening, no observable change in the morphology of the nanosheets or oxidation states of ruthenium during the electrocatalytic process. Therefore, the present investigation suggests that ruthenate nanosheets are a promising acid medium OER catalyst with application potential in proton exchange membrane electrolyzers and beyond.

International audience; Two-dimensional materials do not only attract interest owing to their anisotropic properties and quantum confinement effects but also lend themselves as well-defined building blocks for the rational design of 3D materials with custom-made structures and, hence, properties. Here, we present the bottom-up fabrication of an artificial superlattice derived from positively charged layered double hydroxide (LDH) and negatively charged perovskite layers sequentially assembled by electrostatic layer-by-layer deposition. In contrast to previously employed bulk methods averaging out the elemental distribution within such stacks, we use a combination of HRTEM, STEM, and EEL spectroscopy to elucidate the structure and composition of the multilayer stack with a high spatial resolution on the subnanometer scale. Atomic column resolved STEM coupled with EELS line scans confirms the periodic arrangement of individual nanosheets by evaluation of the Ca-L2,3 and Mn-L2,3 edges. Furthermore, HRTEM confirms the formation of up to 100 double layer thick films, thus demonstrating the transition from ultrathin nanosheet assemblies to artificial bulk solids with engineered structures and property profiles. We ascertain the formation of densely packed stacks with a well-ordered layered morphology, while nonidealities such as lack of in-plane layer registry, layer terminations, sheet bending, and contamination by residual ligands are side effects of the solution-based deposition process. In addition, we demonstrate that the packing density of the multilayer system can be tuned by changing the LDH dispersing agent from formamide to water, resulting in porous stacks containing about eight times less LDH and featuring significantly increased interlayer distances.

Mineral samples from the Prasolovskoe epithermal Au-Ag deposit, Russia, were investigated via transmission electron microscopy (TEM). One component was identified as the mineral kurilite Ag8Te3Se according to the data obtained from electron diffraction (ED) and Fourier transform analyses of high resolution micrographs. Micrometer-sized grains of kurilite were found next to other noble metal chalcogenide domains like the hessite-type. The EDX microprobe analyses of the kurilite domains were determined with the chemical composition Ag7.9Au0.1Te2.9Se1.0 which is consistent with kurilite doped by gold. Additionally noble metal polychalcogenidehalides (NMPH) were identified via ED. Monoclinic and tetragonal polymorphs of Ag5Te2Cl were observed for the first time in a mineral sample. One additional component, whose composition equates the kurilite-type component with regard to Ag, Au, Te, and Se but with a marginal chlorine component, crystallizes in a structure type known from synthetic NMPH, namely Ag23Te12X (X = Cl, Br). This phase as well as the phases Ag10Te4Br3 and Ag20Te10Br2 was found next to each other in an also investigated synthetic sample.

The morphology and real structure of wurtzite-type ZnO nanospikes grown by the recently introduced flame transport synthesis have been examined by means of advanced transmission electron microscopy (TEM). The rapid synthesis produces nanospikes showing a well defined texture which restricts TEM experiments to a preferred viewing direction of [2 {\overline 1}{\overline 1}3]. Forced by the specific morphology, all of the observed nanospikes show a complicated superposition of twinned domains as an intrinsic real structural feature. The high-resolution contrasts are characterized by lamellar fringes parallel to the (1 {\overline 1} 0 {\overline 1}) planes, and the quasi-kinematic diffraction patterns contain satellite peaks based on multiple scattering. All these phenomena can be interpreted by comparison of experimental and simulated data relying on a supercell approach.

The primary amine groups on the heptazine-based polymer melon, also known as graphitic carbon nitride (g-C3N4), can be replaced by urea groups using a two-step postsynthetic functionalization. Under simulated sunlight and optimum Pt loading, this urea-functionalized carbon nitride has one of the highest activities among organic and polymeric photocatalysts for hydrogen evolution with methanol as sacrificial donor, reaching an apparent quantum efficiency of 18% and nearly 30 times the hydrogen evolution rate compared to the nonfunctionalized counterpart. In the absence of Pt, the urea-derivatized material evolves hydrogen at a rate over four times that of the nonfunctionalized one. Since “defects” are conventionally accepted to be the active sites in graphitic carbon nitride for photocatalysis, the work here is a demonstrated example of “defect engineering,” where the catalytically relevant defect is inserted rationally for improving the intrinsic, rather than extrinsic, photocatalytic performance. Furthermore, the work provides a retrodictive explanation for the general observation that g-C3N4 prepared from urea performs better than those prepared from dicyandiamide and melamine. In-depth analyses of the spent photocatalysts and computational modeling suggest that inserting the urea group causes a metal-support interaction with the Pt cocatalyst, thus facilitating interfacial charge transfer to the hydrogen evolving centers.