Simple Stoichiometry Research Articles

Assessing Cu2+ active sites evolution on Cu-SSZ-13 NH3-SCR catalysts during hydrothermal aging: A transient response approach

Hydrothermal aging (HTA) conditions are commonly reached in Diesel engine NH3-SCR architectures based on Cu-CHA catalysts, altering the catalyst performance due to irreversible transformations of the catalytic sites. Relying on transient response methods (TRMs), we study two Cu-SSZ-13 samples with different HTA extents. The following conclusions apply: i) the Cu2+content is invariant with HTA; ii) the ZCu2+(OH)- population decreases concurrent to the increase of the Z2Cu2+ fraction and to iii) the loss of Brønsted acidity. This evidence agrees with the simple stoichiometry proposed for mild HTA processes: ZCu2+(OH)-+ZH+→Z2Cu2++H2O. Furthermore, TRMs permit to observe additional phenomena which comply with a low-T Cu2+-pair mediated reduction pathway recently proposed. The results from a comprehensive set of simple experimental flow reactor methods consolidate the proposed aging mechanism, strengthen the SCR reduction half cycle (RHC) mechanistic understanding and showcase TRMs as a viable alternative to more complex techniques for the characterization of Cu-CHA catalysts.

A comparative study of Nd15Fe78B7 and Nd15Co78B7 systems: phase formations and coercivity mechanisms

Both Nd-Fe-B and Nd-Co-B nanocrystalline magnets exhibit coercivity above 1 T. While the microstructure and mechanism of the coercive force of Nd-Fe-B magnets are well known, the Nd-Co-B system is much less studied, and the microstructure and origin of the high coercive state in this material is not well understood. In this work, we selected Nd15Fe78B7 and Nd15Co78B7 alloys with simple and stable stoichiometries to reveal the similarities and differences between these two systems. For this study, melt-spun nanocrystalline ribbons, hot-compacted magnets and bulk materials crystallized from the amorphous precursor were used. The coercivity of Nd15Fe18B7 alloy is in the range of 0.9–1.7 T, while for Nd15Co18B7 it was of 0.5–1.0 T. Electron microscopy and atom probe tomography analyses indicate that, in contrast to conventional Nd15Fe78B7, where the ferromagnetic Nd2Fe14B phase is the dominant matrix phase and the Nd-rich phase distributes along the grain boundaries providing magnetic decoupling, the Nd15Co18B7 alloys comprise of three randomly redistributed exchange-coupled ferromagnetic phases: Nd2Co14B, NdCo5 and NdCo4B. Single crystals of all constituent phases were grown and their spontaneous magnetization Ms and anisotropy constant K1 were determined. Using these measured intrinsic parameters and real nanostructure of Nd15Fe78B7 and Nd15Co78B7 alloys, micromagnetic simulations were carried out in order to reveal the differences in the coercivity mechanisms in these two distinctly different systems.

New insights in GeTe growth mechanisms

The compound GeTe, despite its simple stoichiometry, is rather unconventional and has been investigated both from a fundamental and technological perspective: it is of high interest for several technologies such as data-storage (phase change memories) and thermoelectricity. The understanding of GeTe growth is thus a key issue for technological applications and fundamental understanding. In this work, GeTe crystallization kinetics is compared to Ge/Te reactive diffusion kinetics using in situ X-ray diffraction measurements, as well as in situ transmission electron microscopy. GeTe crystallization from an amorphous solid solution exhibiting the stoichiometry of the compound GeTe is found to occur at the same temperature as for the reactive diffusion of an amorphous Ge layer on top of a polycrystalline Te layer. Furthermore, GeTe growth is of tridimensional type in the two cases, and can be modeled by the Johnson-Mehl-Avrami-Kolmogorov model. Using this model, the activation energies of nucleation and growth were determined for both crystallization and reactive diffusion. The results suggest that GeTe exhibits nucleation/reaction kinetics unusually low compared to atomic transport kinetics, contrasting with other germanides.

Designing a Li-N-H Based Solid Electrolyte

All-solid-state-batteries (ASSBs) have long promised to be the next-generation of high-performance energy storage devices, with a step-change in energy density, stability and cell safety touted as potential advantages compared to conventional Li-ion battery cells.[1] The development of fast lithium-ion conductors is key to realising commercially-viable ASSBs, however significant challenges remain with the leading candidate materials. Complex metal hydrides, in particular BH4 - derived materials, have gained recent attention due to their high ambient temperature lithium ionic conductivities and good stability with lithium metal.[2] Nitrogen-based complex hydrides, such as materials within the Li-N-H system, have largely been studied as solid-state hydrogen stores. However, a key characteristic that links the impressive properties of the Li-N-H system in this application is the high Frenkel defect-based Li-ion conductivity, which facilitates the formation of amide-imide and imide-nitride-hydride antifluorite structured solid solutions.[3,4] These solid solutions represent an opportunity through careful stoichiometry control to tailor the properties of a Li-N-H based material for application as a solid electrolyte.Careful characterisation using X-ray diffraction and Raman measurements have allowed us to evaluate the structure of the solid solutions between lithium imide (Li2NH), lithium amide (LiNH2) and lithium nitride hydride (Li4NH), all dominated by a disordered anti-fluorite phase. We demonstrate the ability to tailor the conductivity of these materials between an ionic insulator and a superionic conductor by simple stoichiometry control. Lithium imide, and stoichiometries close to this compound, in particular display favourable properties as solid electrolyte materials. We herein exhibit the first demonstration of a Li-N-H material in an ASSB, with the materials displaying high lithium ion conductivities, wide electrochemical stability windows and potential for further tuning for this application.Ultimately, these results identify Li-N-H based complex hydrides as an interesting avenue of research for solid electrolyte application that is yet to be fully explored. We hope this presentation will highlight these materials and spark further development such as has been seen for oxide and sulphide based fast-ion conductors.1) Z. Zhang, Y. Shao, B. Lotsch, Y. Hu, H. Li, J. Janek, L F. Nazar, C. Nan, J. Maier, M. Armand and L. Chen, Energy Environ. Sci., 2018, 11, 1945-19762) A. Unemoto, M. Matsuo, and S. Orimo, Adv. Funct. Mater., 2014, 24, 2267-22793) W. Li, G. Wu, C. M. Araujo, R. H. Scheicher, A. Blomqvist, R. Ahuja, Z. Xiong, Y. Fengb and P. Chen, Energy Environ. Sci., 2010, 3, 1524-15304) J. W. Makepeace, J. M. Brittain, A. S. Manghnani, C. A. Murray, T. J. Wood and W. I. F. David, Phys. Chem. Chem. Phys., 2021, 23, 15091 Figure 1

Perovskite solar cells from the viewpoint of innovation and sustainability.

Innovation is essential around the themes of climate change and sustainability. Commercial photovoltaics (PV) have noticeably contributed to getting to 22.1% share of the gross final energy consumption in Europe from renewable sources in 2020 but a steep further increase is urgent in the near future. Over the last few years, great success has been achieved by perovskites applied to PV, with mixed anions and cations in shared lattices that reached record efficiency values close to those of Si in laboratory-scale solar cells (∼26%). Their use has recently shed light on a medium/long-term compositional instability that arises from the partial miscibility of the species with similar role in the atomic lattice. The chemical route to prepare the materials for Perovskite Solar Cells (PSCs) also needs to be critically reviewed. Material waste and reuse are other concerns to be faced. This perspective paper indeed tackles some aspects for innovation and sustainability on the PSC field for production purposes. Some hints for technologically affordable processes based on in-vacuum deposition of Perovskites are provided in light of their sustainability and for the need to reduce production/maintenance costs. It is also discussed how to make in-vacuum production further competitive by boosting the material quality. Innovation is also projected into the theme of making sustainable choices for device architectures and materials. Carbon-based PSCs are highly focused since they allow avoiding the use of complex, unstable and costly HTLs. From the material side, pros and cons of using fully inorganic CsPbI3 are commented, framed by the current revival of single-cation perovskites. CsPbI3, in particolar, enables recycling and reuse initiatives thanks to the overall mass preservation under degradation. Some closing remarks are provided on the safe use of Pb as its effective sequestration before release from the PSC into the environment is properly engineered. We lastly trust that initiatives bringing together academic and industrial know-how in complementary fields able to take up responsible innovation will contribute to accelerating the ecological transition and will enable the societal transformation to fulfil the 2050 EU agenda for a sustainable future.

Synthesis, Microstructure and Properties of Magnetron Sputtered Lead Zirconate Titanate (PZT) Thin Film Coatings

Compared to aluminum nitride (AlN) with simple stoichiometry, lead zirconate titanate thin films (PZT) are the other promising candidate in advanced micro-electro-mechanical system (MEMS) devices due to their excellent piezoelectric and dielectric properties. The fabrication of PZT thin films with a large area is challenging but in urgent demand. Therefore, it is necessary to establish the relationships between synthesis parameters and specific properties. Compared to sol-gel and pulsed laser deposition techniques, this review highlights a magnetron sputtering technique owing to its high feasibility and controllability. In this review, we survey the microstructural characteristics of PZT thin films, as well as synthesis parameters (such as substrate, deposition temperature, gas atmosphere, and annealing temperature, etc.) and functional proper-ties (such as dielectric, piezoelectric, and ferroelectric, etc). The dependence of these influential factors is particularly emphasized in this review, which could provide experimental guidance for researchers to acquire PZT thin films with expected properties by a magnetron sputtering technique.

Measurement of Superconductivity and Edge States in Topological Superconductor Candidate TaSe3 Supported by the National Key R&D Program of China (Grant No. 2017YFA0305400), the Shanghai Technology Innovation Action Plan 2020-Integrated Circuit Technology Support Program (Grant No. 20DZ1100605), the National Natural Science Foundation of China (Grant Nos. 52072168, 21733001, 51861145201, U1932217, and 11974246), the National Key Basic Research Program of China

Topological superconductors (TSCs) have been widely investigated in recent years due to their novel physics and ability to host Majorana fermions (MFs) which are key to topological quantum computation. Despite the great interest, only a few compounds have been proposed as candidates of intrinsic TSCs, such as iron-based superconductor FeSe0.55Te0.45 and 2M-WS2. Among them, quasi-one-dimensional superconductor TaSe3 possesses fascinating properties such as its simple stoichiometry, layered nature and chemical stability. Here, using scanning tunneling microscope/spectroscopy (STM/STS), we systematically investigate the topography and electronic structure of TaSe3. Our STM/STS measurement reveals large atomically flat, defect-free surfaces suitable for the search of MF; electronic density of states consistent with our angle-resolved photoemission result and band-structure calculations, and a uniform superconducting gap with a typical size of ∼ 0.25 meV. Remarkably, additional edge states are observed in the vicinity of the terrace edge, suggesting they may have a topological origin. Our result proves the coexistence of superconductivity and topological electronic structure in TaSe3, making it an intriguing platform to investigate topological superconductivity.

Crystal and Electronic Structures of Palladium Sesquichalcogenides

Despite having a relatively simple binary stoichiometry, palladium sesquichalcogenides [i.e., Pd2Q3 (Q = O, S, Se, Te)] are absent in the reported Pd–Q phase diagrams. To search for the possibility...

Copper in Coloradoite, HgTe: Actual State or Analytical Artifact?

Chemical and structural data of two Cu-rich coloradoite crystals from Kalgoorlie, Australia, are reported. Two grains with simple stoichiometries, i.e., Hg1 – xCuxTe with x ~0.30, and ~0.22, were characterized by single-crystal X-ray diffraction and electron-probe microanalysis. In the absence of single-crystal data it might be tempting to hypothesize that the presence of large amounts of other elements can induce some ordering leading to distinct mineral species. However, structural analyses show that all of the phases are cubic and crystallize in the space group $$F\overline 4 3m$$ . On the basis of information gained from the chemical and structural characterization it can be concluded that there is a complete solid solution between coloradoite and a possible, still unknown, Cu-coloradoite in nature.

Quantifying Protein-Protein Interactions by Molecular Counting with Mass Photometry.

Interactions between biomolecules control the processes of life in health and their malfunction in disease, making their characterization and quantification essential. Immobilization‐ and label‐free analytical techniques are desirable because of their simplicity and minimal invasiveness, but they struggle with quantifying tight interactions. Here, we show that mass photometry can accurately count, distinguish by molecular mass, and thereby reveal the relative abundances of different unlabelled biomolecules and their complexes in mixtures at the single‐molecule level. These measurements determine binding affinities over four orders of magnitude at equilibrium for both simple and complex stoichiometries within minutes, as well as the associated kinetics. These results introduce mass photometry as a rapid, simple and label‐free method for studying sub‐micromolar binding affinities, with potential for extension towards a universal approach for characterizing complex biomolecular interactions.

Quantifying Protein–Protein Interactions by Molecular Counting with Mass Photometry

AbstractInteractions between biomolecules control the processes of life in health and their malfunction in disease, making their characterization and quantification essential. Immobilization‐ and label‐free analytical techniques are desirable because of their simplicity and minimal invasiveness, but they struggle with quantifying tight interactions. Here, we show that mass photometry can accurately count, distinguish by molecular mass, and thereby reveal the relative abundances of different unlabelled biomolecules and their complexes in mixtures at the single‐molecule level. These measurements determine binding affinities over four orders of magnitude at equilibrium for both simple and complex stoichiometries within minutes, as well as the associated kinetics. These results introduce mass photometry as a rapid, simple and label‐free method for studying sub‐micromolar binding affinities, with potential for extension towards a universal approach for characterizing complex biomolecular interactions.

Multiphase carbon mineralization for the reactive separation of CO2 and directed synthesis of H2.

There is a need to capture, convert and store CO2 by atom-efficient and energy-efficient pathways that use as few process configurations as possible. This need has motivated studies into multiphase reaction chemistries and this Review describes two such approaches in the context of carbon mineralization. The first approach uses aqueous alkaline solutions containing amine nucleophiles that capture CO2 and eventually convert it into calcium and magnesium carbonates, thereby regenerating the nucleophiles. Gas-liquid-solid and liquid-solid configurations of these reactions are explored. The second approach combines silicates such as CaSiO3 or Mg2SiO4 with CO and H2O from the water-gas shift reaction to give H2 and calcium or magnesium carbonates. Coupling carbonate formation to the water-gas shift reaction shifts the latter equilibrium to afford more H2 as part of a single-step catalytic approach to carbon mineralization. These pathways exploit the vast abundance of alkaline resources, including naturally occurring silicates and alkaline industrial residues. However, simple stoichiometries belie the complex, multiphase nature of the reactions, predictive control of which presents a scientific opportunity and challenge. This Review describes this multiphase chemistry and the knowledge gaps that need to be addressed to achieve 'step-change' advancements in the reactive separation of CO2 by carbon mineralization.

Synergistic Solvent Extraction Is Driven by Entropy.

In solvent extraction, the self-assembly of amphiphilic molecules into an organized structure is the phenomenon responsible for the transfer of the metal ion from the aqueous phase to the organic solvent. Despite their significance for chemical engineering and separation science, the forces driving the solute transfer are not fully understood. Instead of assuming the simple complexation reaction with predefined stoichiometry, we model synergistic extraction systems by a colloidal approach that explicitly takes into account the self-assembly resulting from the amphiphilic nature of the extractants. Contrary to the current paradigm of simple stoichiometry behind liquid-liquid extraction, there is a severe polydispersity of aggregates completely different in compositions, but similar in the free energy. This variety of structures on the nanoscale is responsible for the synergistic transfer of ions to the organic phase. Synergy can be understood as a reciprocal effect of chelation: it enhances extraction because it increases the configurational entropy of an extracted ion. The global overview of the complex nature of a synergistic mixture shows different regimes in self-assembly, and thus in the extraction efficiency, which can be tuned with respect to the green chemistry aspect.

Computational Design of Mixed-Valence Tin Sulfides as Solar Absorbers.

Binary tin sulfides, such as SnS and SnS2, are appealing because of their simple stoichiometry and semiconducting properties and are, therefore, being pursued as potentially cost-effective materials for optoelectronic applications. The multivalency of Sn, that is, Sn(+2) and Sn(+4) allows yet more intermediate compositions, SnxSy, whose structures and properties are of interest. Sn2S3 is already under consideration as a mixed-valence semiconductor. Other intermediate compositions, for example, Sn3S4 and Sn4S5 have remained elusive, although their existences have been alluded to in literature. Here we report a comprehensive study of phase stability of the SnxSy series compounds, utilizing swarm-intelligence crystal structure search method combined with first-principles energetic calculations. We find that the stability of mixed-valence SnxSy compounds with respect to decomposition into pure-valence SnS and SnS2 is in general weaker than the SnxOy counterparts, likely due to differences in chemical bonding. Besides identifying the experimentally discovered stable phases of Sn2S3, our calculations indicate that the Sn3S4 phase is another mixed-valence composition which shows marginal stability with respect to decomposition into SnS and SnS2. Other studied compositions may be metastable under ambient conditions, with slightly positive formation enthalpies. We find two structures of Sn3S4 having comparably low energies, both of which feature one-dimensional chain-like fragments obtained by breaking up the edge-connected octahedral layers of SnS2. Both structures indicate lattice phonon stability and one shows quasi-direct band gap with a calculated value of 1.43 eV, ideal for solar absorbers. A further analysis of the composition-structure-property relationship supports the notion that low-dimensional Sn-S motifs and van der Waals interaction may lead to diverse structure types and chemical compositions, having functional properties that are yet to be identified in the SnxSy series with mixed valency.

Ion quantification in liposomal drug products using high performance liquid chromatography

A simple, straightforward analytical method based on liquid chromatography has been optimized to quantify total, internal, and external ions in drug-loaded liposomal products. The quantification of ammonium and sulfate ions in Doxil is detailed; although, the methodology has been extrapolated to quantitate a variety of ions, including calcium, acetate, and others in several different liposomal formulations. Total ion concentrations were measured after disruption of the liposome via lyophilization, to liberate all components. External ion concentrations were made following membrane centrifugation, without disruption of the liposome structure, where the permeate fraction was analyzed for external ion quantities. The internal ion fraction was derived from mass balance of the total and external ion measurements. High performance liquid chromatography (HPLC), equipped with different separation columns, and coupled to a charged aerosol detector, was employed for all ion quantifications. The analytical measurements were confirmed using simple stoichiometry based on the drug crystallization of doxorubicin within the liposome interior. The method presented herein is quick, highly accurate, and has significantly improved lower limits of detection and quantification over other traditional methods. As more follow-on versions of Doxil are being developed, this facile approach to ion quantitation can be used to help establish compositional similarity to the reference listed drug.

Fabrication of Tin Oxide Thin Film Transistors by RF Magnetron Sputtering Using Sn/SnO Composite Target

P-type tin oxide thin film deposited by RF sputtering for transparent thin film transistor (TFT) applications is the subject of this study. P-type tin oxide thin film can be made by doping a cation with a lower valence into n-type SnO 2 as an acceptor impurity or by fabrication with tin monoxide (SnO). The later method was investigated in this study by RF magnetron sputtering process, which has a high deposition rate, uniform thickness control, simple stoichiometry control, and reproducibility. A Sn/SnO composite target was used in RF sputtering to utilize the benefits of both metallic and ceramic sputtering targets. A Sn/SnO composite target is expected to provide p-type tin oxide thin films that are easier to manufacture than metallic target or ceramic target. The metallic Sn element provides an excellent control of structural defects, while the ceramic SnO element provides stable stoichiometry. The p-type tin oxide thin film with a Sn/SnO composite target showed very good transparency of ~95%. and excellent electrical properties. The p-type tin oxide thin film of 15nm thickness had a carrier concentration of 8.03X10 15 cm -3 and a mobility of 15.2cm 2 /Vs. With these ultrathin tin oxide films, a p-channel TFT was fabricated with a staggered bottom-gate structure, and the effect of different channel thicknesses and different distances between the two electrodes were evaluated. The tin oxide TFT with a thick p-channel layer showed a significant increase in current measured than the tin oxide with a thin p-channel layer. The current measured tended to increase greatly as the distance between electrodes decreased. The IV output curves of the tin oxide TFTs exhibited characteristics of bipolar transistors potentially due to the partial creation of the oxygen-deficient SnO 2 like structure, but the mechanism of bipolar transistor characteristics from the p-channel tin oxide TFT is still unclear. The fabrication of highly transparent tin oxide thin film with bipolar transistor characteristics is demonstrated herein.

Breaking Compromises in CO2 Reduction

Electrochemical reduction of CO 2 to formate is a promising approach to utilize intermittent renewable energy for high-value chemical storage and to mitigate carbon pollution. Demanding applied targets for this process require that the reaction is sustained at a high current density with near-unity product efficiency. In this issue of Joule , Zheng and De Luna et al. show that incorporating sulfur into tin catalysts greatly increases the reaction rate while maintaining high selectivity and robust stability.

Hg(II) sensing platforms with improved photostability: The combination of rhodamine derived chemosensors and up-conversion nanocrystals

This paper reported two nanocomposite sensing platforms for Hg(II) detection with improved photostability, using two rhodamine derivatives as chemosensors and up-conversion nanocrystals as excitation host, respectively. There existed a secondary energy transfer from this excitation host to these chemosensors, which was confirmed by spectral analysis, energy transfer radius calculation and emission decay lifetime comparison. In this case, chemosensor photostability was greatly improved. Further analysis suggested that these chemosensors recognized Hg(II) following a simple binding stoichiometry of 1:1. Hg(II) sensing performance of these sensing platforms was analyzed through their emission spectra upon various Hg(II) concentrations. Emission spectral response, Stern-Volmer equation, emission stability and sensing selectivity were discussed in detail. It was finally concluded that these chemosensors showed emission turn on effect towards Hg(II), with high photostability, good selectivity and linear response.

Agricultural Mineral Additives for Passive Nitrate Removal in Septic Systems

Processes for removing sewage nitrogen at the individual residential scale must be low-maintenance with only annual service visits. A passive autotrophic process in an upflow configuration, using a 50-50 mixture by volume of: (a) agricultural sulfur for nitrate reduction, and (b) agricultural limestone for pH adjustment, was field-tested at 8 – 34 hours hydraulic retention times (HRT) at one site and at 14 hours HRT at another. An HRT of 8 – 12 hours was found to be the minimum without substantial nitrate breakthrough; pH was fully neutralized and little BOD and TSS addition resulted. About 90 – 95% of total nitrogen was removed in the two field study sites. The positive correlation of ‘mass of sulfate formed’ versus ‘mass of nitrate + oxygen removed’ reflects a simple stoichiometry, though possibly requiring ammonium to be included. Intercepts of the correlation near the origin suggest that gypsum is not precipitated in the process.

Brannerite, UTi2O6: Crystal chemistry, synthesis, properties, and use for actinide waste immobilization

The host materials suggested for immobilization of actinide waste of military or civil origin often contain the secondary (U,Pu)Ti2O6 phase of brannerite structure. For example, the materials for incorporation of excess plutonium, mainly consisting of pyrochlore, contain up to 30% brannerite. This is a usual phase in titanate host materials for isolating spent nuclear fuel (SNF) and products of its reprocessing, including waste from production of 99mТс for medical purposes and other kinds of waste with high U and Pu content. Despite simple ideal stoichiometry, brannerite can contain large amounts of rare earths. This feature is due to the presence of uranium not only in the 4+ oxidation state, but also in the 5+ and 6+ states, which favors the exchange of rare earth elements (REE), e.g., in accordance with the scheme 2U4+ ↔ U5+ + REE3+. The REE amount in brannerite reaches 0.5–0.7 atom per formula unit. Therefore, brannerite is of interest as a host material for the rare earth–actinide fraction of high-level waste (HLW). To evaluate the prospects for such use of brannerite, data on the radiation resistance of brannerite and its behavior in aqueous solutions are analyzed. In these properties, brannerite is inferior to pyrochlore and zirconolite. The rate of actinide leaching from brannerite is higher by an order of magnitude than from these phases, but lower by 3–4 orders of magnitude than from glass host materials. Natural brannerite is stable in media with weakly alkaline and reducing waters. Therefore, brannerite seems suitable for immobilization of rare earth–actinide waste. This host material can be synthesized by sintering or cold crucible induction melting followed by crystallization.