Control Of Stoichiometry Research Articles

Controlling inversion disorder in a stoichiometric spinel magnet

In the study of frustrated quantum magnets, it is essential to be able to control the nature and degree of site disorder during the growth process, as many measurement techniques are incapable of distinguishing between site disorder and frustration-induced spin disorder. Pyrochlore-structured spinel oxides can serve as model systems of geometrically frustrated three-dimensional quantum magnets; however, the nature of the magnetism in one well-studied spinel, ZnFe2O4, remains unclear. Here, we demonstrate simultaneous control of both stoichiometry and inversion disorder in the growth of ZnFe2O4 single crystals, directly yielding a revised understandingof both the collective spin behavior and lattice symmetry. Crystals grown in the stoichiometric limit with minimal site inversion disorder contravene all the previously suggested exotic spin phases in ZnFe2O4. Furthermore, the structure is confirmed on the [Formula: see text] space group with broken inversion symmetry that induces antiferroelectricity. The effective tuning of magnetic behavior by site disorder in the presence of robust antiferroelectricity makes ZnFe2O4 of special interest to multiferroic devices.

On-line implementation of model free controller for oxygen stoichiometry and pressure difference control of polymer electrolyte fuel cell

This paper proposes and validates a model free controller to improve the real time operating conditions of Proton Exchange Membrane Fuel Cells (PEMFC). This approach is based on an ultra-local model that does not depend on a precise knowledge of the system. It is perfectly adapted to a complex system such as the fuel cell, while benefiting from the ease of online implementation and low computational cost. The designed controller is used to regulate both the oxygen stoichiometry and the membrane inlet pressure, which are crucial operating conditions for the fuel cell's lifetime. The objectives of the proposed control strategy are twofold: preventing the starvation failure, and limiting the potential for mechanical degradation of the membrane during a large pressure difference. The performance of the proposed control strategy is initially evaluated by a simulation environment for both oxygen stoichiometry and inlet pressure difference control of fuel cell stack. An online validation on 1.2 KW fuel cell stack is conducted to control the membrane pressure drop. Two case studies are comprehensively investigated in relation to stoichiometry control: set point tracking and rejection of unmeasured disturbances caused by current variations. Simulations and experimental results reveal that the proposed controller provides significantly better performance in terms of fast trajectory tracking, and ensures less overshoot compared to the Fuzzy PID and PID controller. This efficiency is proven using the Integral Absolute Error (IAE), Integral Squared Error (ISE) and Integral of the Square input (ISU) performance indexes.

Regioselectivity Switch Based on the Stoichiometry: Stereoselective Synthesis of Trisubstituted Vinyl Epoxides by Cu‐Catalyzed 3‐exo‐trig Cyclization of α‐Allenols

AbstractTypical transition metal‐catalyzed oxycyclization of allenols takes place at the terminal allene carbon via a 5‐endo path and forms dihydrofurans. A copper‐catalyzed protocol brought about a reversed regioselectivity, generating a series of trisubstituted epoxides through a 3‐exo‐cyclization/sulfonylation cascade. The current stoichiometry control of regioselectivity may open singular opportunities in chemical transformations.magnified image

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

Observation of bandgap closing in SrxBa1−xBiO3 films: Evidence toward topological order in BaBiO3

Sr x Ba 1 − x BiO 3 (0≤x<0.5) films were fabricated from solution-phase precursors using flow-limited field-injection electrostatic spraying to investigate the predicted topological properties of BaBiO3, an oxide perovskite. The films were analyzed via x-ray diffraction, optical conductivity, and Raman spectroscopy. The bandgaps measured by optical absorption spectroscopy were in line with the predicted value of SrxBa1−xBiO3 for x<0.25, decreasing with an increase in x to reach zero at x=0.348. This suggests that BaBiO3 may have topological order and that, upon appropriate doping, it may be used as a topological insulator or superconductor in quantum-computing devices. This work may open up new avenues toward engineering of topological insulators with precise and reproducible control of stoichiometry, obviating extreme deposition temperatures or vacuum processing.

Kinetic Control of Anion Stoichiometry in Hexagonal BaTiO3

The cubic oxyhydride perovskite BaTiO3−xHx, where the well-known ferroelectric oxide BaTiO3 is partially hydridized, exhibits a variety of functions such as being a catalyst and precursor for the synthesis of mixed-anion compounds by utilizing the labile nature of hydride anions. In this study, we present a hexagonal version, BaTi(O3−xHx) (x < 0.6) with the 6H-type structure, synthesized by a topochemical reaction using hydride reduction, unlike reported hexagonal oxyhydrides obtained under high pressure. The conversion of cubic BaTiO3 (150 nm) to the hexagonal phase by heat treatment at low temperature (950~1025 °C) using a Mg getter allows the introduction of large oxygen defects (BaTiO3−x; x − 0.28) while preventing the crystal growth of hexagonal BaTiO3, which has been accessible at high temperatures of ~1500 °C, contributing to the increase of the hydrogen content. Hydride anions in 6H-BaTiO3−xHx preferentially occupy face-sharing sites, as do other oxyhydrides.

Physiological Functions of Intracellular Protein Degradation.

While cellular proteins were initially thought to be stable, research over the last decades has firmly established that intracellular protein degradation is an active and highly regulated process: Lysosomal, proteasomal, and mitochondrial degradation systems were identified and found to be involved in a staggering number of biological functions. Here, we provide a global overview of the diverse roles of cellular protein degradation using seven categories: homeostasis, regulation, quality control, stoichiometry control, proteome remodeling, immune surveillance, and baseline turnover. Using selected examples, we outline how proteins are degraded and why this is functionally relevant.

Improved electrocatalytic activity of copper (I) oxide electrodeposited on graphite carbon

Due to its abundance and low cost, Cu2O is an attractive electrocatalyst for the water treatment. The electrodeposition is an attractive technique, because of its simplicity, low cost and possibility of making large area as thin homogeneous film of Cu2O with good quality of nanoparticles. This study reports the electrode position of Cu2O thin uniform film which offers the advantages of precise stoichiometry and thickness control (δ = 5.11 μm). The uniform and well-adhered Cu2O red thin film electrodeposited on graphite carbon is used for the electrodegradation of the crystal violet dye (CVD). The gap value is equivalent to 2.02 eV calculated from spectral UV-visible, this value agrees with the red color and indicates semi-conductive properties. A potential Efb equal to 0.43 V and acceptors density of 1.14. 2019 cm-3 and p-type conductivity were determined by the Mott- Schottky measurement. This fact makes Cu2O a good candidate for electrocatalytic activity, pH =7, 25°C temperature, 1.6 V applied voltage and 180 min electrolysis. Cu2O was used to degrade CVD (10 mg /L) via an electrochemical technique. Pseudo-first order kinetics governed the electrochemical decomposition.

The modulated oxygen evolution reaction performance in La2/3Sr1/3CoO3 by a design of stoichiometry offset

The accurate stoichiometry control of single-crystalline transition metal oxide thin film and the electrochemical performance such as in oxygen evolution reaction (OER) offer a useful pathway towards the mechanism understanding and the strategy of improving electrochemical activity at the atomic level. As a stable, low cost, and high active OER catalyst, La2/3Sr1/3CoO3 (LSCO) has drawn substantial attention recently. Here we report a modulated OER performance of LSCO by different stoichiometry offsets, an overall ∼2074.63% tunability can be seen. Meanwhile, the overpotential of LSCO exhibits a volcano trend as a function of oxygen concentration. These phenomena can be understood on the competition of double- and super-exchanges in Co3+/Co4+ with the help of the overlap of O 2p and Co 3d orbits. Our investigation provides an effective platform for obtaining a narrow window of improved electrochemical activity in correlated transition metal oxides.

Canonical approach to cation flux calibration in oxide molecular-beam epitaxy

Molecular-beam epitaxy (MBE) is the gold standard for the epitaxial growth of complex oxides with the best material properties as determined by respective figures of merit. Unfortunately, once more than one cation is involved in the material desired, MBE growth often becomes plagued by difficulties in stoichiometry control. Instead of relying on a quartz crystal microbalance to measure the fluxes of the individual molecular beams, which lacks accuracy, or reflection high-energy electron diffraction oscillations of the targeted multication oxide in layer-by-layer growth, which lacks general applicability, here, we describe a canonical approach based on the growth of films of the constituent binary oxides or metals individually for cation flux calibration. This method can calibrate the flux of each molecular beam with an absolute accuracy of \ifmmode\pm\else\textpm\fi{}1%. After describing the growth parameters of binary oxides or metals enabling the individual fluxes of 39 elements of the periodic table to be determined, we demonstrate the efficacy of this approach by applying it to the growth of the quaternary ferromagnetic metal ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ to achieve films with transport properties rivalling the best reported using thin-film growth techniques providing stoichiometric transfer.

Novel Method for the Growth of Two-Dimensional Layered InSe Thin Films on Amorphous Substrate by Molecular Beam Epitaxy

A two-dimensional (2D) material known as indium selenide (InSe) is widely considered a promising layered semiconductor with potential applications in electronics and optoelectronics. However, the single phase of InSe is still a challenge due to the close formation energy of InSe and In2Se3. In this study, we demonstrate a novel growth method for 2D InSe with an indium precursor layer by molecular beam epitaxy. Indium pre-deposited on substrate at room temperature followed by growth of InSe at 550°C can overcome the problem of stoichiometry control and can be applied on amorphous substrate with high quality. According to Raman scattering spectra, X-ray diffraction, and high-resolution transmission electron microscopy results, we find that 2D InSe phase can be facile formed under both indium-rich and -poor conditions. The pre-deposited indium precursor effectively induces replacement with subsequent Se and In atoms to form the InSe phase while suppressing the In2Se3 phase. Additionally, this single phase InSe is stable in the atmosphere, exhibiting superior electronic properties even after over 100 days exposure. Recently, this method has been successfully applied to a flexible substrate, such as aluminum foil, resulting in reliable InSe quality. Our results demonstrate an innovative and forward-looking approach to developing 2D InSe material.

Stoichiometry control and automated growth of alkali antimonide photocathode films by molecular beam deposition

We report on a method of photoemissive film growth that controls stoichiometry in real time. We show that stoichiometry control using a feedback loop is possible because (a) photoemissive properties exhibit a distinct dependence on the stoichiometric composition and (b) stoichiometric composition strongly depends on the ratio of the incident fluxes. The reported results were obtained on Cs3Sb but are expected to be relevant to other alkali antimonides and tellurides.

The changes in plant and soil C pools and their C:N stoichiometry control grassland N retention under elevated N inputs.

Nitrogen (N) retention is a critical ecosystem function for maintaining soil fertility and mitigating pollution caused by anthropogenic N input. However, it has not yet been elucidated how responses of plant and soil regulate ecosystem N retention. Here, we combined a 14-year N addition experiment in a temperate steppe with a global meta-analysis in grasslands, to assess changes in carbon (C) pool size and stoichiometric C:N ratio of plant and soil components and evaluate the contribution of each component to grassland N retention under increasing N levels. We found that N addition increased N storage in the plant pool by stimulating biomass production and reducing tissue C:N at the community level. However, the non-random loss of forbs and legumes associated with a low C:N ratio partially offset the decline in community-level C:N ratio, thereby diminishing the positive net effect of N enrichment on plant N storage. The observed increase in soil N storage was predominantly determined by the decrease in C:N ratio of topsoil, while no changes were detected in the subsoil. On 14-year time scale, the upper limitation of N retention capacity in our study site was 167.02 g N/m2 . Global meta-analysis further indicated that a decade's N addition significantly increased the N storage in shoot, root and topsoil through enhancing the C pool and decreasing the C:N ratio, while did not affect those of subsoil. However, the positive correlation between the response of subsoil N storage and treatment duration further indicates that, though the accumulation of added N lagged behind that of topsoil, subsoil could play an important role in N retention on a longer time scale. Our study demonstrated that the enhanced plant productivity and altered physiological metabolism indicated by the decreased C:N ratio jointly determined grassland ecosystem N retention. The capacity of the grassland ecosystem to retain exogenous N input is limited, especially for a large amount of N input that occurs in a short period. However, in the context of chronically rising N deposition, the long-term N retention capacity of grasslands should largely depend on the response of subsoil, especially after topsoil N is saturated.

Control of subunit stoichiometry in single-chain MspA nanopores

Transmembrane protein channels enable fast and highly sensitive detection of single molecules. Nanopore sequencing of DNA was achieved using an engineered Mycobacterium smegmatis porin A (MspA) in combination with a motor enzyme. Due to its favorable channel geometry, the octameric MspA pore exhibits the highest current level compared with other pore proteins. To date, MspA is the only protein nanopore with a published record of DNA sequencing. While widely used in commercial devices, nanopore sequencing of DNA suffers from significant base-calling errors due to stochastic events of the complex DNA-motor-pore combination and the contribution of up to five nucleotides to the signal at each position. Different mutations in specific subunits of a pore protein offer an enormous potential to improve nucleotide resolution and sequencing accuracy. However, individual subunits of MspA and other oligomeric protein pores are randomly assembled in vivo and in vitro, preventing the efficient production of designed pores with different subunit mutations. In this study, we converted octameric MspA into a single-chain pore by connecting eight subunits using peptide linkers. Lipid bilayer experiments demonstrated that single-chain MspA formed membrane-spanning channels and discriminated all four nucleotides identical to MspA produced from monomers in DNA hairpin experiments. Single-chain constructs comprising three, five, six, and seven connected subunits assembled to functional channels, demonstrating a remarkable plasticity of MspA to different subunit stoichiometries. Thus, single-chain MspA constitutes a new milestone in the optimization of MspA as a biosensor for DNA sequencing and many other applications by enabling the production of pores with distinct subunit mutations and pore diameters.

NiFe]-(Oxy)Sulfides Derived from NiFe2O4 for the Alkaline Hydrogen Evolution Reaction

The development of noble-metal-free electrocatalysts is regarded as a key factor for realizing industrial-scale hydrogen production powered by renewable energy sources. Inspired by nature, which uses Fe- and Ni-containing enzymes for efficient hydrogen generation, Fe/Ni-containing chalcogenides, such as oxides and sulfides, received increasing attention as promising electrocatalysts to produce hydrogen. We herein present a novel synthetic procedure for mixed Fe/Ni (oxy)sulfide materials by the controlled (partial) sulfidation of NiFe2O4 (NFO) nanoparticles in H2S-containing atmospheres. The variation in H2S concentration and the temperature allows for a precise control of stoichiometry and phase composition. The obtained sulfidized materials (NFS) catalyze the hydrogen evolution reaction (HER) with increased activity in comparison to NFO, up to −10 and −100 mA cm−2 at an overpotential of approx. 250 and 450 mV, respectively.

Cover Feature: The Mechanistic Perspective of IV Iodoxolones (Asian J. Org. Chem. 1/2022)

This multidisciplinary literature review traces the historical emergence of IV iodoxolones as a comprehensive catalogue of the plausible reaction mechanisms. The versatile mild oxidants are a key to unlock the green chemistry future, delivering up to quantitative yields in regioselective O-atom transfer or condensative dehydrogenation under mild reaction conditions at relatively low cost, free from heavy metal contamination or toxic waste. Learn or revisit how control of stoichiometry, temperature and solvent system enabled scientists to leverage chemoselective oxidations by unpacking the cornucopia of IV iodoxolone chemistry. More information can be found in the Review by Antony Chipman.

Modifying the internal substituents of self-assembled cages controls their molecular recognition and optical properties.

Self-assembled Fe4L6 cage complexes with variable internal functions can be synthesized from a 2,7-dibromocarbazole ligand scaffold, which orients six functional groups to the cage interior. Both ethylthiomethylether and ethyldimethylamino groups can be incorporated. The cages show strong ligand-centered fluorescence emission and a broad range of guest binding properties. Coencapsulation of neutral organic guests is favored in the larger, unfunctionalized cage cavity, whereas the thioether cage has a more sterically hindered cavity that favors 1 : 1 guest binding. Binding affinities up to 106 M-1 in CH3CN are seen. The dimethylamino cage is more complex, as the internal amines display partial protonation and can be deprotonated by amine bases. This amine cage displays affinity for a broad range of neutral organic substrates, with affinities and stoichiometries comparable to that of the similarly sized thioether cage. These species show that simple variations in ligand backbone allow variations in the number and type of functions that can be displayed towards the cavity of self-assembled hosts, which will have applications in biomimetic sensing, catalysis and molecular recognition.

Alterations in Substrate Stoichiometry Control the Responses of Soil Diazotrophs to Nutrient Enrichment

Alterations in Substrate Stoichiometry Control the Responses of Soil Diazotrophs to Nutrient Enrichment

Influence of the synthesis parameters on the transport properties of Mg2Si0.4Sn0.6 solid solutions produced by melting and spark plasma sintering

In this work, the influence of the preparation route on the structural, morphological, and thermoelectric properties of the Mg2Si0.4Sn0.6 solid solutions is investigated. The synthesis based on melting the constituent elements in a closed graphite crucible followed by spark plasma sintering allows mixing elements with a large difference of their melting temperatures and a good control of sample stoichiometry. The optimized synthesis route is validated by the doped V and Sb samples, which yield good thermoelectric performance. The n-type doping leads to two orders of magnitude increase of the carrier concentration, and thus a subsequent increase of the electrical conductivity, which, in turn, augments greatly the power factor of the Mg1.98V0.02Si0.385Sn0.6Sb0.015 to 42.61 x10−4 Wm−1K−2 at 650K. Although doping slightly enlarges the thermal conductivity, a peak value of the figure of merit ZT∼1.15 is obtained at 723K, which is 20 times higher than the ZT of un-doped material.

Environmental control of marine phytoplankton stoichiometry in the North Atlantic Ocean

The stoichiometric coupling of carbon to limiting nutrients in marine phytoplankton regulates the magnitude of biological carbon sequestration in the ocean. While clear links between plankton C:N ratios and environmental drivers have been identified, the nature and direction of these links, as well as their underlying physiological and ecological controls, remain uncertain. We show, with a well-constrained mechanistic model of plankton ecophysiology, that while nitrogen availability and temperature emerge as the main drivers of phytoplankton C:N stoichiometry in the North Atlantic, the biological mechanisms involved vary depending on the spatiotemporal scale and region considered. We find that phytoplankton C:N stoichiometry is overall controlled by nitrogen availability below 40° N, predominantly driven by ecoevolutionary shifts in the functional composition of the phytoplankton communities, while phytoplankton stoichiometric plasticity in response to dropping temperatures and increased grazing pressure dominates at higher latitudes. Our findings highlight the potential of "organisms-to-ecosystems" modeling approaches based on mechanistic models of plankton biology accounting for physiology, ecology, and trait evolution to explore and explain complex observational data and ultimately improve the predictions of global ocean models.