Role Of Stoichiometry Research Articles

Decoupled response of microbial taxa and functions to nutrients: The role of stoichiometry in plantations

The resource quantity and elemental stoichiometry play pivotal roles in shaping belowground biodiversity. However, a significant knowledge gap remains regarding the influence of different plant communities established through monoculture plantations on soil fungi and bacteria's taxonomic and functional dynamics. This study aimed to elucidate the mechanisms underlying the regulation and adaptation of microbial communities at the taxonomic and functional levels in response to communities formed over 34 years through monoculture plantations of coniferous species (Japanese larch, Armand pine, and Chinese pine), deciduous forest species (Katsura), and natural shrubland species (Asian hazel and Liaotung oak) in the temperate climate. The taxonomic and functional classifications of fungi and bacteria were examined for the mineral topsoil (0–10 cm) using MiSeq-sequencing and annotation tools of microorganisms (FAPROTAX and Funguild). Soil bacterial (6.52 ± 0.15) and fungal (4.46 ± 0.12) OTUs' diversity and richness (5.83*103±100 and 1.12*103±46.4, respectively) were higher in the Katsura plantation compared to Armand pine and Chinese pine. This difference was attributed to low soil DOC/OP (24) and DON/OP (11) ratios in the Katsura, indicating that phosphorus availability increased microbial community diversity. The Chinese pine plantation exhibited low functional diversity (3.34 ± 0.04) and richness (45.2 ± 0.41) in bacterial and fungal communities (diversity 3.16 ± 0.15 and richness 56.8 ± 3.13), which could be attributed to the high C/N ratio (25) of litter. These findings suggested that ecological stoichiometry, such as of enzyme, litter C/N, soil DOC/DOP, and DON/DOP ratios, was a sign of the decoupling of soil microorganisms at the genetic and functional levels to land restoration by plantations. It was found that the stoichiometric ratios of plant biomass served as indicators of microbial functions, whereas the stoichiometric ratios of available nutrients in soil regulated microbial genetic diversity. Therefore, nutrient stoichiometry could serve as a strong predictor of microbial diversity and composition during forest restoration.

Study on the Role of Stoichiometry in Quality Management

In recent years, with the continuous development of the society, people's requirements for product quality are getting higher and higher. Enterprises pay more and more attention to the quality management work, and take the corresponding quality management measures, established the quality management system. It is found that the current stoichiometry technology plays an important role in quality management, and the product quality has been significantly improved. Therefore, the author deeply thinks and analyzes the influence of stoichiometry on product quality and its role in quality management, and studies how to optimize the application of stoichiometry technology in quality management, in order to open up ideas for improving the efficiency of quality management.

Hydrothermal Synthesis of Perovskite CsPbBr3: Spotlight on the Role of Stoichiometry in Phase Formation Mechanism

Hydrothermal Synthesis of Perovskite CsPbBr3: Spotlight on the Role of Stoichiometry in Phase Formation Mechanism

Comparative measurements and analysis of the mechanical and electrical properties of Ti-Zr-C nanocomposite: Role of stoichiometry

Nanocomposites based on hard compounds are currently on the stage of active research and development. Hence the analysis of a relation between nanostructure and functional properties are of great importance. The main purpose of the study was to assess the stoichiometry effect on the finite characteristics of TiZrC nanocomposite coatings. This paper presents the analysis of the Ti1-xZrxC (x = 0, 0.25, 0.5, 0.75 and 1.0) hard coatings sputtered onto Si substrates by a two-target DC magnetron. It has been found that the increase of carbon content in the bulk of the coatings contributes to the structural changes, namely, lead to the formation of the nc-Ti1-xZrxCy/a-C nanocomposite structure with (Ti,Zr)C solid-solution phase which is in a good agreement to theoretical predictions. Electrical properties measurements have shown infrequent results concerning intrinsic conductivity, which can prosper this system application for a new generation of nano and microsystems. The analysis reveals the nature of tunnelling conductance between the nanoparticles. On the computer simulation of the frequency dependence of the frequency coefficient, three maxima were discovered. Two of them were attributed to dominant phases (Ti1-xZrx)C and amorphous carbon (a-C). The third one is related to the content of another type of nanophase that, due to low content, could not be determined by structural methods. Mechanical tests showed promising results in suitability to micromechanical devices, in particular: sensors, actuators, power-producing devices. These findings establish an understanding of microstructural regularities and enlarge the potential application space for TiZrC-based systems.

Green Synthesis of High Quantum Yield Carbon Dots from Phenylalanine and Citric Acid: Role of Stoichiometry and Nitrogen Doping

Despite a growing interest in carbon dots (CDs), notably for their potential as a more sustainable, less toxic alternative to inorganic quantum dots, the critical factors affecting their physical, ...

Exsolution and electrochemistry in perovskite solid oxide fuel cell anodes: Role of stoichiometry in Sr(Ti,Fe,Ni)O3

The exsolution of metal cations from oxides under reducing fuel conditions results in the formation of surface metallic nanoparticles, which can reduce Solid Oxide Fuel Cell anode polarization resistance. However, the loss of the B-site cations shifts the stoichiometry of the perovskite oxide. Depending on the amount exsolved and the initial stoichiometry, the exsolution can presumably shift the oxide away from its single-phase perovskite region. Herein, the direct comparison of initially stoichiometric composition Sr(Ti0.3Fe0.63Ni0.07)O3-δ (STFN0) with initially A-site deficient Sr0.95(Ti0.3Fe0.63Ni0.07)O3-δ (STFN5) is conducted and reported. X-ray diffraction along with scanning and transmission electron microscopy analysis of the oxides, which are both reduced at 850 °C in H2/H2O/Ar, shows a similar size and density of exsolved Fe–Ni alloy nanoparticles, albeit with slightly different alloy compositions. Whereas the oxide phase in reduced STFN5 shows a well-ordered perovskite structure, the greater B-site deficiency in reduced STFN0 results in a highly disordered and strained structure. The electrochemical performance of STFN0 anodes is inferior to that of STFN5 anodes, and even worse than SrTi0.3Fe0.7O3-δ (Ni-free) anodes. It appears that an initial Sr deficiency is important to avoid a too-high B-site deficiency after exsolution, which distorts the perovskite structure and impairs electrochemical processes.

Influence of Charge Transport Layers on Open-Circuit Voltage and Hysteresis in Perovskite Solar Cells

Summary Perovskite materials have experienced an impressive improvement in photovoltaic performance due to their unique combination of optoelectronic properties. Their remarkable progression, facilitated by the use of different device architectures, compositional engineering, and processing methodologies, contrasts with the lack of understanding of the materials properties and interface phenomena. Here we directly target the interplay between the charge-transporting layers (CTLs) and open-circuit potential ( V OC ) in the operation mechanism of the state-of-the-art CH 3 NH 3 PbI 3 solar cells. Our results suggest that the V OC is controlled by the splitting of quasi-Fermi levels and recombination inside the perovskite, rather than being governed by any internal electric field established by the difference in the CTL work functions. In addition, we provide novel insights into the hysteretic origin in perovskite solar cells, identifying the nature of the contacts as a critical factor in defining the charge accumulation at its interface, leading to either ionic, electronic, or mixed ionic-electronic accumulation.

Inverted Hysteresis in CH3NH3PbI3 Solar Cells: Role of Stoichiometry and Band Alignment.

J-V hysteresis in perovskite solar cells is known to be strongly dependent on many factors ranging from the cell structure to the preparation methods. Here we uncover one likely reason for such sensitivity by linking the stoichiometry in pure CH3NH3PbI3 (MAPbI3) perovskite cells with the character of their hysteresis behavior through the influence of internal band offsets. We present evidence indicating that in some cells the ion accumulation occurring at large forward biases causes a temporary and localized increase in recombination at the MAPbI3/TiO2 interface, leading to inverted hysteresis at fast scan rates. Numerical semiconductor models including ion accumulation are used to propose and analyze two possible origins for these localized recombination losses: one based on band bending and the other on an accumulation of ionic charge in the perovskite bulk.

Molecular Beam Epitaxy of lithium niobium oxide multifunctional materials

The role of stoichiometry and growth temperature in the preferential nucleation of material phases in the Li-Nb-O family are explored yielding an empirical growth phase diagram. It is shown that while single parameter variation often produces multi-phase films, combining substrate temperature control with the previously published lithium flux limited growth allows the repeatable growth of high quality single crystalline films of many different oxide phases. Higher temperatures (800–1050°C) than normally used in MBE were necessary to achieve high quality materials. At these temperatures the desorption of surface species is shown to play an important role in film composition. Using this method single phase films of NbO, NbO2, LiNbO2, Li3NbO4, LiNbO3, and LiNb3O8 have been achieved in the same growth system, all on c-plane sapphire. Finally, the future of these films in functional oxide heterostructures is briefly discussed.

The Role of Stoichiometry in Contact Interaction of Zirconia with Metal Melts

As a transition metal compound, zirconia can lose oxygen with the formation of nonstoichiometric phases. The stoichiometry affects the properties of material, therefore, the wetting of nonstoichiometric zirconia with inert metals (Cu, Ni, Sn, Ge, Ag, Pt) and alloys (Cu–Ga, Cu–Ge, Cu–Ni) is studied under conditions when the high oxygen deficit in zirconia is caused by the contact interaction with metal melts (such as Cu–Ti, Ni–Ti, Ti). It is established that the melts of inert metals can wet nonstoichiometric zirconia. This effect is explained as follows: the oxygen deficit may be considered as the zirconium surplus; this surplus of zirconium dissolves in the metal melt and, when the melt composition changes, then, the surface properties of the melt change too. Since zirconium is an active metal, the adhesion of the melt to the oxide substrate increases. In case of nickel, the microstructural study reveals nickel–zirconium intermetallide on the metal–oxide interface indicating the interaction of the nickel melt with zirconium from the substrate. Thermodynamic calculations show that such process is quite possible. Thin films are also considered. It is found out that Pt, Pd, and Ni films on stoichiometric zirconia are congregated in the islands at the temperatures significantly lower than the melting temperatures of corresponding metals, while they remain continuous on nonstoichiometric zirconia. Also, it can be explained by the chemical interaction of the metal film with the substrate.

Ab Initio Calculations of Ionic Conductivity in Lithium and Sodium Polyborate Solid Electrolytes

A subset of alkali polyborates have recently been identified as highly promising solid electrolytes for next-generation batteries due to their superionic transition temperatures approaching room temperature and ionic conductivities exceeding 0.1 S/cm–1. However, the exact mechanisms driving the transport in these materials remain largely unknown. Here we use large-scale ab initio molecular dynamics calculations to characterize the diffusivity of the Li and Na species in a representative set of B12H12- and B10H10-based closoborane ionic conductors, focusing on the role of stoichiometry, volume, and dopant incorporation in enhancing ionic conductivity. Detailed analysis on representative materials is used to elucidate the specific conduction mechanism, which relies on frustrated competition between longer- and shorter-range interionic interactions. Our results support this class of materials as highly promising solid electrolytes and offer insights that can be used to tailor conductivity and stability for their use in next-generation battery technologies. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Interaction of turbulent premixed flames with combustion products: Role of stoichiometry

Stabilization methods of turbulent flames often involve mixing of reactants with hot products of combustion. The stabilizing effect of combustion product enthalpy has been long recognized, but the role played by the chemical composition of the product gases is typically overlooked. We employ a counterflow system to pinpoint the effects of the combustion product stoichiometry on the structure of turbulent premixed flames under conditions of both stable burning and local extinction. To that end, a turbulent jet of lean-to-rich, CH4/O2/N2-premixed reactants at a turbulent Reynolds number of 1050 was opposed to a stream of hot products of combustion that were generated in a preburner. While the combustion product stream temperature was kept constant, its stoichiometry was varied independently from that of the reactant stream, leading to reactant-to-product stratification of relevance to practical combustion systems. The detailed structure of the turbulent flame front was analyzed in two series of experiments using laser-induced fluorescence (LIF): joint CH2O LIF and OH LIF measurements and joint CO LIF and OH LIF measurements. Results revealed that a decrease in local CH2O+OH and CO+OH reaction rates coincide with the depletion of OH radicals in the vicinity of the combustion product stream. These critical combustion reaction rates were more readily quenched in the presence of products of combustion from a stoichiometric flame, whereas they were favored by lean combustion products. As a result, stoichiometric combustion products contributed to a greater occurrence of local extinction. Furthermore, they limited the capacity of premixed reactants to ignite and of the turbulent premixed flames to stabilize. In contrast, lean and rich combustion products facilitated flame ignition and stability and reduced the rate of local extinction. The influence of the combustion product stream on the turbulent flame front was limited to a zone of approximately two millimeters from the gas mixing layer interface (GMLI) of the product stream. Flame fronts that were separated from the GMLI by larger distances were unaffected by the product stream stoichiometry.

The role of stoichiometry in superconducting Nb1-βSnβ: electronic and vibrational properties from ab initio calculations.

Using first principles calculations based on density functional theory, the electronic, vibrational and superconducting properties of compounds with different stoichiometry ratios in the A15 phase have been studied. To this purpose, the λ mass enhancement parameter, which determines the superconducting critical temperature through the Allen-Dynes modification of the McMillan formula, has been explicitly calculated in the context of the density functional perturbation theory that allows the calculation of the matrix elements of the electron-phonon interactions at different compositions related to the Sn content. Our results provide a better understanding of the inhomogeneous composition of one of the most widely employed low-temperature superconductors, evidencing the electronic properties and the phonon modes that are responsible for the critical temperature degradation as the Sn concentration is varied.

Cation stoichiometry and electrical transport properties of the NdGaO3/(0 0 1)SrTiO3 interface

The interface formed between two wide band-gap insulators, NdGaO3 and SrTiO3 renders metallic behavior, similar to the LaAlO3/SrTiO3 interface. The interface conductivity depends strongly upon oxygen pressure during growth of the NdGaO3 film and subsequent annealing in oxygen. The conductivity of a (10 uc) NdGaO3/SrTiO3 film, pulsed laser deposited at low (pO2 = 10−4 mbar) oxygen pressure, vanishes after annealing at 600 °C in oxygen atmosphere. For a similar interface formed at high oxygen pressure (pO2 = 0.3 mbar), the metallic conductivity remains also after post annealing. Medium energy ion spectroscopy (MEIS) in random (non-channeling) direction showed that a substantial part of Ga is missing in films deposited at low pressure, while optimal stoichiometry is approached in films deposited at high pressure. Aligned (channeling) MEIS likewise show that the Ga/Nd ratio approaches the stoichiometric value as the pressure is increased from 10−4 to 0.3 mbar. This is interpreted as due to gallium desorption from a growing film at high temperature and low oxygen pressure while the re-evaporation of gallium is considerably suppressed at higher pressure. We discuss the possible role of stoichiometry on electrical transport properties.

The Roles of Gβγ and Gα in Gating and Regulation of GIRK Channels.

G protein-gated K(+) (GIRK, or Kir3) channels mediate inhibitory neurotransmission via G protein-coupled receptors (GPCRs) in heart and brain. The signaling cascade involves activation of GPCR by an agonist, activation of a G protein followed by rearrangement or dissociation of activated Gα(GTP) from Gβγ, and activation of GIRK by Gβγ. Gβγ is the main transducer of GPCR activating signal to the GIRK channel. It promotes channel opening by direct binding to GIRK's cytosolic domain formed by the N- and C-terminal segments of the GIRK's four subunits. Gβγ's interaction with, and activation of, the GIRK channels are well understood and reviewed elsewhere; however, several important details involving distal parts of the cytosolic domain remain incompletely understood. Gα(i/o) also binds to GIRKs and has been implicated in regulating channel's gating, in concert with Gβγ. Among known functions of Gα, best-described (though not well understood) are selectivity of signaling (only G(i/o) proteins normally couple to GIRKs) and regulation of the basal activity of GIRKs (I(basal)). A role for a direct effect of the activated Gα(i/o)(GTP) in GIRK gating has also been proposed but remains elusive. This chapter discusses the mechanisms of signaling within the essential cascade, from GPCR to the heterotrimeric G protein and to the channel. The focus is on the role of Gα and on the relationships between Gα and Gβγ in channel regulation, their role in specific signaling from GPCRs to GIRKs, and the role of stoichiometry and cooperativity of G protein-GIRK interactions in channel's function.

Role of Stoichiometry on Ordering in Ni-Cr Alloys

ABSTRACTMechanical property degradation due to an ordering phase transformation is a concern for alloys based on the Ni-Cr binary system (e.g., 690, 625), particularly in nuclear power applications, such as stream generator tubing, reactor pressure vessel and head control rod drive mechanism penetrations, where component lifetimes can exceed 40 years. In the present research, the disorder-order phase transformation has been studied in Ni-Cr model alloys with varying stoichiometry by experimental methods. In this paper, the effect of composition on ordering is characterized via X-ray diffraction.

Role of Stoichiometry in the Dimer-Stabilizing Effect of AMPA Receptor Allosteric Modulators

Protein dimerization provides a mechanism for the modulation of cellular signaling events. In α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors, the rapidly desensitizing, activated state has been correlated with a weakly dimeric, glutamate-binding domain conformation. Allosteric modulators can form bridging interactions that stabilize the dimer interface. While most modulators can only bind to one position with a one modulator per dimer ratio, some thiazide-based modulators can bind to the interface in two symmetrical positions with a two modulator per dimer ratio. Based on small-angle X-ray scattering (SAXS) experiments, dimerization curves for the isolated glutamate-binding domain show that a second modulator binding site produces both an increase in positive cooperativity and a decrease in the EC50 for dimerization. Four body binding equilibrium models that incorporate a second dimer-stabilizing ligand were developed to fit the experimental data. The work illustrates why stoichiometry should be an important consideration during the rational design of dimerizing modulators.

The Role of Stoichiometry on Gas Response of Nanostructured Sol–Gel Auto Combustion Derived Nickel Ferrite

The Role of Stoichiometry on Gas Response of Nanostructured Sol–Gel Auto Combustion Derived Nickel Ferrite

Two-Dimensional and Three-Dimensional Coordination Polymers of Hexakis(4-cyanophenyl)[3]radialene: The Role of Stoichiometry and Kinetics

Hexakis(4-cyanophenyl)[3]radialene (1) is a hexadentate ligand that has previously been shown to form isomorphous honeycomb two-dimensional (2-D) coordination polymers {[Ag(1)](X)·2(CH3NO2)}n (X = ClO4, 2a; X = PF6, 2b) upon reaction with AgClO4 and AgPF6. Within these coordination polymers, close contacts were observed between the anions and the electron-deficient [3]radialene core. Here the synthesis and characterization of four new coordination polymers of 1 and copper(I), {[Cu2(1)2](X)2·Y(CH3NO2)}n (X = BF4, Y = 20, 4a; X = PF6, Y = 14, 4b) and {[Cu(1)](X)·2(CH3NO2)}n (X = BF4, 5a; X = PF6, 5b), are reported, along with two further examples of the (6,3) network {[Ag(1)](X)·2(CH3NO2)}n (X = BF4, 2c; X = SbF6, 2d), and an 8-fold interpenetrated (10,3)-b net formed from 1 and AgClO4, {[Ag3(1)](ClO4)3·CH3NO2}n (3). Coordination polymers 2a–2d were synthesized using low ratios of ligand to metal, 1:1 to 1:3, whereas other examples described herein (compounds 3, 4, and 5) were obtained via the use of a cons...

Non-conducting interfaces of LaAlO3/SrTiO3 produced in sputter deposition: The role of stoichiometry

We have investigated the properties of interfaces between LaAlO3 films grown on SrTiO3 substrates singly terminated by TiO2. We used RF sputtering in a high-pressure oxygen atmosphere. The films are smooth, with flat surfaces. Transmission electron microscopy shows sharp and continuous interfaces with some slight intermixing. The elemental ratio of La to Al, measured by the energy dispersive X-ray technique, is found to be 1.07. Importantly, we find these interfaces to be non-conducting, indicating that the sputtered interface is not electronically reconstructed in the way reported for films grown by pulsed laser deposition because of the different interplays among stoichiometry, mixing, and oxygen vacancies.