Substitution Of Oxygen Research Articles

Factors affecting the properties of highly conductive flexible ultrathin ITO films in confined large area magnetron sputtering in three dimensions

A large area magnetron source with the strongly confined magnetic field from all direction is applied for the deposition of flexible ultrathin ITO (UT-ITO) films of thickness 30 nm at room temperature for their applications as transparent electrodes. The films show a minimum resistivity of ∼5.0 x 10-4 Ωcm and high transmittance >80% at wavelengths of 400-700 nm. Measurements and data reveal that a high plasma density, high energy flux, and a relatively low concentration of negative oxygen ions (NOIs) to the flux of positive ions (PIs) induce lower mechanical stress to the growing films, which enables a lower resistivity and superior crystallinity with the smooth surface. The capability of the magnetron source and the characteristic plasma properties are studied in light of the resulting film properties. The considerably lower resistivity with higher carrier concentration and mobility of the UT-ITO films prepared at a high power density of 3 W/cm2 and a low O2 gas flow can be attributed to the growth of crystallized UT-ITO films, resulting in the combination of the oxygen vacancy and substitution of Sn4+ to In3+ site through the deposition of a high energy flux and a low flux ratio of NOIs to PIs.

New Insight into the Chloroacetanilide Herbicide Degradation Mechanism through a Nucleophilic Attack of Hydrogen Sulfide.

The nucleophilic attack of hydrogen sulfide (HS−) on six different chloroacetanilide herbicides was evaluated theoretically using the dispersion-corrected hybrid functional wB97XD and the 6-311++G(2d,2p) Pople basis sets. The six evaluated substrates were propachlor (A), alachlor (B), metolachlor (C), tioacetanilide (D), β-anilide (E), and methylene (F). Three possible mechanisms were considered: (a) bimolecular nucleophilic substitution (SN2) reaction mechanism, (b) oxygen assistance, and (c) nitrogen assistance. Mechanisms based on O- and N-assistance were discarded due to a very high activation barrier in comparison with the corresponding SN2 mechanism, with the exception of compound F. The N-assistance mechanism for compound F had a free activation energy of 23.52 kcal/mol, which was close to the value for the corresponding SN2 mechanism (23.94 kcal/mol), as these two mechanisms could occur in parallel reactions with almost 50% of each one. In compounds A to D, an important electron-withdrawing effect of the C=O and C=S groups was seen, and consequently, the activation free energies in these SN2 reactions were smaller, with a value of approximately 18 kcal/mol. Instead, compounds E and F, which have a CH2 group in the β-position, presented a higher activation free energy (≈22 kcal/mol). Good agreement was found between experimental and theoretical values for all cases, and a reaction force analysis was performed on the intrinsic reaction coordinate profile in order to gain more details about the reaction mechanism. Finally, from the natural bond orbital (NBO) analysis, it was possible to evaluate the electronic reorganization through the reaction pathway where all the transition states were early in nature in the reaction coordinate (δBav < 50%); the transition states corresponding to compounds A to D turned out to be more synchronous than those for compounds E and F.

Spontaneous doping of the basal plane of MoS2 single layers through oxygen substitution under ambient conditions.

The chemical inertness of the defect-free basal plane confers environmental stability to MoS2 single layers, but it also limits their chemical versatility and catalytic activity. The stability of pristine MoS2 basal plane against oxidation under ambient conditions is a widely accepted assumption however, here we report single-atom-level structural investigations that reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS2 single layers during ambient exposure. The use of scanning tunnelling microscopy reveals a slow oxygen-substitution reaction, during which individual sulfur atoms are replaced one by one by oxygen, giving rise to solid-solution-type 2D MoS2-xOx crystals. Oxygen substitution sites present all over the basal plane act as single-atom reaction centres, substantially increasing the catalytic activity of the entire MoS2 basal plane for the electrochemical H2 evolution reaction.

Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode

Fluorine substitution for oxygen in cation-disordered lithium-excess transition metal oxides (Li1+xTM1–xO2) used as lithium-ion cathodes was recently demonstrated to improve the reversibility of the processes taking place on charge and discharge by reducing the amount of oxygen loss on charge and preventing major structural rearrangements at high voltage. Yet, little is understood about how fluorine incorporates the oxide structure and impacts its electrochemical properties. Here, we use a combination of experimental (solid-state nuclear magnetic resonance (NMR) spectroscopy) and theoretical techniques (density functional theory (DFT) calculations and Monte Carlo simulations) to investigate the evolution of the local structure around fluorine and lithium and the oxidation state of redox-active nickel during charge and discharge of the Li1.15Ni0.45Ti0.3Mo0.1O1.85F0.15 (LNF15) cathode. We show that fluorine doping introduces short-range order in as-synthesized LNF15 by incorporating in lithium-rich sites wi...

Photochemical and Photodynamical Properties of Sulfur‐Substituted Nucleic Acid Bases,

Sulfur-substituted nucleobases (a.k.a., thiobases) are among the world's leading prescriptions for chemotherapy and immunosuppression. Long-term treatment with azathioprine, 6-mercaptopurine and 6-thioguanine has been correlated with the photoinduced formation of carcinomas. Establishing an in-depth understanding of the photochemical properties of these prodrugs may provide a route to overcoming these carcinogenic side effects, or, alternatively, a basis for developing effective compounds for targeted phototherapy. In this review, a broad examination is undertaken, surveying the basic photochemical properties and excited-state dynamics of sulfur-substituted analogs of the canonical DNA and RNA nucleobases. A molecular-level understanding of how sulfur substitution so remarkably perturbs the photochemical properties of the nucleobases is presented by combining experimental results with quantum-chemical calculations. Structure-property relationships demonstrate the impact of site-specific sulfur substitution on the photochemical properties, particularly on the population of the reactive triplet state. The value of fundamental photochemical investigations for driving the development of ultraviolet-A chemotherapeutics is showcased. The most promising photodynamic agents identified thus far have been investigated in various carcinoma cell lines and shown to decrease cell proliferation upon exposure to ultraviolet-A radiation. Overarching principles have been elucidated for the impact that sulfur substitution of the carbonyl oxygen has on the photochemical properties of the nucleobases.

Thermodynamical Stability of Plutonium Monoxide with Carbon Substitution

The existence of condensed plutonium monoxide (PuO) has long been controversial, in which carbon element plays a vital role. In this work, we modeled PuO with carbon substitution of oxygen as the special quasirandom structures of NaCl-type plutonium monoxycarbide (PuOxC1–x) and performed first-principles calculations on these models. It is found that PuO could indeed be stabilized by carbon substitution. The amount of carbon element to stabilize PuO is very small if the source of carbon is CO or CO2. If the carbon is contributed by plutonium monocarbide, the range of stable PuOxC1–x agrees well with the experimental result. By analyzing the electronic structures and chemical bonds, we ascribe the stabilization of PuO by carbon substitution to the newly established Pu 5f/6d–C 2p hybridization around the Fermi level, i.e., stronger Pu–C bonds.

Correlation between thermoluminescence emission and phase transitions of tridymite

ABSTRACTTridymite exhibits a complex 400 nm-induced thermoluminescence spectra consisting of five groups of components at (i) 90 and 130°C (due mainly to oxygen vacancies, substitution and interstitial atoms and/or impurities that create localized charge losses), (ii) 200°C (linked to a partial phase transition), (iii) 230°C (associated probably with alkali ions moving away from Al that leads to [AlO4]° hole-like or [GeO4/Li]° centers) and (iv) 320°C (caused by both phase transition and electron recombination with the unstable holes trapped at oxygen vacancies next to Al sites). The application of the Tm–Tstop protocol confirms a continuum in the trap structure not only because of the successive shifting of the maxima with the increase of the temperature, but also with the enhancement of the activation energy values that have been assessed by means of the initial rise method.

Effect of oxygen substitution and phase on nickel selenide nanostructures for supercapacitor applications

Electrochemical supercapacitors are the eminent technology for the progress of energy storage devices. The current manuscript deals with the formation of oxygen substituted nickel selenide nanostructures and their use as active electrode material for supercapacitor, expecting an enhanced performance owing to their sheet-like geometry, high specific surface area and porous assembly. In this context, Ni(OH)2 (nickel hydroxide) nanostructures were synthesized employing one-pot hydrothermal method and the ion-exchange reaction of Ni(OH)2 nanostructures with selenium resulted in cubic-NiSe2 (nickel selenide) nanostructures. Further, annealing NiSe2 nanostructures at intermediate pressure (10^-3 Torr) has realized the partial oxygen substitution in place of selenium, resulting in NiSe/NiO nanostructures along with phase change from cubic-NiSe2 to hexagonal-NiSe. Supercapacitor electrodes fabricated using NiSe/NiO nanostructures delivered the specific capacitance of 83.5 F g−1 at the scan rate of 2 mV s−1, which is surprisingly more than a double as compared with pristine NiSe2 electrodes (37.4 F g−1). Annealing at intermediate pressure and high temperature significantly enhanced the specific capacitances of the nanostructured electrodes and also accompanied with the good capacitance retention of 94% for 5000 CV cycles.

First-principles study of the nanotubes from the TiO2 hexagonal sheet

Using the method based on the density functional theory, the geometric and electronic properties of the TiO2 single-wall nanotubes, constructed by rolling the most stable nanosheet along the (n, 0) and (n, n) directions, have been investigated systematically. The nanotubes with size from n = 6 up to n = 20 have been modeled and studied. The strain energies of the nanotubes decrease monotonically as the radii of the nanotubes increase, regardless of the rolling direction. The band gaps of the nanotubes are increasing with the increase of the n value, approaching the value of the nanosheet. However, there is one nanotube significantly different from the others, i.e., the (6, 0) nanotube. The substantial structural change of (6, 0) nanotube causes a reduction of the band gap. Then, the isovalent sulfur (S) substitution and adsorption with the (6, 0) nanotube have been studied. Energetically, S adsorption at the inner surface is preferred. Electronically, the band gaps are further reduced by 35% for S substitution of oxygen and 22% for S adsorption, respectively, making the nanotube visible light-sensitive.

Frontiers of Chemical Space

In a recent paper in Energy & Environmental Science, Gerbrand Ceder and colleagues outline a general strategy to design for high transition metal capacity in disordered rocksalt lithium ion cathodes, without reliance on cobalt. Guided by deep consideration of the fundamental limitations of well-studied cathode materials, as well as recent discoveries of Li-percolation in disordered rocksalts and fluorine substitution for oxygen, the authors propose, synthesize, and demonstrate a new high-energy-density cathode material based on both manganese (Mn2+/4+) and vanadium (V4+/5+) redox couples.

A New Strategy for High‐Voltage Cathodes for K‐Ion Batteries: Stoichiometric KVPO4F

AbstractThe exploration of high‐energy‐density cathode materials is vital to the practical use of K‐ion batteries. Layered K‐metal oxides have too high a voltage slope due to their large K+–K+ interaction, resulting in low specific capacity and average voltage. In contrast, the 3D arrangement of K+, with polyanions separating them, reduces the strength of the effective K+‐K+ repulsion, which in turn increases specific capacity and voltage. Here, stoichiometric KVPO4F for use as a high‐energy‐density K‐ion cathode is developed. The KVPO4F cathode delivers a reversible capacity of ≈105 mAh g−1 with an average voltage of ≈4.3 V (vs K/K+), resulting in a gravimetric energy density of ≈450 Wh kg−1. During electrochemical cycling, the KxVPO4F cathode goes through various intermediate phases at x = 0.75, 0.625, and 0.5 upon K extraction and reinsertion, as determined by ex situ X‐ray diffraction characterization and ab initio calculations. This work further explains the role of oxygen substitution in KVPO4+xF1−x: the oxygenation of KVPO4F leads to an anion‐disordered structure which prevents the formation of K+/vacancy orderings without electrochemical plateaus and hence to a smoother voltage profile.

Incorporation of sulfur ions into La2−xSrxCuO4 superconducting cuprate

ABSTRACTThe superconductivity of La2CuO4-based materials is known to be achievable by doping holes in Cu ions. In this study, the hole content was tuned by mixing anion sites with oxygen and sulfur. The substitution of La1.7Sr0.3CuO4 with sulfur led to the recovery of superconductivity from overdoped regions, a result indicative of decreased hole content. Precise structural analysis revealed that the majority of sulfur is incorporated into impurities in the SrSO4 phase, which decreases the hole content of Cu ions via a decrease in the Sr content; however, the superconductivity cannot be interpreted by this mechanism alone. Supporting evidence for the incorporation of sulfur into the La1.7Sr0.3CuO4Sx phase was obtained by an investigation of the composition dependence of the lattice parameters and X-ray photoelectron spectroscopy. Substitution of oxygen with sulfur, which served to decrease the hole content, as a means of recovering superconductivity was shown to act.

Tuning morphology and conductivity in two-step synthesis of zinc-cobalt oxide and sulfide hybrid nanoclusters as highly-performed electrodes for hybrid supercapacitors

We reported a facile two-step hydrothermal procedure to prepare zinc-cobalt oxide and sulfide hybrid nanoclusters (ZCOSH NCs), initialized by the synthesis of metal oxides and followed by the partial substitution of oxygen with sulfur. Benefiting from their morphological features and partial substitution with sulfur, both the electrical conductivity and further the actual specific capacitance of ZCOSH NCs were apparently improved compared to zinc-cobalt binary oxide nanosheets (ZCO NSs). Moreover, its cycling stability has also been significantly enhanced. Its excellent specific capacitance achieved 2176.7 F g−1 at 1 A g−1, which was six times larger than ZCO NSs (367.2 F g−1 at 1 A g−1). Moreover, a hybrid supercapacitor was assembled using ZCOSH NCs as its positive electrode and the activated carbon as its negative electrode. This hybrid supercapacitor device presented a higher specific capacitance value of 116.3 F g−1 at 1 A g−1 with corresponding specific energy of 41.4 W h kg−1 at a specific power of 801.3 W kg−1, and a superior cycling stability after 3000 charge-discharge cycling tests. This study confirmed the feasible and unique synthesis approach to balance the higher capacitance of oxides and the higher electric conductivity of sulfides within this binary ZCOSH NC.

Site-Specific Photodecomposition in Conjugated Energetic Materials.

Nonadiabatic excited-state molecular dynamics (NEXMD) has been used to study photodecomposition in a class of recently synthesized bicyclic conjugated energetic materials (CEMs) composed of fused tetrazole and tetrazine derivatives with increasing oxygen substitutions. Modification by oxygen functionalization has already been demonstrated to increase the two-photon absorption intensity in the target CEMswhile simultaneously improving oxygen balance. Photodecomposition mechanisms in materials that undergo nonlinear absorption could be used to achieve controlled, direct optical initiation. Here, we use NEXMD simulations to model the nonradiative relaxation and photodecomposition in CEMs following photoexcitation by a simulated Nd:YAG laser pulse. Excess electronic energy is quickly converted into vibrational energy on a sub-100 fs time scale resulting in bond dissociation. We find that, for the studiedtetrazine derivatives, the bicyclic framework is an important structural feature that enhances the photochemical quantum yield and the high atomic oxygen content increases the relaxation lifetime and opens additional photodissociation pathways targeting the oxygen-substituted sites. The presented analysis scheme based on bond orders in the swarm of NEXMD trajectories is a useful tool for determining photochemical reactions.

Broadband White-Light Emission from Alumina Nitride Bulk Single Crystals

Alumina nitride bulk single crystals (AlN BSCs) were grown using a two-heater Physical Vapor Transport (th-PVT) method. The crystal contains massive lattice defects including aluminum vacancy (VAl) and oxygen substitution (ON). The photoluminescence (PL) spectrum of the crystal demonstrated a broad emission covering from 250 to 1000 nm. By study the PL spectrum, abundant midgap states in the wide band gap of AlN were nailed down. Based on the crystals, metal-AlN-metal Schottky devices were fabricated. These devices emitted high quality white light with color rendering index (CRI) over 90 under a bias of 60 V. Moreover, it was found that the white light emitting property of AlN BSCs was adjustable through changing impurity density and device structure. This research aims to pave a new way for solid-state white light source.

Peculiar phase diagram with isolated superconducting regions in ThFeAsN1−xOx

ThFeAsN1−xOx () system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the Tc value decreases rapidly to below 2 K for , and surprisingly, superconductivity re-appears in the range of with a maximum of 17.5 K at x = 0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x = 0.4 is , which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN1−xOx presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

Aggregation of modified hexabenzocoronenes as models for early stage asphaltene self-assembly

Molecular dynamics simulations were performed on solvated systems containing three molecules of hexabenzocoronene (HBC) derivatives to model the initial self-association of asphaltenes. Specifically, the hexane-modified HBC (HBC6) and those with substitutions containing a side chain with sulphur at three positions (α-H6SA, β-H6SB, and γ-HBCS) and a nitrogen substitution (H6N1) are included. These molecules were solvated with 20 mol% heptane and 80% toluene. Intermediate aggregation states, partial (two molecule clusters), as well as full aggregation of trimer clusters were observed. The conformation of the associated clusters was characterised by π–π stacking, giving the cluster a pre-rod-like shape. The aggregates displayed stability and did not dissociate throughout the course of the simulation (100–530 ns). In particular, the H6SB system showed statistically significant difference in means for both the separation distance and overall interaction energy. H6N1 and H6SA systems differed from the others in terms of electrostatic contributions. To gain a thorough understanding of initial aggregation behaviour and conditions of asphaltenes, additional simulations need to be conducted, in particular those incorporating oxygen substitutions as oxygen is a common heteroatom in crude.

Pyro-Refining of Mechanically Treated Waste Printed Circuit Boards in a DC Arc-Furnace

This paper presents the results of theoretical assessment and a preliminary experimental investigation of the modified pyrometallurgical processing of metallic granulate obtained after mechanical treatment of waste printed circuit boards (WPCBs). The studied two-step process included oxidation of metallic granulate followed by pyrometallurgical refining in a DC arc-furnace. In the investigated process, the oxygen bounded in metal oxides, obtained during the oxidation annealing of granulate, was used as a “solid” oxidizer for subsequent pyrometallurgical refining in a DC arc-furnace. According to the obtained results, the Cu content in the produced metallic phase (anodic copper) was 98.4% and is suitable for further electro-refining process. In addition, over 94% of Au was concentrated in metallic phase, suggesting that a high Au yield could be attained. However, owing to the distribution between slag phase and filter product, only 60% of Ag was collected in the metal phase. In-between metal and slag is the metal-oxide phase, containing Cu with metals impurities, such as Sn and Pb, which was obtained as well, and could be further treated using conventional processes for additional metal valorization. The investigated concept would allow substitution of the long-lasting oxygen blowing process and application of complicated pyrometallurgical reactors and create a feasible alternative for lower operating capacities.

Ceramic and transport properties of halogen-substituted strontium ferrite

An attempt of fluorine and chlorine substitution for oxygen in strontium ferrite SrFeO3–δ was undertaken in search of a new means of influence on the oxide properties. An uncontrollable removal of halogen-ions from oxides during synthesis was detected. Nevertheless, residual halogens were found to provide a notable impact on ion conductivity and oxide stability under reducing conditions. More than twice higher ion conductivity relative to SrFeO3–δ was recorded in materials with nominal compositions SrFeO2.8–δF0.2, SrFeO2.6–δCl0.4, and SrFeO2.4–δCl0.6. The strong effect of halogen addition on ceramic properties of oxides was revealed. While SrFeO3–δ was known for its poor sinterability, adding 0.2 mol of fluorine or chlorine during the synthesis of SrFeO3–δ was shown to result in successful obtaining gas-tight ceramics.

Structure and ionic conductivity of nitrated lithium disilicate (LiSiON) glasses

Lithium disilicate is a critical glass forming composition as it is the basis of some glass-ceramics and it is also a model glass for the study of homogeneous and heterogeneous crystal nucleation. Incorporation of nitrogen in this glass significantly changes its structure and affects different properties. In this paper, nitrided lithium disilicate glasses were prepared by partial substitution of oxygen up to 6 atm % N/(N + O). The modification of the silicate glass structure with nitrogen has been confirmed by Fourier transform infrared reflection (FTIR) spectroscopy. 29Si NMR and 7Li NMR have also been used to investigate the structural changes due to nitrogen incorporation. Substitution of oxygen by nitrogen with a higher coordination number (three) increases the connectivity of the glass. In fact, our NMR results indicate that nitrogen incorporation changes the Qn distribution (n = average number of bridging oxygens to silicon) of the silicate structural units: SiNO3, SiN2O2 and SiN3O, whereas there is no detectable change in the Li environment. We measured the ionic (Li+) conductivity by impedance spectroscopy and found that the incorporation of nitrogen leads to a decrease in the activation energy for conduction, resulting in an increase of up to four-fold in the ionic conductivity of the most nitrided glass. We explained this high conductivity by the Anderson and Stuart model. This work provides renewed interest in improving and understanding the ionic conductivity in oxynitride glasses.