Positions Of Oxygen Atoms Research Articles

Structure and Properties of the α-Cs2Mo2−xWxO7 Solid Solution

The tungsten substitution for molybdenum in cesium dimolybdate Cs2Mo2O7 with the formation of an α-Cs2Mo2−xWxO7 solid solution is studied, and its homogeneity region at 540 °C is found to reach 0 ≤ x ≤ 0.6. It is established that the volume of the monoclinic (pseudo-orthorhombic) unit cell and the solid solution melting point monotonically increase with increasing tungsten content, whereas the phase transition temperature to the orthorhombic phase remains practically constant and is ∼390 °C. The crystals of solid solutions with several compositions are obtained, their structure is determined, and the tungsten atoms are found to be mainly located in octahedral positions of the α-Cs2Mo2O7 structure. As a result of the phase transition at 390 °C the electrical conductivity of Cs2Mo2O7 increases approximately by two orders of magnitude reaching 1.2·10−4S/cm at 460 °C. Due to a large size of Cs+ ions and a high charge of molybdenum cations it is supposed that the charge carriers are oxygen anions. The calculation of bond valence sum (BVS) maps for possible positions of oxygen atoms in the α-Cs2Mo2O7 cell shows the formation of a 3D system of oxygen conductivity channels at boundary BVS isosurface values ≥ 2.13.

The crystal structure of cubic C-type samarium sesquioxide, Sm2O3

Abstract Cubic C-type samarium sesquioxide, Sm2O3, was prepared by thermal decomposition of samarium carbonate. Its crystal structure was refined based on neutron powder diffraction data [space group Ia3̅, a = 1092.77(6) pm] in order to accurately determine the oxygen atom positions. Isotopically enriched 154Sm2O3 was used for the neutron diffraction work because of the enormous absorption cross section of the natural isotopic mixtures for thermal neutrons. Crystal structure refinements by the Rietveld technique confirm the cubic bixbyite type and yield structure data of high accuracy. Interatomic distances between Sm1 (Wyckoff site 8a) and oxygen are 6 × 235.0(2) pm, and between Sm2 (Wyckoff site 24d) and oxygen 2 × 231.6(2) pm, 2 × 233.7(2) pm, 2 × 240.2(2) pm with a weighted average of d̅(Sm–O) = 235.1(2) pm.

Квантово-химическое моделирование водородных связей в α-глицине

Quantum chemistry was used to simulate a fragment of α-glycine crystal consisting of 5 and 6 glycine molecules. The α-glycine crystal fragment model was constructed using X-ray diffraction data contained in the Cambridge Crystallographic Database (CCDC). Theoretical IR spectra were obtained. It was shown that in a fragment of a crystal, glycine molecules in zwitterionic form form N-H...O hydrogen bonds of different strength, which correspond to different frequencies of stretching vibrations νst (N-H) of the NH3+ group. Full optimization of glycine crystal fragments consisting of a small number of molecules, regardless of the method of calculation, leads to the agglomeration of the structure. The system forms the maximum possible number of the most durable hydrogen bonds, thereby lowering the overall energy of the system, which leads to disruption of the crystal structure of the fragment, distortion of the parameters of hydrogen bonds in the crystal, and, consequently, to an unsystematic shift in the frequencies of N-H vibrations. To avoid this process, further modeling was performed by partially optimizing the geometry of the crystal fragment, with the positions of heavy nitrogen atoms, carbon and oxygen atoms being fixed, and only the positions of hydrogen atoms involved in the formation of hydrogen bonds were varied. Using the DFT/B3LYP/6-311G** method, the energies of donor–acceptor interaction in a fragment of a crystal, as well as its oscillation frequencies, are calculated. The calculated frequencies are consistent with the three experimental frequencies in the indicated X-ray region. A comparison was made between the calculated and experimental frequencies of the stretching vibrations of the N-H group of the NH3+ group. According to the geometric characteristics of the HB and the energy of donor-acceptor interaction between the lone electron pairs of oxygen atoms and the *(N-H) loosening orbitals, it was found that the hydrogen bonds of N-H...O between molecules in one layer are stronger than between molecules in different layers of a crystal.

Five-Membered Cyclic Sulfur Compounds as (Co-)Solvents for Lithium-Ion Battery Electrolytes

Lithium-ion batteries (LIBs) are known for their domination in the market for rechargeable energy storage systems. However, the state-of-the-art non-aqueous aprotic electrolytes, as inevitable components thereof, generally comprising organic carbonates such as ethylene carbonate (EC) and dimethyl carbonate (DMC) with lithium hexafluorophosphate (LiPF6) as conducting salt, still cope with well-known drawbacks and limitations1. In order to realize a substantial improvement, it is of significant importance to tailor new electrolyte formulations and to understand the structural impacts of the electrolyte components, especially solvents, on the electrolyte’s properties. The established organic carbonates, e.g., EC or propylene carbonate (PC), have a structural similarity to five-membered cyclic sulfur compounds. A variation of the oxygen atom number and position leads to five commercially available modifications with constant geometry, i.e., tetrahydrothiophene, tetrahydrothiophene 1-oxide, ethylene sulfite, sulfolane, 1,3-propane sultone and 1, 3, 2- dioxathiolane 2, 2- dioxide. Most of them have already been approved as solid electrolyte interphase (SEI) additives, whereas sulfolane has been used as single or co-solvent, as well2, 3. To reveal the impact of the aforementioned compounds on physicochemical and electrochemical properties of the formulated electrolytes, they were investigated as co-solvents with PC to achieve dissolution of every compound, as 1,3-propane sultone and 1, 3, 2- dioxathiolane 2, 2- dioxide are solid at room temperature. Lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) was used as conducting salt due to its good solubility, thermal and electrochemical stability, and inertness to water4. Viscosity, conductivity, permittivity, Raman and pulsed-field gradient nuclear magnetic resonance (PFG NMR) measurements as well as linear sweep voltammetry (LSV) were conducted to characterize the performance of the formulated electrolytes. It was demonstrated that not the amount of oxygen atoms but the type of functional group (sulfinyl or sulfonyl) plays a decisive role in ionic mobility. Tetrahydrothiophene 1-oxide was selected as promising solvent candidate due to its excellent physicochemical properties. Therefore, the focus for further electrochemical, analytical and spectral characterization was set on this sulfur compound containing electrolytes. The convincing physicochemical properties have a direct impact on the electrochemical behavior, enabling stable galvanostatic cycling of cells containing the PC-based electrolyte. With this in line, interfacial electrochemistry regarding formation, dynamics and also stability of the protective layer was considered, as well. The obtained results pointed out that tetrahydrothiophene 1-oxide as co-solvent in organic carbonate-based electrolytes has a highly positive effect on its ionic mobility as well as on the overall cell performance. S. Hess, M. Wohlfahrt-Mehrens and M. Wachtler, J. Electrochem. Soc., 2015, 162, A3084-A3097.A. Hofmann, M. Schulz, S. Indris, R. Heinzmann and T. Hanemann, Electrochim. Acta, 2014, 147, 704-711.A. Birrozzi, N. Laszczynski, M. Hekmatfar, J. von Zamory, G. A. Giffin and S. Passerini, J. Power Sources, 2016, 325, 525-533.K. Xu, Chem. Rev., 2004, 104, 4303-4417.

Structural defects in LiMn2O4 induced by gamma radiation and its influence on the Jahn-Teller effect

The influence of Jahn-Teller (JT) distortion on the electrochemical behavior of LiMn2O4 is not fully understood nowadays. This paper concerns the role that structural defects play in reducing the magnitude of JT distortion. Structural defects were induced in micrometric and nanometric LiMn2O4 using 60Co gamma radiation. Techniques such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and magic angle spinning spectroscopy (7Li MAS NMR) were used to detect and investigate the defects created by 60Co gamma irradiation in micrometric and nanometric LiMn2O4. Differential scanning calorimetry (DSC) was used to study the effect on the JT distortion enthalpy. Spectroscopic and microstructural modifications of LiMn2O4 produced by the action of radiation are shown for the first time. The results revealed that partial and total edge dislocations are generated after the oxides are irradiated. In the formed dislocations, manganese and lithium ions modified their surroundings and coordination, while the atomic positions of oxygen atoms changed in the fcc structure. These modifications gave rise to a decrease in the magnitude of JT distortion in the micrometric oxides, while no distortion was detected in the nanometric oxides. Because of the defects in LiMn2O4 caused by 60Co gamma irradiation, a minor distortion in the cell parameter (c/a) should be expected when this material is used as a cathode in lithium-ion batteries.

Hybrid classical/quantum simulation for infrared spectroscopy of water

We have developed a hybrid classical/quantum simulation method to calculate the infrared (IR) spectrum of water. The proposed method achieves much higher accuracy than conventional classical molecular dynamics (MD) simulations at a much lower computational cost than ab initio MD simulations. The IR spectrum of water is obtained as an ensemble average of the eigenvalues of the dynamical matrix constructed by ab initio calculations, using the positions of oxygen atoms that constitute water molecules obtained from the classical MD simulation. The calculated IR spectrum is in excellent agreement with the experimental IR spectrum.

Correlation between Geometrically Induced Oxygen Octahedral Tilts and Multiferroic Behaviors in BiFeO3 Films

AbstractThe equilibrium position of atoms in a unit cell is directly connected to crystal functionalities, e.g., ferroelectricity, ferromagnetism, and piezoelectricity. The artificial tuning of the energy landscape can involve repositioning atoms as well as manipulating the functionalities of perovskites (ABO3), which are good model systems to test this legacy. Mechanical energy from external sources accommodating various clamping substrates is utilized to perturb the energy state of perovskite materials fabricated on the substrates and consequently change their functionalities; however, this approach yields undesired complex behaviors of perovskite crystals, such as lattice distortion, displacement of B atoms, and/or tilting of oxygen octahedra. Owing to complimentary collaborations between experimental and theoretical studies, the effects of both lattice distortion and displacement of B atoms are well understood so far, which leaves us a simple question: Can we exclusively control the positions of oxygen atoms in perovskites for functionality manipulation? Here the artificial manipulation of oxygen octahedral tilt angles within multiferroic BiFeO3 thin films using strong oxygen octahedral coupling with bottom SrRuO3 layers is reported, which opens up new possibilities of oxygen octahedral engineering.

Determination of interstitial oxygen atom position in U2N3+xOy by near edge structure study

The determination of interstitial oxygen atom site in U2N3+xOy film could facilitate the understanding of the oxidation mechanism of α-U2N3 and the effect of U2N3+xOy on anti-oxidation. By comparing the similarities and variances between N K edge and O K edge electron energy loss spectra (EELS) for oxidized α-U2N3 and UO2, the present work looks at the local structure of nitrogen and oxygen atoms in U2N3+xOy film, identifying the most possible position of interstitial O atom.

Atomic structure of a metal-supported two-dimensional germania film

Author(s): Lewandowski, AL; Schlexer, P; Buchner, C; Davis, EM; Burrall, H; Burson, KM; Schneider, WD; Heyde, M; Pacchioni, G; Freund, HJ | Abstract: The growth and microscopic characterization of two-dimensional germania films is presented. Germanium oxide monolayer films were grown on Ru(0001) by physical vapor deposition and subsequent annealing in oxygen. We obtain a comprehensive image of the germania film structure by combining intensity-voltage low-energy electron diffraction (I/V-LEED) and ab initio density functional theory (DFT) analysis with atomic-resolution scanning tunneling microscopy (STM) imaging. For benchmarking purposes, the bare Ru(0001) substrate and the (2×2)3O covered Ru(0001) were analyzed with I/V-LEED with respect to previous reports. STM topographic images of the germania film reveal a hexagonal network where the oxygen and germanium atom positions appear in different imaging contrasts. For quantitative LEED, the best agreement has been achieved with DFT structures where the germanium atoms are located preferentially on the top and fcc hollow sites of the Ru(0001) substrate. Moreover, in these atomically flat germania films, local site geometries, i.e., tetrahedral building blocks, ring structures, and domain boundaries, have been identified, indicating possible pathways towards two-dimensional amorphous networks.

Первопринципные термодинамические характеристики образования кислородных вакансий и примесных центров бора, углерода и азота в анатазе

AbstractUsing the ab initio projector augmented wave (PAW) method, calculations are performed for the electronic energy-band structure of titanium dioxide having the structure of anatase doped with boron, nitrogen, and carbon. Thermodynamic characteristics are determined for the formation of impurity centers, such as the preference energy for the interstitial position, the energy of impurity oxidation, and the energy of oxygen vacancy formation. It is shown that under the conditions of thermodynamic equilibrium the interstitial position of boron atoms is stable, whereas carbon atoms, depending on the oxygen pressure, can occupy both interstitial positions and substitutional positions of oxygen atoms, and nitrogen atoms replace oxygen atoms. It is shown that the presence of oxygen vacancies promotes the thermodynamic stability of carbon and nitrogen atoms. The obtained densities of electronic states correspond to ESR spectroscopy data, which indicates the presence of spin-polarized electrons in the states of the oxygen vacancy.

Ab initio thermodynamic characteristics of the formation of oxygen vacancies, and boron, carbon, and nitrogen impurity centers in anatase

Using the ab initio projector augmented wave (PAW) method, calculations are performed for the electronic energy-band structure of titanium dioxide having the structure of anatase doped with boron, nitrogen, and carbon. Thermodynamic characteristics are determined for the formation of impurity centers, such as the preference energy for the interstitial position, the energy of impurity oxidation, and the energy of oxygen vacancy formation. It is shown that under the conditions of thermodynamic equilibrium the interstitial position of boron atoms is stable, whereas carbon atoms, depending on the oxygen pressure, can occupy both interstitial positions and substitutional positions of oxygen atoms, and nitrogen atoms replace oxygen atoms. It is shown that the presence of oxygen vacancies promotes the thermodynamic stability of carbon and nitrogen atoms. The obtained densities of electronic states correspond to ESR spectroscopy data, which indicates the presence of spin-polarized electrons in the states of the oxygen vacancy.

The structural, electronic and spectroscopic properties of 4FPBAPE molecule: Experimental and theoretical study

The experimental and theoretical study of 4-Formyl Phenyl Boronic Acid Pinacol Ester (4FPBAPE) molecule were performed in this work. 1H, 13C NMR and UV–Vis spectra were tested in dimethyl sulfoxide (DMSO). The structural, spectroscopic properties and energies of 4FPBAPE were obtained for two potential conformers from density functional theory (DFT) with B3LYP/6-311G (d, p) and CAM-B3LYP/6-311G (d, p) basis sets. The optimal geometry of those structures was obtained according to the position of oxygen atom upon determining the scan coordinates for each conformation. The most stable conformer was found as the A2 form. The fundamental vibrations were determined based on optimized structure in terms of total energy distribution. Electronic properties such as oscillator strength, wavelength, excitation energy, HOMO, LUMO and molecular electrostatic potential and structural properties such as radial distribution functions (RDF) and probability density depending on coordination number are presented. Theoretical results of 4-FPBAPE spectra were found to be compatible with observed spectra.

Ab initio modeling of transport and thermodynamic stability for hafnia memristive devices

HfO $$_2$$ -based memristive switching devices are currently under intensive investigation due to their high performance and mature fabrication techniques. However, several critical issues have to be addressed to bring them from laboratory to market. We have recently looked into two important issues with the use of density functional theory methods. One is the wide distribution of device resistance in off-states. We have modeled the switching process of a Pt–HfO $$_2$$ –Pt structure for which quantized conductance was observed. Oxygen atoms moving inside a conductive oxygen vacancy filament divide the filament into several quantum wells. Device conductance changes exponentially when one oxygen atom moves away from interface into filament. We propose that the high sensitivity of device conductance to the position of oxygen atoms results in the large variation of device off-state resistance. Another issue that we have recently addressed is the poor switching performance of devices based on a TiN–HfO $$_2$$ –TiN structure. While recent experiments have shown that by inserting an “oxygen scavenger” metal between positive electrode and oxide significantly improves device performance, the fundamental understanding of the improvement is lacking. We provide detailed understanding how scavenger layers improve device performance. First, we show that Ta insertion facilitates the formation of on-states by reducing the formation energy. Second, the inserted Ta layer reduces the Schottky barrier height in the off-states by changing interface electric dipole at the oxide/electrode interface. Nevertheless, the device maintains a high on/off-resistance ratio. Finally, with Ta insertion the on-state conductance becomes much less sensitive to the specific location from which the oxygen was removed from the oxide. Our studies provide fundamental understanding needed for enabling realization of a nonvolatile memory technology with reduced energy consumption.

(Invited) Conductivity and Dielectric Relaxations in New Morpholinium- and Piperidinium-Based Ionic Liquids

Room Temperature Ionic Liquids (RTILs) are key materials for the development of new energy storage and conversion systems [1]. In the past decade several relevant properties such as their negligible vapour pressure, non-flammability, and high room-temperature conductivity were explored in order to obtain safer and better performing devices [2]. Despite of this, the complex interplay existing between the IL nanostructure and the conductivity mechanism is still under discussion within the scientific community [3]. Following this, the synthesis of new ILs and the investigation of their electrical properties are of crucial importance and could pave the way to new applications in the field of ion-conducting materials [4, 5]. This contribution summarizes the electrical study of a family of ILs based on 1-methylmorpholinium (MM+) and 1-methylpiperidinium (MP+) cations. The MM+ and MP+ cations have been synthesized comprising two different alkyl side chain substituents on the nitrogen atom, namely 1-methoxyethyl (ME) and 1-ethoxyethyl (EE) groups. A set of four cations (ME-MM+, EE-MM+, ME-MP+ and EE-MP+) neutralized by TFSI-anions is obtained, thus giving rise to four new RTILs. The structure of these ILs allows the systematic investigation of the presence of oxygen atoms on the aliphatic ring (see morpholinium vs. piperidinium cations) with respect to the different substituent side chain length (see methoxyethyl vs.ethoxyethyl groups). The effect of the oxygen atom position on the diffusion of conformational states as well as the charge transfer mechanism is particularly interesting for future Lithium battery applications in which the oxygen atoms are expected to play a crucial role on the migration of Li cations. At this regard, Broadband Electrical Spectroscopy (BES) measurements were undertaken to elucidate the electrical response of the ILs in terms of dielectric relaxations and polarization phenomena. At T<Tg (Tg=glass transition temperature) dielectric relaxations are present, associated with the rotational motions of morpholinium and piperidinium cations bearing permanent dipole moment; at T>Tg, interdomain polarization events are detected. These polarization events are associated with the presence of cation and anion nanocluster aggregates with different permittivities. The results allow us to correlate the dielectric relaxations of the different cations with the overall long-range charge migration, thus elucidating the interplay existing between conductivity and nanostructure of this new ILs.

Insights into Photosystem II from Isomorphous Difference Fourier Maps of Femtosecond X-ray Diffraction Data and Quantum Mechanics/Molecular Mechanics Structural Models.

Understanding structure–function relations in photosystem II (PSII) is important for the development of biomimetic photocatalytic systems. X-ray crystallography, computational modeling, and spectroscopy have played central roles in elucidating the structure and function of PSII. Recent breakthroughs in femtosecond X-ray crystallography offer the possibility of collecting diffraction data from the X-ray free electron laser (XFEL) before radiation damage of the sample, thereby overcoming the main challenge of conventional X-ray diffraction methods. However, the interpretation of XFEL data from PSII intermediates is challenging because of the issues regarding data-processing, uncertainty on the precise positions of light oxygen atoms next to heavy metal centers, and different kinetics of the S-state transition in microcrystals compared to solution. Here, we summarize recent advances and outstanding challenges in PSII structure–function determination with emphasis on the implementation of quantum mechanics/molecular mechanics techniques combined with isomorphous difference Fourier maps, direct methods, and high-resolution spectroscopy.

Синтез и строение комплекса родия [trans-Na∙18-crown-6∙(dmso-O)2]+ [trans-RhBr4(dmso-S)2

Шарутин Владимир Викторович – доктор химических наук, профессор, старший научный сотрудник УНИД, Южно-Уральский государственный университет. 454080, г. Челябинск, пр. им. В.И. Ленина, 76. E-mail: vvsharutin@rambler.ru. Шарутина Ольга Константиновна – доктор химических наук, профессор, кафедра теоретической и прикладной химии, Южно-Уральский государственный университет. 454080, г. Челябинск, пр. им. В.И. Ленина, 76. E-mail: sharutinao@mail.ru. Сенчурин Владислав Станиславович – кандидат химических наук, доцент, кафедра теоретической и прикладной химии, Южно-Уральский государственный университет. 454080, г. Челябинск, пр. им. В.И. Ленина, 76. E-mail: senvl@rambler.ru Сонникова Екатерина Сергеевна – студент, химический факультет, Южно-Уральский государственный университет. 454080, г. Челябинск, пр. им. В.И. Ленина, 76. E-mail: katerina_sonnikova@mail.ru V.V. Sharutin, vvsharutin@rambler.ru O.K. Sharutina, sharutinao@mail.ru V.S. Senchurin, senvl@rambler.ru E.S. Sonnikova, katerina_sonnikova@mail.ru South Ural State University, Chelyabinsk, Russian Federation

The crystal structure of mineral fibres: 1. Chrysotile

This work reports the result s of the structural study of three representative chrysotile samples of different provenance (Canadian UICC, and Italian Balangero and Valmalenco) . Chemical composition was determined using EMPA and TG data. An innovative wet cryo-milling procedure was used to powder the resistant-to-abrasion chrysotile fibres. X-ray powder diffraction patterns were collected using both conventional and non-conventional sources. Collected data were used for Rietveld structural refinements and results were compared with available literature data. The three samples display similar structure models, although small differences were detected in the position of the oxygen atoms. Both the structural refinements and spectroscopic investigations confirms that Fe 2+ and Fe 3+ atoms in chrysotile are located in the octahedral cavities only, substituting for Mg 2+ . Regarding the atom coordinates, UICC chrysotile is the more similar to the model reported by Falini et al. (2004). About the lattice parameters, the Valmalenco chrysotile is the more similar, if compared with the Balangero and UICC, to both the model proposed by Whittaker (1956a,b) and Falini et al. (2004) . This work is intended as a basis for subsequent studies aimed at understanding the potential toxicity of these mineral fibres.

Oxygen-modulated quantum conductance for ultrathin HfO2 -based memristive switching devices

Memristive switching devices, candidates for resistive random access memory technology, have been shown to switch off through a progression of states with quantized conductance and subsequent non-integer conductance (in terms of conductance quantum $G_0$). We have performed calculations based on density functional theory to model the switching process for a Pt-HfO$_2$-Pt structure, involving the movement of one or two oxygen atoms. Oxygen atoms moving within a conductive oxygen vacancy filament act as tunneling barriers, and partition the filament into weakly coupled quantum wells. We show that the low-bias conductance decreases exponentially when one oxygen atom moves away from interface. Our results demonstrate the high sensitivity of the device conductance to the position of oxygen atoms.

On the role of spatial position of bridged oxygen atoms as surface passivants on the ground-state gap and photo-absorption spectrum of silicon nano-crystals

Silicon nano-crystals (NCs) are potential candidates for enhancing and tuning optical properties of silicon for optoelectronic and photo-voltaic applications. Due to the high surface-to-volume ratio, however, optical properties of NC result from the interplay of quantum confinement and surface effects. In this work, we show that both the spatial position of surface terminants and their relative positions have strong effects on NC properties as well. This is accomplished by investigating the ground-state HOMO-LUMO band-gap, the photo-absorption spectra, and the localization and overlap of HOMO and LUMO orbital densities for prototype ∼1.2 nm Si32–xH42–2xOx hydrogenated silicon NC with bridged oxygen atoms as surface terminations. It is demonstrated that the surface passivation geometry significantly alters the localization center and thus the overlap of frontier molecular orbitals, which correspondingly modifies the electronic and optical properties of NC.

Magnetic and transport properties assisted by local distortions in Bi2Mn4O10 and Bi2Fe4O9 multiferroic compounds

We have performed a comprehensive study on the magnetic and electrical properties through macroscopic and local characterizations on Bi2Mn4O10 and Bi2Fe4O9. An analysis of the temperature evolution of local distortions, which was obtained by perturbed angular correlation measurements, revealed an anomalous behavior of the quadrupolar frequency and asymmetry parameter below the antiferromagnetic ordering temperature for both samples. The combined results suggest correlations between magnetic, electric, and elastic interactions. At high temperature, we have observed that the hopping frequency and activation energy in the electrical transport mechanism are close related to hyperfine parameters, electrical field gradient and asymmetry parameter, due to modifications in the equilibrium positions of oxygen atoms conforming octahedral, pyramidal, and tetrahedral environments. Anharmonic lattice effects are much more pronounced in a temperature range close to room temperature.