O2 Bonds Research Articles

(Ni1/3Nb2/3)4+-Improved High-K Ba3Ti4Nb4O21 Microwave Dielectric Ceramics for Miniaturized All-Ceramic Radomes with 5G Beam-Splitting Function.

With the rapid development of 5G communication technology, microwave dielectric ceramics with high dielectric constants are very conducive to the miniaturization of passive devices. Here, Ba3Ti4-x(Ni1/3Nb2/3)xNb4O21 (BTN ∼ NN, 0.03 ≤ x ≤ 0.15) ceramics with hexagonal phases are synthesized via the solid-phase route. The composite (Ni1/3Nb2/3)4+ ion substitution strategy can substantially improve the microwave dielectric properties of the Ba3Ti4Nb4O21 (BTN) ceramic. The εr and Q × f values depend on the ionicity (Nb-O bonds) and lattice energies (Nb(1)-O3 and Nb(1)-O2(1) bonds). The microwave dielectric properties of the BTN ∼ NN (x = 0.09) ceramic sintered at 1250 °C are εr = 60.3, Q × f = 22073 GHz, and τf = 78.1 ppm/°C. A miniaturized all-ceramic radome (@400 mm × 400 mm × 8 mm) for 5G beam-splitting function is designed and demonstrated using this ceramic. Compared to other radomes designed for other work utilizing low εr, the size of this radome has been reduced by 3/7. The reflection coefficients of the beam splitting function are all 0.73, and the phase shifts are all 360°. This work contributes to the development of miniaturized passive devices from a materials point of view.

Insights into the Fe3+ Doping Effects on the Structure and Electron Distribution of Cr2O3 Nanoparticles.

Herein, we carefully investigated the Fe3+ doping effects on the structure and electron distribution of Cr2O3 nanoparticles using X-ray diffraction analysis (XRD), maximum entropy method (MEM), and density functional theory (DFT) calculations. We showed that increasing the Fe doping induces an enlargement in the axial ratio of c/a, which is associated with an anisotropic expansion of the unit cell. We found that as Fe3+ replaces Cr in the Cr2O3 lattice, it caused a higher interaction between the metal 3d states and the oxygen 2p states, which led to a slight increase in the Cr/Fe-O1 bond length followed by an opposite effect for the Cr/Fe-O2 bonds. Our results also suggest that the excitations characterize a well-localized bandgap region from occupied Cr d to unoccupied Fe d states. The Cr2O3 and Fe-doped Cr2O3 nanoparticles behave as Mott-Hubbard insulators due to their band gap being in the d-d gap, and Cr 3d orbitals dominate the conduction band. These findings suggest that the magnitude and the character of the electronic density near the O atom bonds in Cr2O3 nanoparticles are modulated by the Cr-Cr distances until its stabilization at the induced quasi-equilibrium of the Cr2O3 lattice when the Fe3+ doping values reaches the saturation level range.

Phase transition and bond symmetrization associated with noble gas bond in XeO3

The pressure-induced structural phase transition of XeO3 is studied by first principle calculations. The transition from P212121 to Pnma accompanied by a drastic reduction of volume is found at 2.18 GPa. The symmetrilized Xe−O2 bonds give rise to the better symmetry of high pressure phase. O-hopping between different possible local minima and the motion of Xe along the y axis may be responsible for phase transition. Results of electron localization function indicate that three ipsilateral Xe−O bonds lead to a lone-pair contour of Xe6+.

Structural, spectroscopic, luminescence and magnetic properties of a novel far-red emitting phosphor Er, Mn doped ZrTe3O8

Polycrystalline ZrTe3O8:2%Er, 3%Mn was prepared by the solid-state reaction technique. The formation of single-phase material was determined by X-ray diffraction studies and found to be a cubic phase at room temperature. The structure can be described by two types of polyhedrons, namely disphonoids (TeO4E with E = electronic lone pair of Te4+) and octahedrons of ZrO6. The bridges Te-O1-Te and Te-O2-Zr ensured the crystal structure cohesion. Both kinds of polyhedron oxygen were coordinated along the [0 1 0] mixed chain, linked to a pure chain of tellurium through O1 in order to form a two-dimensional network and then a unit cell with a three-dimensional network. The Raman spectrum was dominated by a strong band at 841 cm-1corresponding to Te-O2-Zr bridges asymmetric stretching vibration. Consequently, the Te-O2 and Zr (Mn)O2 bonds are chemically inequivalent and the ZrO2Te bridges are chemically asymmetric. The magnetic results reveal the appearance of a weak ferromagnetic behavior at low temperature.The emission properties of the ZrTe3O8:2%Er, 3%Mn prepared at relatively high temperature examined at 490 nm excitation led to an appearance of an important emission in the visible and near-infrared domains due to homogeneously occupied Er3+ ions in the host lattice. Therefore, this kind of phosphors may be a meaningful reference for W-LEDs application.

The Origin of the Chiral gauche-Conformation Preferences in Halomethyl Methyl Ethers. A Hybrid-Density Functional Study and Natural Bond Orbital Interpretation

The effects of the stereoelectronic interaction on the structural and conformational properties of fluoromethyl methyl ether (1) and its analogues containing Cl (2), Br (3), and I (4) atoms were investigated by means of hybrid-density functional based method (B3LYP/Def2-TZVPP) and natural bond orbital (NBO) interpretation. Consistent with the reported experimental data, the chiral gauche conformations of compounds 1–4 are more stable than their corresponding anti conformations. The results showed that the energy barriers of the racemization processes of the chiral gauche-conformations of compounds 1–4 via the plane symmetrical anti conformations are smaller than the plane symmetrical eclipsed transition structures. According to the NBO analysis, the hyperconjugative generalized anomeric effect (HCGAE) increased from compound 1 to compound 4, which explains the increase of the energy discrepancy between their corresponding chiral gauche- and plane symmetrical anti-conformations. In contrast to the trend for the HCGAE, the determined dipole moment discrepancy between the chiral gauche- and plane symmetrical anti-conformations (µanti–µgauche) reduced from compound 1 to compound 4. This fact reveals that there is no correlation between the variations of the conformational preferences in compounds 1–4 and the electrostatic effects associated with the dipole–dipole interactions. There is an excellent agreement between the racemization energy barriers and the proportion between the GAE for compounds 2–4 and compound 1 (i.e., GAEx/GAE1) as well as the difference between the Wiberg Bond Indexes of C1–O2 bonds (Δ[WBIanti-gauche(C1–O2)]). The associations between the HCGAE, pairwise steric exchange energies (PSEE), WBI, dipole moments, orbital integrals, structural parameters, and conformational behaviors of compounds 1–4 have been studied.

The Role of the Fe/Mo Cations Ordering Degree and Oxygen Non‐Stoichiometry on the Formation of the Crystalline and Magnetic Structure of Sr2FeMoO6−δ

Single‐phase Sr2FeMoO6−δ powders with various oxygen indices (δ) and degrees of the superstructural ordering (P) of the Fe/Mo cations are obtained from SrFeO2.52 and SrMoO4 reagents via solid‐state synthesis. It has been established by means of the X‐ray and neutron diffraction that, upon reducing the oxygen content and enhancing the superstructural ordering, the lengths of the Fe–O1 and Mo–O2 bonds in the crystal lattice increase, whereas the Fe–O2 and Mo–O1 bond lengths decrease. At the same time, the volume of the unit cell is reduced, which indicates an enhancement of the covalency degree of the bonds and stimulates a redistribution of the electron density, as well as an increase of the concentration of the spin‐down charge carriers located in the conduction band on the Mo(t2g)↓ orbitals. This circumstance leads to an increase of the density of states at the Fermi level, accompanied by an amplification of the exchange interaction and elevation of the Curie temperature, which points to the leading role of the spin‐polarized charge carriers at the Fermi level in the exchange interaction.

Modeling the Self-Assembly of 5-Hydroxy-6-methyluracil within Electrostatic Potential Approach

The sites of reactions in 5-hydroxy-6-methyluracil (HMU) and its dimeric and tetrameric associates are studied theoretically in terms of the electrostatic potential (ESP). The ESP approach allows us to construct the most stable combinations of HMU associates and to study HMU self-assembly without simulating all possible associates. A self-assembly scheme is proposed for HMU. N1–H···O1 bonds initially form between the molecules. If the first recognition center (RC) is occupied, N3–H···O2 bonds form with the participation of the third RC. The resulting ribbons with alternating contacts 1–1 and 3–3 are cross-linked through the electrostatic attraction of hydroxyl groups and the forces of dispersion between methyl groups.

O2 adsorbed on Ptn clusters: Structure and optical absorption

The interaction of O2 with Ptn and the optical absorption properties of PtnO2 were explored under the framework of density functional theory. The Ptn (n= 2, 4, 6, 9, 10, 14, 18, 22, and 27) clusters were selected, which were reported as magnetic number Ptn clusters in reference (V. Kumar and Y. Kawazoe, Phys. Rev. B 77(20), 205418 (2008)). The single Pt atom was also considered. The longest O2 bonds were found for Pt27O2, Pt6O2 and Pt14O2, while PtO2 and Pt2O2 have the shortest O2 bonds. This result showed that the single Pt atom was not preferred for O2 activation. The O2 bond length was closely related to the electron transfer from Ptn to O2. The optical absorptions of PtnO2 were investigated with time-dependent density functional theory method. A new term of charge transfer strength was defined to estimate the further electron transfer from Ptn to O2 caused by the optical absorption in the visible light range. Our calculations showed that with the increasing n, the further electron transfer from Ptn to O2 caused by optical absorption will become very weak.

Crystal structures of (E)-2-((2-((pyridin-2-yl)hydrazonyl)methyl)phenolic compounds: different sets of classical hydrogen bonds, X–H···Y (X, Y = O, N)

Abstract Structures are reported of (E)-((2-((pyridin-2-yl)hydrazonyl)methyl)arene compounds, 2-aryl-CH=N–CH)-pyridine, 8, namely (aryl=2,4-(HO)2C6H3, 8a; 2,5-(HO)2C6H3, 8b, 2–HOC6H4, 8c, as the hemihydrate, [(8c) 2· (H 2 O )], 2–HO–5–O2NC6H3, 8d; and 2,6-(MeO)2C6H3, 8e. Intramolecular O1–H1··· N2(hydrazonyl) hydrogen bonds are consistantly found in each of the hydroxy compounds, 8a–8d. However, a diverse array of classical intermolecular hydrogen bonds, X–H···Y (X or Y = O or N) are found in 8a–8e. Classical intermolecular hydrogen bonds in 8a are chain forming N3–HN3···O1 and O2–H2···N1(pyridinyl) intermolecular hydrogen bonds, while in the isomer, 8b, dimer forming N3–HN3···N1(pyridinyl) and chain forming O2–H2···O1(pyridinyl) hydrogen bonds are present. The hydrate molecule in [(8c) 2 ·(H 2 O)] is involved in Ow–Hw···N1 intermolecular hydrogen bonding: also present in [(8c) 2 ·(H 2 O)] are chain forming N3–HN3···O2 bonds. The only intermolecular classical hydrogen bonds present in 8d and 8e, are the dimer forming N3–HN3···N1(pyridinyl) bonds. Thus only compounds, 8b, 8d and 8e, exhibit dimer forming N3–HN3···N1(pyridinyl) hydrogen bonds, previously reported fora range of (aryl-CH=N–CH)-pyridine derivatives. The occurence of N3–HN3···N1(pyridinyl) hydrogen bonds in many (aryl-CH=N–CH)-pyridine derivatives demonstrates the importance of such hydrogen bonds. However, as found in 8a and [(8c) 2 ·( H 2 O )], suitable sited donor substituents or the presence of solvate molecules can result in other classical hydrogen bonds being preferred.

Role of Pr cations and the low temperature transition in Pr0.50Sr0.50CoO3: A comparison to Pr0.50Ca0.50CoO3

The low temperature properties of Pr0.50Sr0.50CoO3 are studied in comparison to Pr0.50Ca0.50CoO3, which is known to exhibit a Pr3+/Pr4+ valence shift below TMI~80K. The evolution of the Pr–O network strongly differs in the Sr and Ca compounds, but both have in common a prominent and sudden contraction of some Pr–O bonds. The structural phase transition that accompanies the so-called magnetocrystalline anisotropy transition at TS~120K in Pr0.50Sr0.50CoO3 brings about a notable contraction of some Pr–O2 bonds. The observations give support to the active participation of Pr-4f electrons at the intriguing magnetostructural transition (TS) in Pr0.50Sr0.50CoO3. In addition, we have confirmed that (in absence of praseodymium) the magnetostructural transition is suppressed in (Nd2/3La1/3)0.50Sr0.50CoO3, a perovskite with the same average cationic size at the A-site than Pr0.50Sr0.50CoO3.

Crystal structure and magnetic properties of CuSb2O4

The crystal structure of a copper antimonite (CuSb2O4) was determined from X-ray powder diffraction data. The structure was solved by simulated annealing in direct space using the Rietveld method. The compound crystallizes in tetragonal symmetry and space group P4 2 bc (106); unit cell parameters a = b = 8.76033(5) Å, c = 5.79786(4) Å, Z = 4, V = 444.947(5) Å3 and density (calc.) = 5.539 g cm−3. The CuO6 polyhedra are strongly elongated due to Jahn–Teller distortion in a [2+2+2] coordination arrangement, i.e. there are two long axial Cu–O1 bonds of 2.447(13) Å and in the equatorial plane there are two intermediate Cu–O2 bonds of 2.07(3) Å and two short Cu–O2 bonds of 1.88(2) Å. The SbO3 pyramidal arrangement is almost regular with Sb–O1 bonds of 1.97(2) Å (2×) and Sb–O2 of 1.959(5) Å. The experimentally obtained Raman spectrum is consistent with values obtained from theoretical modelling studies. The magnetic behaviour of this new compound suggests that it belongs to the class of S = 1/2 Heisenberg chain systems.

Nuclear and charge density distributions in ferroelectric PbTiO3: maximum entropy method analysis of neutron and X-ray diffraction data

We conducted in-situ high-temperature neutron and X-ray diffraction studies on tetragonal PbTiO3. Using a combination of Rietveld analysis and Maximum Entropy Method, the nuclear and charge density distributions were determined as a function of temperature up to 460 °C. The ionic states obtained from charge density distributions reveal that the covalency of Pb–O2 bonds gradually weakens with increasing temperature. The spontaneous polarizations calculated from the contributions of ionic state, ionic displacement, and nuclear polarization, are in good agreement with the experimental measurements. This method provides an effective approach to determine spontaneous polarizations in multiferroics with high-current leakage and low resistance.

A Density Functional Theory Study of Formaldehyde Adsorption on CeO2(111) Surface

采用基于第一性原理的密度泛函理论和周期平板模型,研究了甲醛在以桥氧为端面的CeO2（111）稳定表面上的吸附行为.通过对不同覆盖度,不同吸附位的甲醛吸附构型、吸附能及电子态密度的分析发现,甲醛在CeO2（111）表面存在化学吸附与物理吸附两种情况.化学吸附结构中甲醛的碳、氧原子分别与表面的氧、铈原子发生相互作用,形成CH2O2物种;吸附能随着覆盖度的增加而减小.与自由甲醛分子相比,物理吸附的甲醛构型变化不大,其吸附能较小.利用CNEB（climbing nudged elastic band）方法计算了甲醛在CeO2（111）表面的初步解离反应活化能（约1.71eV）,远高于甲醛脱附能垒,这与甲醛在清洁CeO2（111）表面程序升温脱附实验中产物主要为甲醛的结果相一致.

Ab-initio calculations of the proton location in topaz-OH, Al 2 SiO 4 (OH) 2

The position of hydrogen in the structure of topaz-OH was determined by means of ab-initio quantum-mechanic calculations. Static lattice energy calculations predict the existence of four non-equivalent positions of protons, which are characterized by O4–H1... O1, O4–H2... O2, O4–H3... O3 and O4–H4... O4 hydrogen bonds. The distribution of the protons between positions of local equilibrium is controlled by the proton–proton avoidance rule and the strength of the hydrogen bonds. The most favourable configuration of hydrogen atoms is achieved for adjacent protons, which form O4–H3... O3 and O4–H4... O4 hydrogen bonds, respectively. The thermal excitation of atoms at a temperature of 55 K is large enough for the hydrogen atoms occasionally to change their positions to form O4–H1... O1 and O4–H2... O2 bonds. At ambient pressures and higher temperatures the protons are in a dynamic exchange between the allowed positions of local minima. As a consequence, for nearly room-temperature conditions, the dynamic change between different structural configurations leads to the violation of all possible symmetry elements and with that to space group #E5/E5#1. The flipping of the protons between different sites is achieved by simple rotation of the OH-dipole and does not produce any significant distortion of the framework of topaz, whose symmetry remains that of the space group Pbnm. Therefore, no reduction of symmetry has been observed in former X-ray studies on topaz-OH. Calculated IR absorption spectra of topaz-OH were found to be in good agreement with measured spectra. According to the calculations, the two favourable configurations of protons might correspond to the measured peak splitting within the OH-stretching range. An experimentally observed low-frequency band at 3520 cm−1 was assigned to the OH-stretching of the O4–H3... O3 bond, while the band at 3600 cm−1 was attributed to OH-stretching of the O4–H4... O4 hydrogen bond. The broad peak in FAR-IR frequency range at 100–150 cm−1 is attributed to the stretching of H3... O3 and H4... O4 contacts. The rate of proton exchange at 670 K among different sites was estimated by ab-inito molecular dynamic simulations. The calculations predict that flipping of adjacent protons between O4–H3... O3 and O4–H4... O4 bonds at 670 K occur at a rate of about 1.96 THz.

Regioselectivity in the reductive ring-opening reaction of 1,2- O-benzylidene sugars

Regioselectivity in the ring-opening reaction of 1,2- O-benzylidene sugars was studied. In the reductive ring-opening reaction of 1,2- O-benzylidene derivatives, only a C O1 bond was cleaved in the case of manno-type, but both the C O1 and C O2 bonds were cleaved in the case of gluco-type.

Crystal engineering in the gem-alkynol family: the key role of water in the structure of 2,3,5,6-tetrabromo-trans-1,4-diethynyl-cyclohexa-2,5-diene-1,4-diol dihydrate determined by X-ray and neutron diffraction at 150 K.

The structure of the title compound has been determined using low-temperature (150 K) single-crystal X-ray and neutron diffraction data. Crystals adopt the uncommon space group P4(2)/ncm and display a complex set of intermolecular interactions in which the water molecules play the crucial role: the water O-atom [O2(w)] accepts two hydrogen bonds and both water H atoms act as bifurcated donors. A set of O--H...O hydrogen bonds is formed around the 4(2) axis comprising (a) a cyclic tetrameric synthon involving four donor-H from two water molecules and two O(hydroxy) acceptors from two parent molecules, and (b) short discrete O(hydroxy)--H...O2(w) hydrogen bonds which link these tetramers along the c axis. Four Br...Br interactions [3.708 (1) A] form cyclic Br(4) tetramers around the 4 axis and are linked to the O--H...O system via O2(w)--H...Br bonds with H...Br = 2.995 (2) A. Finally, the O--H...O system is further linked to the parent molecules via C identical with C...H...O2(w) bonds of 2.354 (3) A. The supramolecular structure of the title hydrate is compared with that of the non-hydrated parent molecule, which also forms cyclic O--H...O bonded tetrameric synthons, and with its (non-hydrated) tetrachloro analogue, which forms cyclic tetrameric Cl(4) synthons [Madhavi, Desiraju et al. (2000b). Acta Cryst. B56, 1063--1070].

Determinants of the FeXO (X = C, N, O) Vibrational Frequencies in Heme Adducts from Experiment and Density Functional Theory

Vibrational spectra of CO, NO, and O2 adducts of heme proteins contain information on interactions of the heme and its bound ligands with the surrounding protein matrix that may help in elucidating the mechanism of small-molecule activation. Whereas the heme−CO system is well studied and a framework exists for the interpretation of such interactions, heme−NO and −O2 complexes have not been systematically investigated. Here we examine resonance Raman spectra of all three classes of adducts, combining literature values with new data for FeIINO porphyrins having both electron-donating and electron-withdrawing substituents. Negative linear correlations are observed for all three adducts between their Fe−XO and X−O stretching frequencies. The slopes of these correlation lines are −0.4 for five-coordinate FeCO and FeNO porphyrins and −0.8 for five-coordinate FeO2 adducts. Thus, Fe−NO and Fe−O2 bonds are equally or even more sensitive than Fe−CO bonds to electronic influences that affect metal-to-ligand π back-b...

A comparative study of O2, CO, and NO binding to iron-porphyrin

Minimum-energy structures of O2, CO, and NO iron–porphyrin (FeP) complexes, computed with the Car–Parrinello molecular dynamics, agree well with the available experimental data for synthetic heme models. The diatomic molecule induces a 0.3–0.4 Å displacement of the Fe atom out of the porphyrin nitrogen (Np) plane and a doming of the overall porphyrin ring. The energy of the iron–diatomic bond increases in the order Fe(SINGLE BOND)O2 (9 kcal/mol) < Fe(SINGLE BOND)CO (26 kcal/mol) < Fe(SINGLE BOND)NO (35 kcal/mol). The presence of an imidazole axial ligand increases the strength of the Fe(SINGLE BOND)O2 and Fe(SINGLE BOND)CO bonds (15 and 35 kcal/mol, respectively), with few structural changes with respect to the FeP(CO) and FeP(O2) complexes. In contrast, the imidazole ligand does not affect the energy of the Fe(SINGLE BOND)NO bond, but induces significant structural changes with respect to the FeP(NO) complex. Similar variations in the iron–imidazole bond with respect to the addition of CO, O2, and NO are also discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 31–35, 1998

Polarized X-Ray Absorption Fine Structure of La2CuO4-ySingle Crystal

Polarized Cu K X-ray absorption fine structure (XAFS) has been measured on a single crystal of undoped La 2 CuO 4- y for the first time, using a fluorescence detection technique. The polarized near-edge structure and EXAFS were strongly anisotropic, demonstrating the quasi-two-dimensional nature of electron states and local structure. The polarization dependence of the near-edge structure confirms that the Cu atoms take 2+ valence or d 9 configuration with a strong fourfold Cu–O1 bonds within the CuO 2 plane and weak twofold Cu–O2 bonds along the c -axis, which is consistent with the anisotropic local structure suggested by the Fourier transform of polarized EXAFS and a crystal structure.

Infrared and Raman spectra of the new superconducting cuprate perovskites MBa 2Cu 3O 7, M =Nd, Dy, Er, Tm

We report far-infrared and Raman studies of several ceramic superconducting cuprate perovskites MBa 2Cu 3O 7 with M=Nd, Dy, Er, Tm. Systematic studies of the phonon-related peaks show that the frequencies of optical phonons related to vibrations of M atoms decrease slightly with increasing atomic number of the rare earth, thus confirming the trend observed earlier for M=Y, Sm, Eu, Gd, Ho. The temperature dependence of phonon features exhibits an anomalous behavior for the optical phonons at ∼310 cm −1 and 280 cm −1. Such anomalous temperature dependence of phonons attributed to the bond bending vibrations of Cu2O2 and Cu2O3 bonds, seems to be a universal property of all superconducting cuprates. Possible origins of the phonons softening and the systematics of the variation of phonon frequencies with the ionic radius of M are discussed.