Structure of ZnZrF<Subscript>6</Subscript> · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (<Emphasis Type="Italic">n</Emphasis> = 6–2) and ZnZrF<Subscript>6</Subscript> crystallohydrates according to vibrational spectroscopy data

Fluoridezirconate crystallohydrates ZnZrF₆ · nH₂O (n = 6–2) and anhydrous ZnZrF₆ are investigated by vibrational spectroscopy and thermography. The influence of the hydrate number on the structure of the cationic and anionic sublattices of the crystallohydrates is studied. The changes in the strength of HOH···F and HOH···O hydrogen bonds of coordinated and outer-sphere water molecules occurring with variations in the hydrate number are determined by changes in the IR spectra. The IR spectra of ZnZrF₆ · nH₂O (n =6, 4) compounds, which have isolated complex anions [ZrF₆]^2– in their structure, revealed a band with two peaks in the range of 3470–3430 cm^–1, which corresponds to stretching vibrations of coordinated water molecules. The spectra of ZnZrF₆ · nH₂O (n = 5, 3, 2, 1) crystallohydrates with a polymeric structure show a high-frequency shift of this band, which corresponds to weakening of hydrogen bonds. The vibrations of crystallization water molecules involved in the network of strong O–H···F and O–H···O hydrogen bonds manifest themselves in the spectra of ZnZrF₆ · nH₂O (n =5, 3) crystallohydrates by broad structureless bands in the region of stretching, bending, and libration vibrations.     

Polarized IR and Raman spectra of (H<Subscript>2</Subscript>O)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters (<Emphasis Type="Italic">n</Emphasis> = 2–5) in the <Emphasis Type="Italic">c</Emphasis>-channels of apatite single crystals

The infrared (IR) and Raman spectra of three samples of fluorapatite single crystals and carbonate fluorapatite single crystal in the region of 7000–400 cm^–1 were studied. It has been shown that isomorphic substitution of the Ca²⁺ cation and the PO₄^3- anion leads to an increase in the size of the c-channels in the apatite crystal, which is accompanied by the formation of water clusters of the (H₂O) _n and H₃O⁺ · (H₂O) _n (n = 2–5) types as a result of the diffusion processes in these local sections of the c-channels.     

H<Subscript>3</Subscript>O<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack> ions with a strong quasi-symmetrical H-bond and their hydration in aqueous solutions of NaOH and KOH

Ion-molecular interactions in aqueous solutions of NaOH (0–47.8%) and KOH (0–51.95%) are studied by multiple frustrated total internal reflection IR spectroscopy. Interpretation of the spectra and analysis of the spectral data are performed based on the results of DFT calculations (B3LYP/6-31++G(d, p)) of the characteristics of the free and double hydrated H₃O ₂ ^- ion. It is established that the changes in the IR spectra of NaOH and KOH aqueous solutions caused by increasing alkali concentration are due to the formation of H₃O ₂ ^- ions with a strong quasi-symmetrical hydrogen bond and their subsequent hydration by one or two water molecules. The influence of the cation nature on the degree of hydration of H₃O ₂ ^- ions is demonstrated. The equilibrium concentrations of monohydrate (H₃O ₂ ^- ? H₂O) and dihydrate (H₃O ₂ ^- ? 2H₂O) are calculated and their IR continuous absorption spectra are isolated.     

The influence of the proton affinity of molecules that form proton disolvates on disolvate hydrogen bridge parameters

The optimum structures of thirty three proton disolvates (B…H…B)⁺ and (B…H…S)⁺ containing O…H⁺…O, N…H⁺…N, and N…H⁺…O hydrogen bridges were calculated by the density functional theory method (B3LYP/6-31++G(d, p)). The bridge parameters are compared with the proton affinities (PAs) of B and S molecules. Several dependences between the PA or ΔPA = PA_B ? PA_S values and the R _OO, R _NN, and R _NO distances were established. It follows from these results that the proton affinity of oxygen-or nitrogen-containing molecules that form (B…H…B)⁺ and (B…H…S)⁺ ions is an important but not the only factor determining the geometric parameters of hydrogen bridges in them. The dependences obtained can be used to estimate the length of the central fragment of proton disolvates if the PA values of molecules in the disolvates are known. They also allow the degree of proton transfer (the R _N…H and R _H…O distances) to be estimated for N…H⁺…O bridges.     

Thermodynamic study of compounds of the Nd-Ba-Cu-O system

Standard enthalpies of formation for solid solutions of composition Nd_{1 + x} Ba_{2 ? x} Cu₃O _y (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa₂Cu₃O_6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy S ^o(T), the difference of enthalpies H ^o(T)-H ^o(0 K), and the reduced Gibbs energy Φ^o(T) = S ^o(T)–[H ^o(T)–H ^o(0)]/T were calculated on the basis of smoothed dependence C _p (T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd_1+x Ba_2?x Cu₃O _y . The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.     

Exchange Bias in Layered GdBaCo<Subscript>2</Subscript>O<Subscript>5.5</Subscript> Cobaltite

It is established that excess oxygen content δ influences the exchange bias (EB) in layered GdBa-Co₂O_{5 + δ} cobaltite. The EB effect arises in p-type (δ > 0.5) cobaltite and disappears in n-type (δ < 0.5) cobaltite. The main parameters of EB in GdBaCo₂O_5.52(2) polycrystals are determined, including the field and temperature dependences of EB field H _EB , blocking temperature T _B , exchange coupling energy J _i of antiferromagnet–ferromagnet (AFM–FM) interface, and dimensions of FM clusters. The training effect inherent in systems with EB has been studied. The results are explained in terms of exchange interaction between the FM and AFM phases. It is assumed that the EB originates from the coexistence of Co³⁺ and Co⁴⁺ ions that leads to the formation of monodomain FM clusters in the AFM matrix of cobaltite.     

<Superscript>16</Superscript>O/<Superscript>18</Superscript>O oxygen isotope exchange kinetics in MnO<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> as probed by <Superscript>55</Superscript>Mn NMR

The effect of the ¹⁶O ? ¹⁸O substitution in the coordination sphere of permanganate anion MnO ₄ ^? on the chemical shift of ⁵⁵Mn nuclei have been studied by ¹⁷O and ⁵⁵Mn NMR. Time constants τ _n,k of oxygen exchange in the water–permanganate anion system have been estimated. In nearly neutral solutions (pH ≈ 6.8–7.2), the oxygen exchange time is on the order of tens of hours. Bubbling gaseous HCl through this solution for a few seconds leads to the equilibrium distribution of oxygen isotopes in the manganese coordination sphere. The observed temperature dependences of isotope-induced ⁵⁵Mn NMR shifts in Mn¹⁶ O _44-n ¹⁸ O _n ^– (n = 0–4) have been treated as a result of rovibrational averaging of Mn–O bond lengths. The change in the Mn—O bond length in caused by the ¹⁶O → ¹⁸O isotope substitution is on the order of 10^–4 Å.     

Löslichkeit,Diffusion und Ultrarotabsorption von Wassermolekülen in Alkalihalogenidkristallen

Following a former communication, further experiments of solubility, diffusion and infraredabsorption of water molecules in KCl-, KBr- and KJ-crystals are given. Substituted mono- and bivalent ions to the refined crystals strongly increase the solubility of water at lower temperatures but there is practically no increase at higher temperatures. This points to two mechanisms for solubility: An interstitial at lower temperatures and probably by vacancies at higher temperatures. — The penetration of water into crystals containing K₂O orF-centers produces a colorless layer by chemical reaction. From investigation of such layers we get diffusion constants for the diffusion of water molecules. In crystals containingF-centers we find an additionalKH- layer. — The chemical reactions in the solid state produce H^?-, OH^?- and O^??-centers of well known concentration. This allows determination of the oscillator strengths of the characteristical ultraviolett absorptions. — The absorption in the near infrared by crystals containing water shows especially at low temperatures sharp peaks from single H₂O-molecules and broad peaks from precipitated water. An interstitial lattice model is discussed for the single H₂O-molecules.     

Spectroscopy of optical centers of Eu<Superscript>3+</Superscript> ions in partially stabilized and stabilized zirconium crystals

The structure of the optical centers of Eu³⁺ ions in tetragonal (ZrO₂)_1–x–y (Y₂O₃) _x (Eu₂O₃) _y (х = 2.7–3.6; y = 0.1) and cubic (ZrO₂)_1–x–y (Y₂O₃) _x (Eu₂O₃) _y (х = 8–38; y = 0.1–0.5) crystals of solid solutions on the basis of zirconium dioxide is studied using the methods of optical and Raman-scattering spectroscopy. Characteristic optical centers of Eu³⁺ ions with different crystalline environments are revealed in the above compounds.     

On the mechanisms of formation of excited hydrogen atoms in a decaying helium-hydrogen plasma

We spectroscopically studied the population of the excited hydrogen atomic states with the principal quantum numbers n=3 and 4 in a decaying plasma produced by a pulsed discharge in a mixture of helium (p=40.4 Torr) with a small amount of hydrogen ([H₂]≈10¹² cm^?3). Experiments on recording the response of the spectral line intensities to a short-duration electron temperature perturbation revealed the contribution of electron-ion recombination to the population of the H*(n=3) states in the early afterglow. The ions produced by collisions of hydrogen molecules with metastable He(2³ S ₁) atoms, whose density decreases relatively rapidly with time in the decaying plasma, were assumed to be involved in this process. No population of the H*(n=4) atomic levels due to electron-ion recombination was found. Our experimental results are consistent with the conclusions of previous studies that excitation transfer during collisions of metastable helium molecules with hydrogen molecules plays a major role in the population of the excited hydrogen atomic states both with n=3 and with n=4 during most of the afterglow.     

EPR study of the spin dynamics of the (La<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>Pr<Subscript>y</Subscript>)<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> system

The EPR of Mn ions in the (La_1?yPr_y)_0.7Ca_0.3MnO₃ system has been studied within a broad range of temperatures (4<T<600 K) and Pr concentrations (0≤y≤1), as well as under isotope substitution of ¹⁸O for ¹⁶O. All compositions were shown to undergo transitions to a magnetically ordered state with decreasing temperature. Magnetic phase diagrams were constructed for systems with different oxygen isotopes. The diagrams include paramagnetic, ferromagnetic, and antiferromagnetic regions. In the paramagnetic region, at temperatures not too close to the phase transition points, the Mn ion linewidth ΔH _pp (T) is related to the magnetic susceptibility χ(T) through the relation ΔH _pp (T) = [χ₀/χ(T)]ΔH _pp (∞) + ΔH₀, where ΔH _pp (∞) is the width of the exchange-narrowed line in the high-temperature approximation, χ₀ ∝ 1/T is the susceptibility of noninteracting ions, and ΔH₀ is the residual width originating from the sample porosity and resonance-field scatter in unoriented grains of a powder sample. An analysis of the data on ΔH _pp (∞), ΔH₀, and χ(T) made it possible to estimate the symmetric and antisymmetric exchange interaction of Mn ions and of the noncubic crystal-field component of the oxygen ions. These parameters were found to be independent of the oxygen isotope species to within experimental error.     

Relativmessung integrierter Wirkungsquerschnitte für den Kernphotoeffekt: Die Reaktion O16(γ, n)O15

Li₂CO₃ and Na₂C₄H₈O₈ have been irradiated by 34 MeV bremsstrahlung. The yield of the induced O¹⁵ activity has been measured relative to the yield of the C¹²(γ, n)C¹¹ resp. Cu⁶³(γ, n)Cu⁶² reaction by detecting the annihilation quanta. Additional yield measurements with the bremsstrahlung beam attenuated by 18 mm of lead were made to determine the ratio of the integrated cross sections for the reactions O¹⁶(γ, n)O¹⁵ and C¹²(γ, n)C¹¹ resp. Cu⁶³(γ, n)Cu⁶². Using the cross section ofBarber et al. for C¹²(γ, n)C¹¹, the cross section integrated up to 33 MeV for O¹⁶(γ, n)O¹⁵ was obtained to 61±7 MeVmb.     

Reactions of initiation of the autoignition of H<Subscript>2</Subscript>–O<Subscript>2</Subscript> mixtures in shock waves

The initiation of the autoignition of hydrogen–oxygen–argon mixtures behind reflected shock waves is studied by absorption and emission spectrophotometry in the temperature range of 960 < T < 1670 K at pressures of ~0.1 MPa. Introduction of Mo(CO)₆ additive in an amount of ~80 ppm made it possible to study the effect of O atoms on the shortening of the ignition delay time of H₂–O₂–Ar mixtures. A kinetic modeling of our own and published experimental data at temperatures of 930 < T < 2500 K and pressures of 0.05 < P < 8.7 MPa enabled to establish how the initiation reactions influence the process of self-ignition and to evaluate the rate constant for one of the initiation reactions: k(H₂ + O₂ → 2OH) = (3 ± 1) × 10¹¹exp(–E _a/RT), cm³ mol^–1 s^–1, where E _a = (40 ± 2) kcal/mol.     

EXAFS study of copper complexes with azomethinic ligand environment

A series of copper metallochelates C₂₂H₁₈CuN₄O₂ X (X = Se, S, O) as models of active centers of natural metalloproteins have been synthesized on the basis of new azomethine ligand systems. The structure of the complexes has been studied by extended X-ray absorption fine-structure spectroscopy. It is shown that, in the metallochelates with X = Se or S, one azomethine chalcogen-containing ligand undergoes tridentate interaction with copper ions, while the other ligand is an acetate group. As a result, a complex with the N₂O₂ X environment is formed, where one of the oxygen atoms of the acetate group is at a large distance from the metal ion: R = 2.56–2.68 Å. For the metallochelate with X = O, coordination of the acetate group by a copper ion is found to be absent, and only interaction with azomethine ligands having average Cu-N/O distances R = 1.96–2.04 Å is observed.     

Anlagerungskoeffizienten und Driftgeschwindigkeiten von Elektronen in Luft

Electron drift velocities and attachment coefficients were measured in dry air (E/p=0.1–30 V/cm Torr) and in a 9∶1 nitrogen/oxygen mixture (E/p=0.2–3 V/cm Torr) in the pressure range from 50 to 200 Torr, using a modified spark chamber technique. The primary electrons were released by anα-particle. The temporal development of the electron density in the gap was determined from the amplitude of the current due to the avalanches, which were produced by applying high voltage pulses at different delay times. — It was found that in air the dissociative attachment sets in at higherE/p (～10–15 V/cm Torr) than in oxygen. At lowerE/p three body attachment is predominant. — When the high voltage pulses were applied after the transit time of the primary electrons, electron avalanches still appeared. It was concluded that they were started by electrons which were detached from negative ions. The estimated detachment rates indicate the formation of O ₂ ^? ions at lowE/p and of O^? ions at higherE/p.     

Effect of oxygen impurity on the efficiency of the formation of complexes with H-bond and aggregation of color centers in lithium fluoride

The effect of impurities on the efficiency of the formation of color centers and hydrogen-bonded molecular complexes upon exposure to various radiations in lithium fluoride crystals grown in air is studied. The results of experiments for measuring optical properties, IR vibrational spectra, luminescence, and thermally stimulated luminescence are presented. The fact that the band in the range of 1800–2300 cm^–1 corresponds to stretching vibrations of a complex with strong hydrogen bond is proved based on the Fermi-resonance perturbation in the region of 2080 cm^–1, shaped as the Evans hole and bands A, B, and C. It is shown that the composition of these complexes includes an OH^– ion and an HF molecule. The crucial role of O^2? V _a ⁺ oxygen dipoles in the aggregation efficiency and gradient distribution of color centers and radiation resistance of hydroxyl ions is revealed. It is shown that products of radiation decomposition of OH^– ions stimulate, while decay of O^2? V _a ⁺ dipoles suppress, the formation of positively charged color centers.     

Mictomagnetic State in an EuBaCo<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5.5–δ</Subscript> Single Crystal

The magnetic properties of an EuBaCo_1.9O_5.36 single crystal are studied in the temperature range T = 2–300 K and the magnetic field range H ≤ 90 kOe. This binary layered cobaltite single crystal has vacancies in the cobalt and oxygen sublattices, in contrast to the stoichiometric EuBaCo₂O_5.5 composition. All cobalt ions in EuBaCo1.9O5.36 are in a trivalent state. The single crystal has an orthorhombic structure with space group Pmmm, and its unit cell parameters are a = 3.883 Å, b = 7.833 Å, and c = 7.551 Å. The field and temperature dependences of the magnetization of the single crystal demonstrate that it is ferrimagnet below T_C = 242 K. At T < 300 K, all three spin states of the Co³⁺ ions are present. The nearest-neighbor interactions give antiferromagnetic (AFM) and ferromagnetic (FM) contributions to the exchange energy. The ratio of the AFM to the FM contributions changes when temperature decreases because of a change in the spin state of the Co³⁺ ions. The single crystal exhibits signs of mictomagnetism at low temperatures in high magnetic fields. At T = 2 K and H = 90 kOe, the zero-field and nonzero-field magnetizations are strongly different because of a uniaxial magnetic anisotropy, which tends to set magnetization along the magnetic field applied in cooling throughout the crystal volume. As a result, a complex ferrimagnetic structure with a noncollinear direction of Co³⁺ spins appears. The following phenomena characteristic of mictomagnets are also observed in the EuBaCo_1.9O_5.36 single crystal: a shift in a magnetization hysteresis loop when temperature decreases, retained hysteretic phenomena and no magnetization saturation in high magnetic fields, and an orientation transition. The mictomagnetic state in EuBaCo_1.9O_5.36 is shown to be caused by the structural distortions induced by vacancies in the cobalt and oxygen sublattices and by the frustration of AFM and FM exchange interactions.     

Spin state of Co<Superscript>3+</Superscript> ions in EuBaCo<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5.5–δ</Subscript> in the paramagnetic temperature range

The magnetic studies of EuBaCo₂O_5.50, EuBaCo_1.93O_5.40, and EuBaCo_1.90O_5.36 have been performed. Layered cobaltites EuBaCo_2–x O_5.5–δ demonstrated the ferrimagnetic ordering in the temperature range 200 K < T < 650 K. The ferromagnetic Curie temperature T _C almost did not change as the number of Co³⁺–O–Co³⁺ bonds decreased. The contributions of the ferro- and antiferromagnetic interactions were nearly the same and determine the relationship T _C > T _N and T _C < T _N. At T > T _C, the antiferromagnetic order was retained in the EuBaCo1.90O5.36. As temperature increased, EuBaCo_2–xO_5.5–δ conserved the IS state in pyramids, and gradual LS → IS → HS transitions occurred in octahedron sites. The increase in the effective magnetic moment μeff in EuBaCo_1.90O_5.36 at T > 580 K demonstrated the transition of Co³⁺ ions to the HS state at lower temperatures as compared to the EuBaCo₂O_5.50 stoichiometric composition, and the structural distortions and the increase in the unit cell volume favored to this transition.     

Magnetic characteristics of MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles obtained by glycine–nitrate synthesis

The magnetic properties of magnesium–iron spinel (MgFe₂O₄) powdered nanoparticles obtained by glycine–nitrate synthesis are investigated by X-ray phase analysis and the NMR method. According to the results of X-ray phase analysis, the average size of the crystalline part of nanoparticles of the powder under investigation is 45 ± 4 nm. Magnetization J is determined using the formula J = (B/μ0)–H, where B and H are the induction and strength of the magnetic field in the sample, which are measured by the NMR method. The magnetic characteristics of MgFe₂O₄ are as follows: specific saturation magnetization J_sat = 17.52 A m²/kg, specific residual magnetization J_r = 5.73 A m2/kg, coercive force H_c = 4600 A/m, and magnetic moment P_sat = 371 × 10^–20 A m² in the magnetic saturation state and P_r = 121 × 10^–20 A m² in the residual magnetization state.     

Synthesis,structure, and optical and photocatalytic properties of quasi-one-dimensional ZnO doped with Со<Subscript>3</Subscript>O<Subscript>4</Subscript> and carbon

One-dimensional nanocomposites Zn_1–x Co _x O_1–y С _у :nCo₃O₄ and solid solutions Zn_1–x Co _x O_1–y С _у , which are promising photocatalysts for the oxidation of toxic organic compounds in visible light, are obtained via the thermolysis of Zn_1–x Co _x (HCOO)(OCH₂CH₂O)_1/2 (0.1 ≤ x ≤ 0.5) precursor in a controlled gaseous atmosphere.