Sonochemical nitrogen fixation for the generation of NO2− and NO3− ions under high-powered ultrasound in aqueous medium

Sonochemical species such as nitrite (NO₂⁻) and nitrate (NO₃⁻) were detected in ultrapure aqueous medium with 28 kHz low frequency ultrasound (US) in the range of 200–1200 W output power. The concentration of their anionic ions monitored with a high-performance liquid chromatography increased with increasing US power especially under air atmosphere. When the generation of NO₂⁻ and NO₃⁻ ions under US exposure was investigated for N₂, O₂ and Ar-bubbled solutions, no trace of NO₂⁻ was observed while NO₃⁻ was slightly generated. Under air atmosphere, the concentration of dissolved oxygen in the aqueous medium increased especially when 1200 W power was used. In addition, the bulk pH shifted towards the acidic side with an increase in exposure time, which indicated that NO₂⁻ was formed. The formation of oxidizing species under 28 kHz low frequency ultrasonic treatment was confirmed with an absorption spectrum which was dominated by two maxima peaks at 288 nm and 352 nm representing triiodide I₃⁻ anion.     

Ionoluminescence and formation of color centers in α-Al2O3 single crystals under proton irradiation

This paper describes results of experimental studies on radiation defects in nominally pure single crystals of corundum in two initial states: α-Al₂O₃ with an unperturbed lattice and α-Al₂O₃:C with a high concentration of anion vacancies. Defects were identified from optical absorption spectra, ionoluminescence, pulsed cathodoluminescence and photoluminescence spectra. It is shown that mostly color centers of the F- and F⁺-types are formed in the α-Al₂O₃ lattice under irradiation with 5,7 MeV protons.     

Formation of optical color and fluorescence centers in polytetrafluoroethylene under γ-irradiation

Fluorescent properties and colors of polytetrafluoroethylene (PTFE) samples were studied as functions of absorbed dose of γ-radiation at a temperature above the melting temperature of the crystallites (327°C) in the dose range 0.2–0.8 MGy. The samples were irradiated at low pressure (10^–6 Torr) in glass ampuls and at atmospheric pressure in a chamber purged with argon. Samples in ampuls acquired an off-white tint and fluoresced weakly. The fluorescence intensity increased slowly as the radiation dose increased from 0.2 to 0.6 MGy and decreased at 0.8 MGy. Samples irradiated in the chamber fluoresced more strongly and acquired colors that changed from gray (0.2 MGy) to dark-brown (0.8 MGy). Color centers were formed only in the sample surface layer. Their appearance was associated with the adsorption of particles of an unknown nature from the environment. The argon-purged samples turned white upon removing their surface layer (50 μm). The intensity and shape of fluorescence bands emitted by these samples remained essentially unaltered, i.e., depended weakly on the absorbed dose in the range 0.2–0.8 MGy.     

Study of the CO2-3 impurity in KTa1−xNbxO3

Infrared transmission and Raman scattering permitted the detection of CO^2-₃ impurities in KTaO₃ and KTa_1−xNb_xO₃ materials. These impurities could generate the observed anomalies in the physical properties of such compounds.     

First-principles study of crystal structures of NO+NO3− under pressure

First-principles calculations employing density functional theory are performed to study ionic crystal structures of NO⁺NO₃^?. The pressure dependences of enthalpy, structural parameters, and electronic band gap are investigated for the two experimentally reported phases of NO⁺NO₃^?. It is found that these two phases have comparable densities for P<25 GPa and are thus competing ones that may be obtained through different pathways. Moreover, one of the two phases is unlikely the previously proposed orthorhombic P2₁cn structure. The trend of pressure dependence of the band gap is typical of that for ionic crystals. This study provides insight into different experimental findings.     

Laser oscillation by the F3− and F2− color centers in LiF crystal at room temperature

A stable, free-running LiF:F₃ ⁻ and LiF:F₂ ⁻ color center laser oscillation is achieved at room temperature by pumping with the 930-nm laser radiation. The LiF:F₃ ⁻ laser radiation has a peak at 1100 nm and shifts from the peak wavelength of the F₃ ⁻ luminescence band because of the absorption of the F₃ ⁻ luminescence by the F₂ ⁻ center, which co-exists with the F₃ ⁻ center. Received: 2 March 1999 / Revised version: 16 March 1999 / Published online: 12 May 1999     

Intrinsic luminescence centers in γ- and θ-alumina nanoparticles

In this study, we investigate the photoluminescence(PL) properties of γ and θ-alumina nanoparticles synthesized by the chemical wet method followed by annealing. The obtained experimental results indicate the presence of some favorable near ultraviolet(NUV)-orange luminescent centers for usage in various luminescence applications, such as oxygen vacancies(F, F~+_2, F~(2+)_2, and F_2centers), OH related defects, cation interstitial centers, and some new luminescence bands attributed to trapped-hole centers or donor–acceptor centers. The energy states of each defect are discussed in detail. The defects mentioned could alter the electronic structure by producing some energy states in the band gap that result in the optical absorption in the middle ultraviolet(MUV) region. Spectra show that photoionazation of F and F_2 centers plays a crucial role in providing either free electrons for the conduction band, or the photoconversions of aggregated oxygen vacancies into each other, or mobile electrons for electrons-holes recombination process by the Shockley–Read–Hall(SRH)mechanism.     

Influence of CO 3 2− and OH− groups on dielectric losses of NaCl crystals

The results of measuring the dielectric losses of NaCl crystals with a different concentration of Na₂CO₃ and NaOH admixtures in the melt are given in the present paper. From a comparison of the curves found for the dielectric losses of the crystals studied it can be seen that the course of tan and the positions of the relaxation maxima, corresponding to the measured specimens with CO ₃ ^2– or OH^– admixtures, hardly differ. From these measurements and from a comparison with the results of other authors it follows that the admixture is probably the same in both groups of crystals.In conclusion the author thanks Dr. A. Bohun for discussions on the results and for his continuous interest in this work.     

Uncommon temperature dependence of the rotational motion of OH− centers in NaCl

Abstract

The correlation time τ_D of the rotational motion of OH^? centers in NaCl was studied for two different OH^?-concentrations (44 ppm and 220 ppm) between 0.5 K and 16 K by ²³Na nuclear spin relaxation measurements. The correlation time in the sample containing 44 ppm OH^? is given by phonon-assisted tunneling of isolated defects, whereas the OH^?-motion in the sample containing 220 ppm can be described by a coupled ensemble of quantum mechanical hindered rotators below a critical temperature which is determined by the strength of the interaction between the OH^? dipoles.     

Features of the twin structure of YBa2Cu3O7−x epitaxial films

X-ray diffraction is used to investigate YBa₂Cu₃O_7?x (YBCO) films on NdGaO₃(110) and a ${{(100)CeO_2 } \mathord{\left/ {\vphantom {{(100)CeO_2 } {(1\bar 102)}}} \right. \kern-0em} {(1\bar 102)}}Al_2 O_3 $ heterostructure. Symmetric, asymmetric, and axial geometries for θ and θ/2θ scans are used to obtain diffraction spectra from different crystallographic planes. The orientational and quantitative twinning characteristics of the films are determined. While the crystallographic parameters of these two types of film (the films are c-axis oriented with c=11.67 Å) are similar, there are differences in the twin structure. In particular, the features of the NdGaO₃ structure lead to the appearance of an angle differing from 90° (90.20°) between the possible (110) and θ/2θ twin planes in a YBCO film and a different number of twin components in each system of twins. It is concluded from an analysis of the broadening of reflections, which are sensitive to twinning, that there is not twinning in a 60% film of YBCO on Al₂O₃ with a CeO₂ buffer layer.     

Spin splittings in the ν3 band of NO2

Spin splittings for several important atmospheric lines in the ν₃ band of NO₂ have been measured by diode laser. An improved spin-splitting program has been developed which takes into account the asymmetry effects in the lower K_a splittings. The measured spin splittings and the derived spin-rotational constants are reported in this study to a much higher accuracy than previously achieved.     

Kinetics of accumulation and decay of paramagnetic centers in γ-irradiated doped phosphate glasses

The dose dependences and decay kinetics of PO ₄ ^2? and PO ₃ ^2? paramagnetic centers and radiation-reduced europium Eu^(3+)? in γ-irradiated phosphate glasses of composition 4Na₂O · La₂O₃ · 7P₂O₅ doped with europium are studied. The data obtained are discussed within the trapping volume model in the approximation of short irradiation duration. It is shown that the trapping volume parameter v decreases with increasing irradiation dose. A physical interpretation of the parameter v is proposed.     

Impurity magneto-optical absorption with the participation of resonance states of D 2 − centers in quantum wells

The dependence of the average binding energy of the resonance g-state of a D ₂ ^? center on the induction of an external magnetic field in a quantum well with a parabolic confining potential is studied using the zero-range potential method. It has been shown that with an increasing exchange interaction, the character of the dependence of the average binding energy of the resonance g-state of the D ₂ ^? center on the induction of the external magnetic field changes. It has been assumed that in GaAs/AlGaAs quantum wells alloyed with small Si donors, resonance D ₂ ^? states can exist under conditions of exchange interaction. It has been found that in spectra of impurity magneto-optical absorption in multiwall quantum structures, exchange interaction manifests itself as oscillations of interference origin.     

A Quantum-chemical study of the mechanism of formation of styrene polymerization centers under initiation by the ferrocene—benzoyl peroxide system

The mechanism of formation of free polystyrene growth radicals and radicals bound to complexes with ferrocene when polymerization was performed in the presence of the ferrocene—benzoyl peroxide initiating system was studied by quantum-chemical calculations with the use of the PRIRODA program and the PBE/3z method. The calculated structure of the charge transfer complex between ferrocene and benzoyl peroxide was in agreement with the experimental data. The calculated heat effects of possible complex decomposition reactions showed that radical formation easily occurred in the presence of the monomer only. The most favorable energetically scheme of the formation of the active centers of the complex-radical polymerization of styrene, including the intermediate formation of the ferrocene—benzoyloxy radical complex, was suggested.     

Color centers in the ionized and in the triplet state —Z 2 centers in calcium doped KCl crystals

Optical absorption measurements ofZ ₂ andZ ₂ ⁺ centers in KCl:Ca are combined with electron spin resonance experiments in order to reveal the electronic and atomistic structure of these centers.Z ₂ ⁺ centers are alignable in the crystal by polarized optical irradiation at suitable temperatures. From orientedZ ₂ ⁺ centers equally orientedZ ₂ centers can be produced, both types of centers showing a (100) axial symmetry. ConcerningZ ₂ this is also confirmed by ESR measurements on their triplet state produced by optical excitation. Polarized excitations allow a determination of the ratio of oscillator strengths for transitions parallel and perpendicular to the center axis using the variations in ESR line intensities. ForZ ₂ f /f =1.6 is found in this way; decomposition of the dichroism ofZ ₂ ⁺ centers gives for this speciesf /f =1.8. It is shown that theZ ₂(Ca) center is a molecule made up of a Ca⁺⁺ ion and an anion vacancy in (100) nearest neighborhood, sharing two electrons with antiparallel spins in the ground state. Both, withZ ₂ andZ ₂ ⁺ , the absorption bands at lowest energies are best explained bys—d charge transfer transitions.     

Features of the formation of electron bunches upon the development of generation in multiwave Čerenkov devices

The dynamics of electron bunch formation are analyzed using data obtained by means of numerical simulation. It is shown that upon the development of microwave generation, electron bunches start to form in a relativistic flow in the first section of the electrodynamic structure. At the entrance to the second section, a complex structure of electron distribution over a longitudinal pulse is observed inside the bunch in the stationary mode of generation. It is concluded that the duration of a microwave radiation pulse can be increased by optimizing the length of the first section of the generator.     

Dislocation centers in α-martensite formation and dual couplings of thinly-laminated martensite crystals

The spectrum of observable dual couplings of crystals of thinly-laminated martensite with habiti {3 15 10} is discussed within the framework of the concept of the dislocation formation of -martensite crystals. A spectrum of dislocation centers of formation arising together with the developing martensite crystal is proposed. Here it is essential to divide the arising dislocation centers of formation into two groups associated with different displacement mechanisms. This difference permits understanding of the difference in the frequency of observation of couplings and the introduction of the concept of a comb structure — a set of secondary parallel crystals of martensite, associated with the same initial crystal.Urals Forestry Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 64–67, June, 1994.