Cation distribution in NixMg1−xFe2O4 studied by XPS and Mössbauer spectroscopy

Ni–Mg ferrites, synthesized by solid-state route, were analyzed by X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy to find the distribution of Mg²⁺ in tetrahedral (A) and octahedral (B) sites of the spinel. In Ni_xMg_1−xFe₂O₄, Ni²⁺ enters in B site resulting in a reduction in the availability of B sites for the distribution of Mg²⁺ and Fe³⁺ and thereby influences the distribution of Mg²⁺. It was observed through both techniques that higher percentage of Mg²⁺ occupied the tetrahedral sites of Ni rich spinel systems. Thermodynamic considerations showed that entropy played significant role in the distribution of Mg²⁺ in Ni_xMg_1−xFe₂O₄, in addition the difference in site preference energy between Fe³⁺ and Mg²⁺ was too small to cause any influence.     

高能电子对原子核C12的弹性散射

In this paper, we have calculated the elastic scattering of high energy electrons with nuclei C¹² by phase shift calculation.We take the charge distribution of the nucleus C¹² as following:(1) exponential distribution:ρ(x)=ρ₀θ^-x/a, (2) gaussian distribution:ρ(x)=ρ₀e^(-x2/a2),(3) uniform distribution: ρ(x) ={ρ₀ when 0kR, where a and b are the parameters, and the constant R is the radius of the nucleus C¹². The energy of the electrons is 187 Mev.The result of the calculation shows that the gaussian distribution confirms the experimental result better than the other two kinds of distributions, and gives R=(12)^1/3r₀, where r₀=1.35×10^-13 cm.     

Equilibrating of 15N-Gases by Electrodeless Discharge: A Method of Indirect Mass Spectrometric Analysis of 30N2 for Denitrification Studies in Soils

Abstract

The estimation of denitrification in soil by the ¹⁵N tracer technique includes isotope analysis of gas samples with a nonrandom distribution of the N₂ mole masses of 28, 29 and 30. In that case the emission of total ¹⁵N is underestimated by calculating ¹⁵N atom fractions from the ²⁹N₂/²⁸N₂ ratio if ³⁰N₂ is not considered. ³⁰N₂ can be measured indirectly in N₂ enriched with ¹⁵N with nonrandom distribution of mole masses by mass spectrometric analysis. The nitrogen fraction of gas samples was transferred to discharge tubes. Microwaves (60 sec) generated an electrodeless discharge of the gas which caused a temporary split-up of N₂ molecules and thus established an equilibrium distribution of the mole masses. The ²⁹N₂/²⁸N₂ ratio was measured in equilibrated and in untreated samples to calculate the real emission of ¹⁵N. The measurements of ¹⁵N standard gases by this method satisfactorily coincided with calculated values for ¹⁵N atom fraction above a concentration of 50 δ‰.     

The analysis of nitrogen rotational and vibrational bands in a helium microhollow gas discharge

Emission spectroscopy is applied to measure the gas temperature T _g and the vibrational distribution of N₂ (C ³Π_u) and N₂ ⁺(B ²Σ_u ⁺) excited states from a helium microhollow gas discharge (MHGD) at atmospheric pressure. The rotational temperature T _rot of N₂ ⁺ is determined from relative intensity of the R‐branch lines of the N₂ ⁺(B ²Σ_u ⁺–X ²Σ_g ⁺) bands at 427.81 and 419.91 nm and the well‐known Boltzmann plot (BP). Using the same diagnostic technique, the rotationally resolved N₂(C ³Π_u–B ³Π_g) band at 380.49 nm is used to measure T _rot. Under our experimental conditions, T _g is equal to T _rot = 550–650 K for nitrogen molecules and shows a slight increase with the discharge current in the current range 3–10 mA. From the intensity ratio of two consecutive vibrational bands of the same sequence, the N₂(C ³Π_u) and N₂ ⁺(B ²Σ_u ⁺) vibrational temperature T _vib = 3,700–4,000 K is determined. It has been found that N₂ ⁺(B ²Σ_u ⁺) ions have non‐Boltzmann distribution in the helium MHGD, while N₂(C ³Π_u) molecules are populated according to the Boltzmann distribution. Following the Franck–Condon principle, the vibrational distribution of the ground state of N₂(X ¹Σ_g ⁺) molecules has been determined from the N₂(C ³Π_u) distribution using the inversion matrix of elements q _XC(ν ,ν ′).     

Determination of temperature in a plasma jet emanating from a plasma torch with sectioned inter-electrode insert from the molecular emission spectrum of nitrogen

Results of application of a method for measuring the distribution of temperature in a nitrogen plasma jet emanating from a dc plasma torch with sectioned inter-electrode insert from the relative intensities of the molecular emission bands of nitrogen in the N₂ ⁺(B²Σ_u ⁺ − X²Σ_g ⁺) first negative and N₂(C³Π_u ⁺ − B³Π_g ⁺) second positive systems are reported. The emission spectra were registered using a small-size spectrometer with medium-range spectral resolution enabling a contour analysis of ro-vibrational bands in molecular emission spectra. The obtained distribution of temperature was compared with the distribution that was determined from the emission lines due to copper atoms and with the mean-mass plasma temperature of the air plasma jet.     

An approximate expression for the Wigner-Kirkwood ℏ4 quantum correction to the pair distribution function in a one-component plasma

We propose an accurate approximate expression for the exact ℏ⁴ quantum correction to the pair distribution function g₂^q(r₁₂) that we have derived recently in an OCP using Wigner-Kirkwood ℏ² expansion. Our expression, depending only the classical pair distribution function g₂^c(r₁₂), reproduces the behavior of Wigner-Kirkwood g₂^q(r₁₂) at order ℏ⁴, at small, intermediate and large r₁₂.     

Laser spectroscopy of spinel microcrystallites in a Cr3+ doped silicate glass

Laser spectroscopy of Cr³⁺ ions makes it possible to follow the crystallization process in a cordiente glass (52 SiO₂, 347 Al₂O₃, 12.5 MgO and 08 Cr₂O₃) Absorption and fluorescence are interpreted by structural considerations showing the variation of Cr³⁺ environment during heat treatment Fluorescence line narrowing is performed at 4 2 K giving information on the detailed crystal structure in MgAl₂O₄ spinel microcrystallites formed during heat treatment The splitting of the ²E level is close to 70 cm^?1 and the ¦2D¦ parameter ranges between 0 95 and 1 35 cm^?1 This wide distribution is associated with the well known disordered distribution of Mg²⁺ and Al³⁺ cations in MgAl₂O₄ spinels.     

X-ray diffraction study of ion thermal vibrations in R2CuO4 (R=Pr and Gd) crystals

An X-ray diffraction study is reported of the symmetry in the spatial distribution of thermal vibrations of Cu₂₊, Gd³⁺, and Pr³⁺ ions in Gd₂CuO₄ crystals. An analysis of the pattern of the angular thermal-vibration amplitude distribution obtained experimentally at different temperatures allows a conclusion about the character of the local Jahn-Teller effect for the Cu²⁺ ions, structural phase transitions, and the orbital ground state of the Cu²⁺ ions.     

Connection between elastic scattering and inclusivek T 2 distribution

A connection between the elastic scattering and the inclusive one-particlek _T ² distribution is pointed out in the context of thes channel unitarity. One of the implications of this connection is that the slope of thek _T ² distribution atk _T ² =0 is about a factor two larger than the slope of the elastic scattering att=0.     

Direct measurement of lifetimes of infrared multiple-photon dissociated molecules

A beam of mass selected SF ₅ ⁺ ions is crossed with a pulsed CO₂ laser beam. The distribution of lifetimes of infrared multiple-photon pumped SF ₅ ⁺ ion-molecules prior to dissociation into SF ₄ ⁺ +F has been measured directly using a time-of-flight ion-beam technique. The data provide new information on the distribution of the total internal energy of molecules excited by absorption of infrared radiation.     

Electron hopping in Fe1−xCuxCr2S4 (0<x<0.5)

A theoretical expression for the line shape of the Mössbauer spectra in the presence of electron hopping between Fe²⁺ and Fe³⁺ is obtained by using a simple stochastic model. Analyses based upon this expression show that the origin of the complicated Mössbauer spectra observed in the magnetic semiconductors Fe_1?xCu_xCr₂S₄ (0<x<0.5) at 77 K is electron hopping between Fe⁺² and Fe³⁺ This hopping occurs at a rate of a few MHz. Quantitative estimates are given for some parameters; the isomer shifts, the internal magnetic fields, the quadrupole splittings and the proportions of Fe²⁺ and Fe³⁺. The valence distribution in this system is determined from the results. For example, the distribution Fe²⁺_0.69Fe³+_0.29Cu¹⁺_0.02Cr³⁺_1.72Cr²⁺_0.28S^2?₄ is obtained for x = 0.02. The existence of Cr²⁺ is concluded.     

Secondary ion emission from Si under nitrogen ion bombardment

The yield and energy distribution of positive secondary ions emitted from Si under N₂⁺ ion bombardment were measured. The obtained mass peaks correspond to three types of secondary ion species, that is, physically sputtered ions (Si⁺, Si₂⁺), chemically sputtered ions (SiN⁺ Si₂N⁺) and doubly charged ions (Si²⁺). The dependence of secondary ion emission on the primary ion energy was studied in a range of 2.0–20.0 keV. The yields of physically and chemically sputtered ions were almost independent of the primary ion energy. The yield of the doubly charged ion strongly depended on the primary ion energy. The energy distribution of secondary ions of the three types showed the same dependence on the primary ion energy. The most probable energy of the distribution increased with the primary ion energy. On the other hand, for the energy distribution curves of sputtered ions, the tail factors N in E^?N were constant and showed a m/e dependence.     

Field-induced ionization and Coulomb explosion of nitrogen

Femtosecond-laser field-induced ionization and Coulomb explosion of diatomic nitrogen were systematically investigated using time-of-flight mass and photoelectron spectrometry. Both linearly and circularly polarized femtosecond laser pulses were used at intensities varying from 5×10¹³ to 2×10¹⁵ W/cm². Strong N₂ ⁺, N₂ ²⁺, N⁺, N²⁺ and N³⁺ ion signals were observed for horizontally polarized pulses. Moreover, signals from the atomic ions exhibited a double-peak structure. Suppression of ionization was observed for circularly polarized pulses, while for vertically polarized pulses, only N₂ ⁺ and N₂ ²⁺ ions were observed. The angular distributions of the ions were measured under zero-field conditions in the ionization zone. The atomic ions N⁺, N²⁺ and N³⁺ exhibited highly anisotropic distributions, with maxima along the laser polarization vector and zeroes normal to the laser polarization vector. In contrast to the atomic ions, N₂ ⁺ exhibited a strong isotropic angular distribution. These observations indicate that dynamic alignment is responsible for the observed anisotropic angular distribution of the atomic ions. The kinetic energy spectrum of the photoelectrons is featureless and broad, extending above the ponderomotive potential of the laser pulse. The angular distribution is markedly anisotropic, with a maximum along the laser polarization vector. These observations further support the notion that the field-ionization mechanism is dominant under our experimental conditions. Received: 29 January 2002 / Revised version: 15 March 2002 / Published online: 12 July 2002     

Electronic-excitation transfer collisions in flames—VI. Interpretation of the temperature dependence of alkali-quenching by N2 and general conclusions about the energy transfer mechanism

The experimental temperature dependence of alkali-N₂ quenching cross sections is explained semi-quantitatively by a simple theoretical model, based on an ionic intermediate state, in which attractive van-der-Waals forces play an essential role. Using this model, quenching experiments are compared with Na(3²P)-N₂ excitation measurements in molecular beams. From this comparison it is concluded that the distribution of relative cross sections for specific vibrational transitions during the quenching process can be described by a distribution calculated by Fisher,⁽⁸⁾ whereas the distribution given by Bjerre⁽¹⁸⁾ has to be rejected. Resonant vibrational-electronic energy transfer is not important.     

Recombination population of highly excited CO2 states in a shock-heated jet

The spectral distribution of nonequilibrium emission from electron bands of partially dissociated CO₂ in a supersonic jet was studied. A detailed model of kinetic and energy-exchange processes in a vibrationally nonequilibrium recombining CO₂ flow is elaborated. Within this model, the basic kinetic equation for the distribution of CO₂ excited state populations was solved in a ladder approximation. It is shown that inverse population for the ³ B ₂ → X ¹Σ transition (λ=400 nm) is a possibility. The effect of mixture and flow parameters on the population inversion for electron vibrational transitions in CO₂ was analyzed.     

A new approach to calculate the gluon polarization

We derive the Leading-Order (LO) master equation to extract the polarized gluon distribution G(x,Q ²)=xδg(x,Q ²) from polarized proton structure function, g^p₁(x,Q²)g^{p}_{1}(x,Q^{2}). By using a Laplace-transform technique, we solve the master equation and derive the polarized gluon distribution inside the proton. The test of accuracy which is based in our calculations on two different methods, confirms that we achieve to the correct solution for the polarized gluon distribution. To determine the polarized gluon distribution xδg(x,Q ²) more accurately, we only need to have more experimental data on the polarized structure functions, g₁^p(x,Q²)g_{1}^{p}(x,Q^{2}). Our result for polarized gluon distribution is in good agreement with some phenomenological models.     

The structure of concentrated NiCl2 aqueous solutions: what is molecular simulation revealing about the neutron scattering methodologies?

An analysis is made of adequacy and limitations of the neutron weighted ion distribution function for the determination of the hydration ion structure in hydrothermal solutions. Our analysis indicates that the coordination number based on the O—Ni²⁺ interactions is unambiguously defined by the first peak of the neutron weighted cation distribution function G _Ni(r), but that the corresponding H—Ni⁺² and H—Cl^? coordination numbers may be ill-defined due to the occurrence of Ni⁺²-Cl^? ion pairing. For the system considered in this work, this effect contributes about 1.5 units to the H—Ni^?2 and 0.85 units to the H—Cl^? coordination numbers, respectively, for a 3.9 M NiCl₂ aqueous solution under ambient conditions. A comparison under ambient conditions between the most reliable NDIS data on Ni²⁺ hydration and our simulation results suggests that the present intermolecular potential models underestimate the O-Ni⁺² coordination numbers by about 1.5 units, and it might indicate the need for a reparametrization of the current ion-water intermolecular potentials. The hydration structure exhibits practically no temperature dependence for the isochore studied (1.356 g cm^?3) and composition. The Ni⁺²-Cl^? ion pair formation appears to affect the location of the shoulder in the neutron weighted distribution functions G _Ni(r) and G _Cl(r), although it does not affect the magnitude of the ion—water coordination.     

Mössbauer study of Zn2+ and Sn4+ additives in Nickel ferrites

The Mössbauer study of Fe⁵⁷ in polycrystalline solid solutions of Ni_{1 + x ? y}Zn_ySn_xFe_{2 ? 2x}O₄ (y = 0.1, 0.3, 0.5 and x = 0.1 to 0.5 with x varying in steps of 0.1) has been made. The present work has been aimed at investigating the variation of isomer shift, nuclear magnetic field at Fe⁵⁷ nuclei and ionic distribution at tetrahedral and octahedral sites when the concentration of Zn²⁺ and Sn²⁺ ions is successively increased in nickel ferrites. The ionic distribution in samples having low tin concentration has been explained on the basis of Neel's molecular field model whereas the ionic distribution of samples having high tin and zinc concentration has been explained on the basis of formation of isolated superparamagnetic clusters at the octahedral site. It has been inferred that a larger substitution of zinc and tin ions enhances relaxation effects.     

57Fe hyperfine interactions in M1 and M2 sites of olivine from Omolon meteorite: study using Mössbauer spectroscopy

Study of olivine (Fe, Mg)₂SiO₄ from Omolon meteorite was performed using Mössbauer spectroscopy with a high velocity resolution at 295 and 90 K. Components related to ⁵⁷Fe in crystallographically non-equivalent M1 and M2 sites in olivine were determined and its Mössbauer hyperfine parameters were evaluated at both temperatures. A Fe^2?+?–Mg^2?+? distribution coefficient and a temperature of cation equilibrium distribution for olivine from Omolon were evaluated on the basis of Mössbauer parameters.