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1.
The 57Fe Mössbauer spectra of the single crystalline and the finely ground Sr1?x La x Fe12?y Co y O19 (x = 0 : y = 0, x = 0.192 : y = 0.152 and x = 0.456 : y = 0.225) samples have been measured to investigate the La-Co substitution effects. All observed spectra at 150 K were well fitted using the five subspectra which correspond to the five crystallographical nonequivalent Fe sites in the M-type hexaferrite, indicating that the valence changes to Fe2+ ions in the Fe3+ ions were not observed in our Sr1?x La x Fe12?y Co y O19 samples. In SrFe12O19, the relative absorption intensities in the five subspectra show the large anisotropies in the recoilless fractions at the five Fe sites whereas these anisotropies were not observed in Sr0.544La0.456Fe11.775Co0.225O19. These results indicate the chemical compositional dependence on the anisotropies of the recoilless fractions at the five Fe sites. The substitution of a Co2+ ion for the Fe3+ ion changes the center shifts of the Fe3+ ions near the Co2+ ion by the perturbation of the Fe-O-Co hybridizations. Therefore, the Co2+ ions occupy the 4f 1 and the 4f 2 sites due to the chemical compositional dependences of the refined magnetic hyperfine field and center shifts of the Fe3+ ions.  相似文献   

2.
The valence state of transition metal ions in the Co1–x Fe x Cr2O4 (x = 0.1, 0.2, 0.5) system has been investigated using X-ray photoelectron and Mössbauer spectroscopy. It has been shown that, in this system, there are Fe2+ and Fe3+ ions. The relative Fe3+/Fe2+ contents have been determined by fitting the experimental Fe 2p photoelectron spectra by a superposition of theoretical spectra of the Fe2+ and Fe3+ ions, as well as using Mössbauer spectroscopy.  相似文献   

3.
The refined set of values of the effective nuclear charge (\(\bar Z_{ef} \)) and the set of one-electron spin-orbital constants (ξ 3d teor ) are obtained for ions of transition metals with the help of a semiempirical method of calculation of the spectrum of free ions with allowance for the spin-orbital interaction. The effective nuclear charge, which is a variable theoretical parameter, was determined from a comparison of theoretically calculated ion absorption spectra with experimental ones. The form of the potential for the calculation of the spin-orbital constant was chosen such that the calculated value ξ 3d teor would coincide with the experimental one ξ 3d exp . The calculated set of values \(\bar Z_{ef} \), ξ 3d teor } can be used in semiempirical calculations of energy levels of 3d ions (ions with an incomplete 3d shell).  相似文献   

4.
The energy losses of fast structural ions in collisions with atoms have been considered in the eikonal approximation. The structural ions are ions consisting of a nucleus and a certain number of electrons bound to it. The effect of nuclear charge Z of the ion on its effective deceleration κ(p) (energy losses associated with excitation of only intrinsic ion shells) has been analyzed. It is shown that the allowance for the interaction of an atom with the ion nucleus for Z a Z/v > 1, where Z a is the charge of the atomic nucleus and v is the velocity of collisions in atomic units, considerably affects the value of κ(p), which generally necessitates taking into account nonperturbatively the effect of both charges Z a and Z on κ(p).  相似文献   

5.
A modified Poisson-Boltzmann model has been proposed which makes it possible to describe the screening of strongly charged macroparticles in liquid electrolyte Z: Z solutions in the case when parameter B= ZeQ0RT?1(Q0 is the surface electric charge, T is the temperature, ε is the solution permittivity, and Z is the valence of ions) provided that the solution is dilute: κR ≡ (8πZ2e2ni0T)1/2R?1 (ni0 is the equilibrium number density of ions). It is assumed that the charge Q0 of a macroparticle appears as a result of adsorption of ions of a certain polarity on its surface. Quantitative criteria of division of dissolved ions into capable and incapable of adsorption are formulated. For aqueous solutions, the adsorption mechanism always leads to values of B ? 1. It is shown that the charge inversion effect predicted by other authors on the basis of different models must be observed for such solutions for all Z ≥ 1. The effect of Brownian movement of macroparticles on their screening is considered. It is shown that viscous forces emerging during such movement lead to peripheral destruction (“washing out”) of the screening ionic shell of macroparticles and, as a result, to violation of their electroneutrality. This results in the emergence of two types of oppositely charged compound particles with small radii close to R and with radii much larger than R, the charge polarity of the latter being opposite to the polarity of Q0. It is found that both types of ions of compound particles obey the “law of distribution” of the mean energy of their electric field, expressed by formula (29). The problem of ionic screening of gas bubbles accompanied by the formation of bubstons (bubbles stabilized by ions) is considered separately. It is shown that the bubston radius R in pure water and in aqueous solutions of electrolytes is equal to 14 nm irrespective of the ion number density ni0. The value of ni0 determines the number density n b of bubstons themselves, which are formed spontaneously under equilibrium conditions.  相似文献   

6.
The attachment of radioactive atoms and ions to spherical aerosol particles has been studied theoretically. For uncharged atoms the deposition is considered to be solely governed by thermal diffusion. With calculations based on the “limiting-sphere”-method ofArendt-Kallman it is found, that the attached activity is proportional toΦ 2 for aerosol particle diametersΦ smaller than 0.1 μm, and proportional toΦ forΦ greater than 1 μm. For charged ions the diffusion process is modified by the influence of electrostatic forces between the diffusing ions and the aerosol particles. In the frequently occurring case of a symmetrically bipolar charged aerosol this influence can be expressed by a functionG p(Φ), which depends on the diameterΦ and the effective numberp of elementary charges on the aerosol particle. For an aerosol particle diameterΦ greater than 0.1 μm the attached activity is proportional toΦ 1.1, and forΦ smaller than 0.01 μm it is proportional toΦ 1.55. The effects of neglecting various terms in the calculation are considered. The distribution of natural radioactivity on atmospheric aerosols has been calculated for various particle size distributions according toJunge. The calculation shows that about 90% of the total natural activity should be attached to particles smaller thanΦ=0.5 μm, and about 35% to particles smaller thanΦ=0.1 μm. The time T1/2, in which the concentration of the radioactive particles decreases to half the initial value, depends on the concentration of the aerosol particles and on their size distribution. For 104 aerosol particles per cm3 and the size distributions mentioned,T 1/2 varies between 15 and 30 seconds for radioactive ions. For radioactive atomsT 1/2 is greater than it is for ions in the range of aerosol particle diameters belowΦ=0.25 μm, and smaller ifΦ greater than 0.25 μm.  相似文献   

7.
The results of studies of the absorption spectra of nickel orthoborate Ni3(BO3)2 in the range of electronic dd-transitions are reported. The obtained data are analyzed in the framework of the crystal field theory. The Ni2+ ions are located in two crystallographically nonequivalent positions 2a and 4f with point symmetry groups C2h and C2, respectively, surrounded by six oxygen ions forming deformed octahedra. The absorption spectra exhibit three intense bands corresponding to spin-resolved transitions from the ground state of nickel ion 3A2g (3F) to the sublevels of the 3T2g (3F), 3T1g (3F) and 3T1g (3P) triplets split by the spinorbit interaction and the rhombic component of the crystal field. At temperatures below 100 K, the spectra exhibit a thin structure, in which phonon-free lines can be distinguished. Comparison of the calculated frequencies of the zero-phonon transitions with the experimental data allows estimating parameters of the crystal field acting on the nickel ions in the 2a- and 4f-positions, as well as the parameters of electrostatic interaction between the 3d electrons and spin-orbit interaction constants.  相似文献   

8.
We present an ab initio calculation of the screened self-energy correction for 1s2 2p3/2 and 1s2 2s states of Li-like ions with nuclear charge numbers in the range Z = 12?100. The evaluation is carried out to all orders in the nuclear strength parameter Zα. This investigation concludes our calculations of all two-electron QED corrections for the 2p3/2-2s transition energy in Li-like ions and thus considerably improves theoretical predictions for this transition for high-Z ions.  相似文献   

9.
The method of extrapolation of the parameter of a model potential for states of one electron (4f, 5s, 5p, 5d, 5f) above the core 1s 22s 22p 63s 23p 63d 104s 24p 64d 10 and one vacancy (4d 9) in the same core is applied to calculate the energy levels in the silver and rhodium isoelectronic sequences with the maximum nuclear charge Z = 86. The energy levels of Ag-and Rh-like ions were used for the calculation of the energies of resonance transitions to the ground state 1 S 0 in Pd-like ions. Good agreement between the theoretical and calculated energies of the resonance transitions in Pd-like ions indicates the reliability of the results obtained.  相似文献   

10.
Pioneering theoretical data for single-electron charge transfer and excitations due to collisions between Bi4+ ions in the ground (6s) and metastable (6p) states are gained in the collision energy interval 5–75 keV in the center-of-mass frame. The cross sections of the processes are calculated in terms of the close-coupling method in the basis of two-electron quasi-molecular states for the Coulomb trajectory of nuclei. It is found that single-electron capture into the singlet 6s 2 states of Bi3+ ions makes a major contribution to the charge transfer total cross section for Bi4+(6s) + Bi4+(6s) collisions (reaction 1), whereas single-electron capture into the singlet 6s6p states is the basic contributor to the total cross section in Bi4+(6s) + Bi4+(6p) collisions (reaction 2). In the collision energy interval mentioned above, the collision cross sections vary between 1.2 × 10?17 and 1.9 × 10?17 cm2 for reaction 1 and between 3.8 × 10?17 and 5.3 × 10?17 cm2 for reaction 2. In reaction 1, the 6s → 6p excitation cross sections vary from 0.6 × 10?16 to 0.8 × 10?16 cm2 for the singlet channel and from 2.2 × 10?16 to 2.8 × 10?16 cm2 for the triplet channel. The calculation results are compared with the data obtained in experiments with crossed ion beams of kiloelectronvolt energy. The fraction of metastable ions in the beams is estimated by comparing the experimental data with the weighted average theoretical results for the cross sections of reactions 1 and 2. From the data for the charge transfer cross sections, one can estimate particle losses in relativistic beams due to a change in the charge state of the ions colliding with each other in the beam because of betatron oscillations.  相似文献   

11.
The fundamentals of the theory of the electronic structure of impurity clusters and the results of numerical calculations for the iron-, lanthanum-, and actinium-group ions in Me+n: [L]k clusters are presented. The effects of the interionic distance and ligands in the Me+n: [L]k clusters on the electronic structure of the nl N and nlN?1nl′ configurations of the 3d, 4f, and 5f ions are considered. The correspondence between the optical and x-ray spectra of different impurity crystals is also analyzed.  相似文献   

12.
From oscillograms of avalanches of high amplification (ether,p=370 Torr,d=0,3 cm,E/p=77) one can deduce that the number of carriers (n) increases less thane αx , ifn overpasses 106. It is the space charge field of the positive ions which reduces the ionisation effect of electrons.  相似文献   

13.
Systematic calculations of the probabilities and energies of radiative transitions in doubly excited 3l3l′, 3l4l′, and 4l4l′ states of oxygen, carbon, and nitrogen ions have been carried out within the Hartree-Fock approximation. The emission spectra are obtained, and analysis of the changes in the spectral characteristics with a change in the charge and the number of additional electrons in the ground state of the initial ion is performed. The data obtained are used to interpret the X-ray spectra of the atmospheres of planets and comets.  相似文献   

14.
We have investigated the photoproduction of triplets on free electrons, γee+ee, in which dark photon A′ can be formed as an intermediate state with subsequent decay into an e+e pair. This effect appears as a result of the so-called kinetic mixing and is characterized by the small parameter describing the intensity of the interaction of the dark photon with charged Standard Model (SM) particles in terms of electric charge e. The search for a manifestation of A′ in this process is advantageous since the background to the A′ signal is purely electrodynamic and, hence, can be calculated with the required accuracy. We calculate this background taking into account the identity of final electrons. As regards A′, its contribution is taken into account only in Compton-type diagrams (of virtual Compton scattering) in which a virtual dark photon is a time-like particle and its propagator has the form of a Breit–Wigner resonance. It is only in the vicinity of resonance that A′ can be manifested. We calculate the invariant mass distribution of both e+e pairs formed in the process and analyze the kinematic region in which relatively small squares of momenta transferred from the target electron to the formed electrons are excluded. In these conditions, the contribution to the differential cross section from Compton-type diagrams is not suppressed relative to the contribution of the remaining (Borsellino) diagrams. A number of limitations on parameter depending on the dark photon mass and the statistics (number) of events are obtained for a special method of gathering events in which the invariant mass of one e+e pair remains fixed and of the other pair is scanned.  相似文献   

15.
The hyperfine-structure spectra of the 14.4 keVγ-ray of the nucleus57Fe in the spinel type ferrite (Li 05 + Fe 1.3 3+ Cr 1.2 3+ O 4 2? ) have been measured through the use of the Mößbauer effect. These measurements were performed on powder samples at different temperatures between 88 °K and 633 °K. For the Fe3+ ions at both the tetrahedral (A) and octahedral (B) sites at 88 °K the effective magnetic fieldH at the Fe nuclei is the same and equal to 504±4 kG. The temperature dependence ofH A however is different fromH B . Application of an external magnetic field of 20 kG shows that the sign ofH A is positive and the sign ofH B is negative. As the temperature is increased a considerable broadening of the magnetic hfs-lines (and especially of the outer pair of lines) is observed. No theoretical discussion directly applicable to these measurements is as yet available. In the paramagnetic phase a well resolved doublet is obtained. It appears that this doublet must be interpreted as a quadrupole splitting.  相似文献   

16.
The effect of high doses on p-and n-type silicon samples implanted with Fe+ ions under steady-state conditions (implantation energy, 100 keV; ion current density, 0.6–0.8 μA/cm2; irradiation dose, 1014–1016 ions/cm2) is investigated using Si L 2, 3 x-ray emission spectroscopy (the 3d3s → 2p electronic transition). An analysis of the Si L x-ray emission spectra of the silicon samples is performed by comparison with the spectra of reference materials and the spectra of silicon samples implanted with Fe+ ions in a pulsed mode. The Si L x-ray emission spectra are simulated by the molecular dynamics and full-potential linearized augmented-plane-wave (FLAPW) methods. It is revealed that the effect of high doses under steady-state conditions of Fe+ ion implantation into the semiconductor crystal matrix exhibits specific features: the disordering of the structure and partial amorphization of the sample from the surface deep into the bulk are more pronounced than those observed under conditions of pulsed ion implantation, although virtually no recrystallization of the sample at the threshold dose occurs. The most probable origins and mechanisms of the effect of high doses on the samples under investigation are discussed.  相似文献   

17.
High-temperature field evaporation of tungsten and tantalum emitters in the temperature range from room temperature to 2500 K is studied using a static magnetic mass spectrometer equipped with a field source of ions. At room temperature, triply charged W3+ and Ta3+ ions alone are observed in the mass spectra. However, as the emitter temperature grows, the charge of the ions decreases. At T ≈ 1000 K, doubly charged W2+ and Ta2+ ions dominate in the spectra, and singly charged W+ and Ta+ ions appear in the temperature range 1900 < T < 2500 K. The evaporation rate of the singly charged ions is one to two orders of magnitude lower than the evaporation rate of the doubly charged particles. The energy parameters of field evaporation for differently charged tungsten ions are found.  相似文献   

18.
Radiative lifetimes for the 4d94f, 4d95p, 4d95d, and 4d96s levels in the spectra of palladium-like ions Pr XIV and Nd XV are calculated in the electric-dipole approximation by the intermediate coupling semiempirical method with the use of experimental energy levels available in the literature. The radial integrals of transitions necessary for calculating absolute values of transition probabilities are obtained in the length form with Hartree–Fock functions.  相似文献   

19.
The structure of the outer and inner electron spectra of iron (2p, 3p, 3s, and 3d) and phosphorus (3s and 3p) atoms in FeP monophosphide is studied in detail by the X-ray photoelectron spectroscopy (XPS) method. On the basis of the analysis of the binding energy of electrons, as well as the parameters characterizing the structure of experimental spectra, a conclusion is made that Fe3+ (d 5) cations in FeP are stabilized in a state with intermediate value of the total spin (IS, S = 3/2). The range of values of intra-atomic parameters (10Dq, J H ) is established in which the consideration of the high degree of covalence of Fe–P bonds may lead to the stabilization of (FeP6)15– clusters in the IS state.  相似文献   

20.
Polarization spectra of optical absorption of the 4f-4f transition 6 H 15/26 F 3/2 in the rare-earth orthoaluminate DyAlO3 are theoretically and experimentally studied at the temperature T=78 K. It is shown that the nontrivial character of the anisotropy of the polarization absorption spectra at low temperatures can be explained by the J-J mixing of excited multiplets of the 4f 9 configuration of Dy3+ ions in a low-symmetry crystal field of the orthoaluminate structure. The energy and wave functions of the Stark sublevels within the excited 6 F 5/2 multiplet in the 4f 9 configuration of the Dy3+ rare-earth ion in the crystal field of C s symmetry are numerically calculated.  相似文献   

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