双原子填充式skutterudite化合物的结构及X射线光电子能谱分析

用高温熔融、淬火、扩散退火结合放电等离子烧结(SPS)法合成了Ca和Ce复合填充的单相Ca_mCe_nFe_xCo_4-xSb₁₂(m=0.17—0.27，n=0.05—0.25，x=1.5)化合物，并结合Rietveld结构解析以及X射线光电子能谱(XPS)分析研究了两种原子复合填充skutterudite化合物的结构与填充状态.Rietveld结构解析表明，Ca_mCe_nFe_1.5Co_2.5Sb₁₂化合物具有skutterudite结构，Ca和Ce原子填充到了Sb的二十面体空洞中，填充原子热振动参数B_Ca/Ce远大于框架原子的热振动参数B_Fe/Co和B_Sb.XPS元素窄区谱分析结果表明，Sb原子在结构中有五种化学状态，每种化学状态的相对含量主要由总填充分数决定，填充原子Ca在Sb的二十面体空洞出现概率有三种可能，但在中心位置出现的概率最大. 关键词： skutterudite化合物 双原子复合填充 结构 X射线光电子能谱分析     

Effect of disorder on the magnetic properties of a partially filled skutterudite

The magnetic properties of the partially filled skutterudite Eu(0.5)Co(4)Sb(12) are investigated by a model Hamiltonian, with special emphasis on the effect of ordering and disordering occupancy of the filler atoms Eu on the magnetic properties. The magnetization, magnetic specific heat and entropy are calculated within the mean-field approximation. By introducing the position disorder of the filler atoms, the critical temperature T(C) above which the magnetization disappears is changed. The magnetization curve near T(C) also becomes concave compared to the convex magnetization of the ordered system. The filler disordering also leads to a kink in the isothermal magnetization curve and a valley in the magnetic specific heat near T(C). The effective magnetic field acting on the localized spin of the filler atoms has a competitive effect with the disorder and therefore makes the valley disappear.     

Propagation of electromagnetic waves in channeling systems partially filled by magnetoactive solid-state plasma

Results are given of the theoretical and experimental investigation of the propagation of waves of the superhigh-frequency range through cyclindrical and rectangular waveguides partially filled with anisotropic solid-state plasma. The definitive role of the frequency of collisions of charge carriers on the character of the dispersion is demonstrated and the possibility is indicated of the existence of retarded reverse waves in the structures under consideration.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 9, pp. 7–13, September, 1973.     

Electron channeling,structure factor phases,polarity and atom site determination in crystals

We relate element characteristic electron energy losses and the accompanying X-ray emission under electron channeling conditions to the phases of structure factors. We discuss examples illustrating that structure factor phase information can be extracted from two-beam channeling experiments. This information has been used by several investigators to determine the absolute orientation of non-centrosymmetric crystals. We further discuss how the success of electron channeling in locating atoms in the crystal unit cell, ALCHEMI, is tied to phase information beyond the conventional one. From the perspective of diffraction-based crystallography, ALCHEMI provides information about the phase with which a particular element scatters into a reflection. Therein lies the strength of the ALCHEMI technique as compared to relying on diffraction intensities for the location of small concentrations of elements and neighbors in the periodic system.     

Tees on partially filled rectangular waveguides

We propose an analytical solution of the problem of determination of external parameters of T-shaped E and H tees on partially filled rectangular waveguides. The solution is tested for a particular case of E and H tees on hollow rectangular waveguides and compared with the known solution obtained by the numerical method. Calculated results show good agreement. Numeral results are given for tees on partially filled rectangular waveguides.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 7, pp. 901–909, July, 1996.     

Electron and positron planar channeling radiation from diamond

Channeling-radiation spectra have been obtained from a diamond with ≈ 54.5 MeV electrons and positrons. Theoretical calculations are found to fit the experimental results well for electrons, but significant discrepancies exist between theoretical predictions and the positron data.     

Superconductivity in the platinum germanides MPt4Ge12 (M = rare-earth or alkaline-earth metal) with filled skutterudite structure

New germanium-platinum compounds with the filled-skutterudite crystal structure were synthesized. The crystal structure and composition were investigated by x-ray diffraction and microprobe analysis. Magnetic susceptibility, specific heat, and electrical resistivity measurements evidence superconductivity in LaPt4Ge12 and PrPt4Ge12 below 8.3 K. The parameters of the normal and superconducting states were established. Strong coupling and a crystal electric field singlet ground state is found for the Pr compound. Electronic structure calculations show a large density of states at the Fermi level. Similar behavior with lower Tc was observed for SrPt4Ge12 and BaPt4Ge12.     

Wave numbers of partially filled rectangular waveguide

An approximate method is proposed for determination of the wave numbers of a partially filled rec angular waveguide. The method employs the eigenvalues and parameters of Mathieu equations. The natural H-and E-waves of a partially filled rectangular waveguide are expressed in terms of Mathieu functions. Numerical results of waven number studies are presented and interpreted graphically.     

Eigenfunctions of a partially filled rectangular waveguide

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 12, pp. 1385–1390, December, 1990.     

Magnetic properties,electronic structure,and optical properties of the filled skutterudite BaFe4Sb12

The magnetic properties, electronic structure, and optical properties of the filled skutterudite BaFe₄Sb₁₂ are calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) plus local orbital method. It is found that the local spin density approximation (LSDA) method appears more accurate than the generalized gradient approximation (GGA) method in calculating the electronic structures and optical properties of this compound. Furthermore, our calculated lattice constant and spin magnetic moments with the LSDA method are in overall better agreement with experiment. In contrast with recent experiment, our calculations are in good agreement with experimental reflectivity spectra and optical conductivity spectrum.     

Metallic thin film depth measurements by X-ray microanalysis

In this study, a low-cost technique, energy dispersive spectroscopy (EDS), was used to explore the application of X-ray microanalysis in depth determination of metallic films. Al, Ni and Au films with varied thicknesses from 50 to 400 nm were deposited on silicon (Si) substrates by magnetron sputtering. Electron beam energies ranging from 4 to 30 keV were applied while other parameters were kept constant to determine the electron beam energy required to penetrate the films. The effect of the atomic number of the metallic films on the penetration capability of the electron beam was investigated. Based on the experimental results, mathematical models for Al, Ni and Au films were established and the interaction volume was simulated using a Monte Carlo program. The simulations are in good agreement with the experimental results. Al/Ni/Au multilayers were also studied.     

X-ray microanalysis of uterine epithelial cells in culture

The ionic composition of the uterine fluid, secreted by the endometrium, is of importance for fertilization and embryonic development. Little, however, is known about the ion transport mechanisms in the uterine epithelial cells. Because it is difficult to study ion transport in this tissue in situ, a method was developed to culture mouse uterine epithelial cells for X-ray microanalysis in the electron microscope, in order to allow the study of ion transport. Our data suggest the presence of a number of ion transport mechanisms in the cultured uterine epithelial cells. The cells appear to possess a ouabain-sensitive Na⁺---K⁺-ATPase, an amiloride-sensitive Na⁺---H⁺ antiporter, cAMP- and Ca²⁺-activated chloride channels, and volume-activated chloride efflux and influx mechanisms. In addition, chloride efflux can be stimulated by cholinergic and alpha-adrenergic agonists. Only a few of these mechanisms had been studied previously in the uterine epithelium.     

Anomalous X-ray scattering and channeling inside hollow microcapillary structures

XANES L _2,3 spectra and the reflection spectra of silicon, obtained in the case of the grazing incidence of radiation onto channel walls of microchannel plates, are studied. The channeling of secondary long-wavelength X-ray radiation was observed due to anomalous scattering in the vicinity of L edges of silicon absorption. The spectral composition of the secondary radiation at the microchannel output remains unchanged. The surfacebound propagation of X-ray fluorescence excited inside microchannels is observed for angles of incidence of less than θ ≈ θ_c/2.     

Optical properties of the filled skutterudite LaFe4P12

Full potential linearized augmented plane wave plus local orbital method (FPLAPW+lo) calculations were performed for LaFe₄P₁₂ in the filled skutterudite in order to investigate the optical properties and to show the origin of the different optical transitions. It is found that the band gap is indirect for LaFe₄P₁₂. Then the contribution of the different transitions peaks is analyzed from the imaginary part of the dielectric function. In contrast to recent experimental expectations, our calculations are in good agreement with experimental reflection spectra and ε₁(ω) spectrum.     

FP-LMTO calculations of elastic and electronic properties of the filled skutterudite CeRu4P12

First-principles calculations have been used to investigate the structural, electronic and elastic properties of the filled skutterudite CeRu₄P₁₂, using the full-potential linear muffin-tin orbital (FP-LMTO) method. The exchange-correlation energy is described in the local spin density approximation (LSDA) using the Perdew–Wang parameterization. The results of the electronic properties show that this compound is an indirect band gap material. A special interest has been made to the determination of the elastic constants since there have been no available experimental and theoretical data. The energy band gaps and their volume and pressure dependence are investigated. Our results of the ground-state electronic properties are found to agree with experimental results.