Positron annihilation probing of crystallization effects in TAS-235 glass affected by Ga additions

Crystallization effects in Te₂₀As₃₀Se₅₀ glass known also as TAS-235 affected by Ga additions to Ga₂Te₂₀As₂₈Se₅₀ and Ga₅Te₂₀As₂₅Se₅₀ compositions are probed with positron annihilation spectroscopy in the measuring modes exploring positron lifetimes and Doppler broadening of annihilation line. Occurring of cubic-phase Ga₂Se₃ droplets with character nanoscale sizes in partially-crystallized Ga₂Te₂₀As₂₈Se₅₀ alloy is shown to be associated with agglomeration of intrinsic free-volume voids, this process being enhanced over microcrystalline scale in Ga₅Te₂₀As₂₅Se₅₀ alloy. Crystallization changes in the void structure of TAS-235 glass are considered in terms of free-volume evolution under the same principal chemical environment responsible for positron trapping in amorphous and partially crystallized substances.     

Influence of silver on the galvanomagnetic properties and energy spectrum of mixed (Bi1− x Sbx)2Te3 crystals

An investigation is made of the temperature dependences of the resistivity in the range 4.2–300 K, the Hall effect, and the Shubnikov-de Haas effect in magnetic fields up to 40 T in (Bi_{1? x} Sb_x)₂Te₃Ag_y single crystals (0 ≤ x ≤ 0.75). Doping (Bi_{1? x} Sb_x)₂Te₃ crystals with silver showed that in Sb₂Te₃ and (Bi_{1? x} Sb_x)₂Te₃ crystals unlike Bi₂Te₃ silver exhibits acceptor properties. The angular and concentration dependences of the Shubnikov-de Haas effect were studied in (Bi_{1? x} Sb_x)₂Te₃Ag_y. It was established that the anisotropy of the ellipsoids of the upper valence band in Bi_0.5Sb_1.5Te₃ remains unchanged as a result of silver doping.     

Mössbauer study of the effect of preparation parameters in rapidly quenched Fe−Cr−P−C,Fe−Cr−B and Ni(57Fe)P amorphous alloys

Mössbauer spectroscopy was used to get information about the effect of preparation parameters (quenching rate, temperature and time of solution treatment of melt) on the structure of rapidly quenched Fe₇₀Cr₁₀C₇P₁₃, Fe₇₉Cr₁₅B₁₅ and Ni₈₀ ⁵⁷Fe₁P₁₉ amorphous alloys. We have found smaller but measurable thickness dependent changes in the average Mössbauer parameters and in the hyperfine field distribution of Fe₇₀Cr₁₀C₇P₁₃ samples than those observed in Fe₇₀Cr₁₀C₁₀P₁₀ amorphous alloys [3]. On the other hand, differences were found in the hyperfine field distribution of very rapidly quenched Fe₇₀Cr₁₀C₇P₁₃ alloys with increasing time of solution treatment of melt. Changes in the average parameters and in the quadrupole splitting distribution were also observed with variation of thickness as well as of temperature of melt in the Fe₇₀Cr₁₅B₁₅ and Ni₈₀(Fe)P₁₉ samples, respectively. The finding can be interpreted in terms of changes in the short range order due to different preparation conditions.     

Nb对C-15结构V2(HfZr)系列的超导转变温度的影响

本文中研究了C-15结构V₂Hf_1-xNb_x,V₂Zr_1-xNb_x和V₂Hf_0.5Zr_0.5-xNb_x系列的超导转变温度T_c与Nb合量x的关系,发现V₂Zr,V₂Hf加Nb后与V₂Hf_0.5Zr_0.5加Nb后性能显著不同。测定了V₂Zr,V₂Hf和V₂Hf_0.5Zr_0.5的X射线光电子能谱。结果表明,当Hf原子和Zr原子共存于AB₂化合物的A位上时,发生了一种增强原子间相互作用的新的电荷转移。这个事实支持由角动量分波表象能带论方法分析电声耦合超导原理的结果对四元V₂(HfZrNb)系列的超导行为提出的一种可能解释:4d-5d原子配位可能有助于提高4d导带的杂化程度,从而有利于提高超导T_c。 关键词：     

Infrared and Raman spectra and vibrational assignments of diiodomethane and its deuterated analogs

The infrared (from 4000 to 100 cm^?1) and Raman spectra of CH₂I₂ and CD₂I₂ have been recorded in the liquid and gaseous phases. Assignments have been made for all observed bands and, in the case of CH₂I₂, compared with those previously reported. Some bands appearing in the CD₂I₂ spectrum have been attributed to the presence of CHDI₂. The wavenumbers of the fundamental bands of CHDI₂ have been calculated from those of CH₂I₂ and CD₂I₂ using Brodersen and Langseth's rule, and compared with those observed in the CD₂I₂ spectrum.     

飞机跑道胶痕的自动识别系统设计与实现

为了减轻机场跑道除胶工作人员的劳动强度,提高除胶工作效率,文章提出了一种基于机器视觉的胶痕自动查找和识别方法,设计了基于ARM单片机控制的图像无线采集和基于PC机控制的图像接收、图像预处理和图像识别系统。文章通过分析预处理后的数据特点,确定了基于细胞神经网络算法的胶痕识别算法,然后在MATLAB仿真环境下确定了该算法的最优模型和参数,最后在Visual C++ 6.0环境下完成了该算法的程序编译,调试并完成了对胶痕的自动识别过程。理论仿真和程序测试的结果证明了文章提出的方法在胶痕自动识别系统中的可行性,也为机场特种设备的无人化和智能化提供了参考。     

J-aggregates of pseudoisocyanine with long alkyl substituents in thin films: Synthesis, spectral properties, and thermal stability

The formation and properties of J-aggregates in thin solid films of pseudoisocyanines with long N-alkyl groups, obtained by centrifuging from solutions in organic solvents, were studied. It is shown for the first time that nonsymmetric cyanine dyes, containing a C₂H₅ group at one nitrogen atom and a C₁₀H₂₁, C₁₅H₃₁, or C₁₈H₃₇ group at another nitrogen atom, spontaneously form J-aggregates stable at room temperature and pressing a narrow absorption band with a half-width at half maximum of 200 cm^?1. The thermal stability of J-aggregates in thin films of pseudoisocyanines with alkyl substituents decreases in the following order: C₂H₅-C₂H₅> C₂H₅-C₆H₁₃>C₂H₅-C₁₈H₃₇>C₂H₅-C₁₀H₂₁>C₂H₅-C₁₅H₃₁. By introducing 1-octadecyl-2-methylquinolinium iodide in the film, it was found that the J-aggregates studied consist of a small number (2–4) of dye molecules.     

Effect of absorbed hydrogen on magnetic behavior of Th7Co3 and Th7Ni3

The Pauli paramagnets Th₇Fe₃, Th₇Co₃ and Th₇Ni₃ become superconducting below 1.86 K, 1.83 K and 1.98 K, respectively. These compounds absorb large amounts of hydrogen to form the very hydrogen-rich phases Th₇Fe₃H₃₀, Th₇Co₃H₂₂ and Th₇Ni₃H₂₄. From magnetization studies it is found that hydrogenation results in an increase in the susceptibility of Th₇Co₃, and in a decrease in the susceptibility of Th₇Ni₃, but magnetic ordering is not observed in these two. This is in contrast to the behavior of Th₇Fe₃H₃₀ which is magnetically ordered with a Curie temperature above 350 K.     

Effect of WO3 on structural and optical properties of CeO2-PbO-B2O3 glasses

Pure and WO₃ doped CeO₂-PbO-B₂O₃ glasses are prepared by the melt-quench technique. The structural and optical analyses of glasses are carried out by XRD, FTIR, density and UV-vis spectroscopic measurement techniques. FTIR analysis indicates the transformation of structural units of BO₃ into BO₄ with W-O-W vibration and the presence of WO₄ and WO₆ units observed with increase in WO₃ contents. Decrease in band gap for CeO₂-PbO-B₂O₃ glasses from 2.89 to 2.30 eV and for WO₃ doped glasses from 2.89 to 1.95 eV has been observed and discussed. This decrease in band gap with WO₃ doping approaches to semiconductor behavior. It shows that the presence of WO₃ in the glass samples causes more compaction of the borate network due to the formation of BO₄ groups and the presence of WO₄ and WO₆ groups, which result in a decrease in the optical band gap energy and increase in the density.     

Intermediate valence of europium in EuxLa1−xBe13

Mössbauer studies of the 21.6 keV transition of¹⁵¹Eu in cubic EuBe₁₃ and Eu_1/2La_1/2Be₁₃ in the temperature range 100 K to 600 K have been performed. The position of the absorption line in EuBe₁₃ moves from 0.60 mm/s at 100 K to 0.04 mm/s at 575 K. In Eu_1/2La_1/2B₁₃ the line moves from 0.50 mm/s at 100 K to –0.03 mm/s at 500 K. We conclude that Eu in Eu_xLa_1–xB₁₃ is in an intermediate valence state and we analyze the temperature dependence of the isomer shift in terms of an interconfigurational fluctuation model. The model contains temperature independent parameters E_exc, the interconfiguration excitation energy, T_f, the valence fluctuation temperature, and S₃, the isomer shift of pure Eu³⁺ in EuBe₁₃. Assuming S₃–S₂= 13 mm/s the analysis yields S₃=0.70 mm/s, T_f=400 K and E_exc=3000 K for EuBe₁₃, whereas T_f=460 K and E_exc=2750 K for Eu_1/2La_1/2B₁₃.     

Solid state- and magneto-chemistry of the SrO-Fe2O3 system: III. The non-existence of single-phase “SrFe2O4”

A detailed Mössbauer investigation of 1 : 1 SrO : Fe₂O₃ has shown that a single phase with the SrFe₂O₄ composition does not exist in the SrO-Fe₂O₃ system when SrCo₃ and Fe₂O₃ are reacted in air. A multiphase assemblage of SrFe₁₂O₁₉, Sr₄Fe₆O₁₃, and SrFeO_3-x is observed in the material with an overall composition of “SrFe₂O₄”. By means of novel analyses of the complex Mössbauer spectra of the 1 : 1 SrO : Fe₂O₃ composition, all of the Fe containing phases have been identified and their respective mole percentages determined. The relative amounts of the phases present depend on the final firing temperature. The published X-ray powder data for “SrFe₂O₄” can be interpreted satisfactorilly in terms of the Mössbauer results, i.e., as a multiphase assemblage, and corresponds to a low temperature assemblage of SrFe₁₂O₁₉, Sr₄Fe₆O₁₃ and SrFeO_3-x for the overall composition of “SrFe₂O₄”.     

Structure and magnetic order in La0.7Ca0.3Mn0.5Co0.5O3 and La0.8Sr0.2Mn0.5Co0.5O3 perovskites

In this paper we report the study of the perovskites La_0.7Ca_0.3Mn_0.5Co_0.5O₃ and La_0.8Sr_0.2Mn_0.5Co_0.5O₃ by neutron powder diffraction at various temperatures and magnetization measurements in zero applied field and at low cooling regimes. The replacement of half Mn by Co in La_0.7Ca_0.3MnO₃ and La_0.8Sr_0.2MnO₃ destroys their long-range ferromagnetism exhibiting a cluster glass ferromagnetic order similar to the one observed in many cobaltites.     

Doping effect on crystal structure and conduction property of fast oxide ion conductor LaGaO3-based perovskite

In order to discuss oxide ion conduction mechanism for LaGaO₃-based perovskite compounds, doping effects were investigated using two kinds of solid solutions whose oxygen vacancy concentrations are the same: one is La_0.9Sr_0.1Ga_0.9Mg_0.1O_2.9 with A-site and B-site substitutions and the other is LaGa_0.8Mg_0.2O_2.9 with only B-site substitution. Conductivity measurements showed that La_0.9Sr_0.1Ga_0.9Mg_0.1O_2.9 had a circumstance whereby oxide ion could more easily diffuse in the perovskite structure than in LaGa_0.8Mg_0.2O_2.9. Structural analyses using neutron diffraction found out the following three differences: the first finding was that the saddle point formed by two A-site cations and one B-site cation in La_0.9Sr_0.1Ga_0.9Mg_0.1O_2.9 was larger than that in LaGa_0.8Mg_0.2O_2.9 due to larger displacements of A-site and B-site cations; the second was that the doubly doping with Sr and Mg was more effective for reduction of GaO₆ octahedral tilt angles than the doping with Mg; the last was that La_0.9Sr_0.1Ga_0.9Mg_0.1O_2.9 had larger oxygen displacement than LaGa_0.8Mg_0.2O_2.9. It was considered that these structurally related parameters dominated the high oxide ion conduction in LaGaO₃-based perovskite compounds.     

Raman spectra in hollandite type compounds K1.6Mg0.8Ti16 and K1.6Al1.6Ti6.4O16

Raman spectra of single crystals of one-dimensional superionic conductors K_1.6Mg_0.8Ti_7.2O₁₆ and K_1.6Al_1.6Ti_6.4O₁₆ have been measured. Both the spectra show very similar features one another. Raman peaks in K_1.6Mg_0.8Ti_7.2O₁₆ appear at low frequencies compared to corresponding Raman peaks in K_1.6Al_1.6Ti_6.4O₁₆. A qualitative interpretation of these spectra is examined in terms of a comparison with the Raman spectra of rutile and the factor group analysis.     

Infrared properties of AsχTe1−χ glasses

Infrared reflection and transmission measurements in As_χTe_1?χ glasses (45?×?55) show well-defined Gaussian vibrational absorption peaks. Comparisons with spectra observed in crystalline and glassy As₂S₃ and As₂Se₃ indicate that the local order in As_χTe_1?χ glasses is not like that found in crystalline As₂Te₃, but rather it consists primarily of AsTe₃ pyramids which are probably linked together in a fashion similar to that found in As₂S₃ and As₂Se₃.     

IR-Spectra of M2UO2F4.H2O Complexes

This work is devoted to the study of and Rb₂UO₂F₄.H₂O and Cs₂UO₂F₄. H₂O IR-spectra with the aim of obtaining a set of vibration frequencies characterising M₂U0₂F₄.H₂O complexe elucidating the role and nature of water bonds in the structures of the above-mentioned compounds; and receiving preliminary information on the structure of M₂UO₂F₄.H₂O. The investigated compounds were synthesized in accord with our previous paper¹. M₂UO₂D₂O and M₂UO₂F₄.HDO were obtained by recrystallizing M₂UO₂F₄.H₂O from D₂O and HDO respectively     

Energy Levels in the Forbidden Band of the Bi4Ge3O12 Ceramics

Thermally stimulated luminescence in the Bi₄Ge₃O₁₂ ceramics and also in the ceramics of the parent components Bi₂O₃ and GeO₂ is investigated. The similarity of the curves of the thermally stimulated luminescence in bismuth germanate with the structure of eulytine Bi₄Ge₃O₁₂ and sillenite Bi₁₂GeO₂₀ is explained. The relation of the thermally stimulated luminescence band in Bi₄Ge₃O₁₂ (with a maximum at 143 K) to the disruptions in the germanium sublattice and of the thermally stimulated band (with a maximum at 187 K) to the recombination processes in the bismuth sublattice is shown. It has been established that the light sum in the Bi₄Ge₃O₁₂ ceramics is stored most effectively upon excitation by light in an energy region of 4.4 eV.     

Structural features of liquid metallic glass former

The structural parameters of Au₇₅Si₂₅ alloy, pure Au, Al₈₈Si₁₂, Cu₈₇Sn₁₃, In₉₈Al₂ and Al₉₃Ni₇ alloys have been measured by X-ray diffractometer. It is found that there are subpeaks in the pair correlation functions in liquid Au₇₅Si₂₅ alloy. The addition of Si in liquid Au results in a decrease in both the correlation radius and the coordination number of the nearest atomic neighbors. The Au₇₅Si₂₅ alloy nearest atomic distance has a more stable dependence on temperature compared to In₉₈Al₂, Al₉₃Ni₇ and Cu₈₇Sn₁₃ alloys. The atomic density change of liquid Au₇₅Si₂₅ alloy is less dependent on temperature than the liquid Au and Al₈₈Si₁₂ alloy. The liquid metallic good glass former Au₇₅Si₂₅ alloy possesses a more stable liquid structure than that of poor glass formers, indicating the essential of the fragility of the superheated melts.     

Investigations of alkali doped Fe2O3--V2O5 catalysts by transmission and conversion electron Mössbauer spectroscopy

Fe₂O₃--V₂O₅ catalysts doped with Cs₂SO₄ (molar ratio: V:Fe:Cs=1:0.74:0.06) were found to be a rather inhomogeneous mixture of various crystalline and amorphous iron vanadate phases. After calcination in air the catalyst was divided into three different parts which were analyzed separately revealing the formation of FeVO₄ in the top and bottom fraction of the crucible and Fe₂V₄O₁₃ in the middle fraction. As compared to the well crystallized FeVO₄ reference sample, the quadrupole splittings of FeVO₄ in the Cs-doped catalysts were larger pointing to more distorted iron sites which were assumed to be responsible for high catalytic selectivities. In contrast, the quadrupole splittings of FeVO₄ in the less selective K- and Rb-doped Fe₂O₃--V₂O₅ catalysts were smaller. Additional components in the bottom fraction were also α-Fe₂O₃ and Fe_1-xS. As indicated by the CEMS spectra the latter is located preferentially on the surface of the catalyst particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Composition-dependent melting behaviour of NaxK55–x core–shell nanoalloys

Molecular dynamics simulations at constant temperature are performed to investigate melting-like transition in Na₁₃K₄₂, Na₁₉K₃₆ and Na₂₆K₂₉ nanoalloys using a second-moment-approximation tight-binding analytic potential to calculate the forces on the constituent atoms. A weighted histogram analysis method is employed to remove non-ergodicity issues due to the complex potential energy surface of these nanoalloys. The heat capacity shows three distinctive steps in melting for Na₁₃K₄₂, while Na₂₆K₂₉ and Na₁₉K₃₆ have two-step and one-step melting transition, respectively. The steepest descent method is used to quench the configurations in a given interval during the simulation and also study the isomerisation processes occurring at different temperatures. Analysing the configuration energies of quenched structures for the entire nanoalloy and the core atoms separately gives more details about the melting mechanism. The Lindemann parameter is also calculated at several temperatures during the simulation which shows a gradual increase for Na₁₃K₄₂ and Na₂₆K₂₉ while a sharp change is observed for Na₁₉K₃₆. These findings are in agreement with the multi-step nature of the phase transition in Na₁₃K₄₂ and Na₂₆K₂₉ and one-step melting of the Na₁₉K₃₆ magic composition.