深过冷Cu60Sn30Pb10偏晶合金的快速凝固

实现了大体积Cu₆₀Sn₃₀Pb₁₀偏晶合金的深过冷与快速凝固. 实验获得的最大过冷度为173 K(0.17T_L). 凝固组织发生了明显的宏观偏析,XRD分析表明,试样上部是由固溶体(Sn),(Pb)相和金属间化合物ε(Cu₃Sn)相组成的三相区,下部为富(Pb)相区. 在小过冷条件下,三相区中ε(Cu₃Sn)相的凝固组织为粗大的枝晶,随着过冷度的增大,ε(Cu₃Sn)相细化成层片状组织,且层片间距随过冷度的增大而减小,而(Sn),(Pb)两相始终以离异共晶的方式存在. 富(Pb)相区中分布有少量的ε(Cu₃Sn)枝晶,枝晶长度随过冷度的增大而增大,且在大过冷条件下发生碎断. (Sn)相在ε(Cu₃Sn)相表面形核、长大,其形态类似于包晶凝固组织. 关键词： 深过冷 快速凝固 偏晶合金 层片组织     

Is the Kβ/Kα x-ray intensity ratio dependent upon the energy of an inducing proton?

K_β/K_αX-ray intensity ratios have been measured for various elements between Z = 29 and Z = 79 for incident proton energies of 23.6, 32.1 and 43.6 MeV. The results yield no evidence for a variation in ratio with particle energy.     

High electronic specific heat of some cubic UX3 intermetallic compounds

The low temperature specific heat of cubic UX₃ intermetallic compounds with X = Al, Ga, In, Si, Ge and Sn have been measured. High values for the coefficient of the electronic specific heat have been found, ranging from 14 to 169 mJ/mol K².     

Magnetic properties of (Mn1 − x Fe x )1.68Sn solid solutions

Solid solutions in the (Mn_{1 ? x} Fe _x )_1.68Sn system (x ≤ 0.5) with a Ni₂In-type structure are synthesized by the solid-phase reaction method in a stepwise temperature regime. The unit cell parameters a and c decrease with an increase in the iron concentration in the alloys and become equal to a = 0.430 nm and c = 0.538 nm for the (Mn_0.5Fe_0.5)_1.68Sn alloy. A superstructure with the unit cell parameters a _ss = 3a and c _ss = c is revealed in alloys of the system under investigation. The specific magnetization of the alloys increases nonlinearly from 53 G cm³ g^?1 in the Mn_1.68Sn alloy to 72 G cm³ g^?1 in the (Mn_0.5Fe_0.5)_1.68Sn solid solution. The Curie temperature changes from 270 K in the initial alloy of the composition Mn_1.68Sn to 365 K in the alloy of the composition (Mn_0.5Fe_0.5)_1.68Sn. All solid solutions in the (Mn_{1 ? x} Fe _x )_1.68Sn (x ≤ 0.5) system exhibit metallic conductivity in the temperature range from 77 to 450 K.     

Mechanochemical synthesis in the Ni-Al-C system

Specific features of the phase formation during mechanochemical synthesis of mixtures of elementary components, Ni, Al, and graphite, in an atomic ratio of 2:1:1 and a mixture of the intermetallic compound Ni₃Al and graphite (1:1) have been considered. It is shown that nanocrystalline (D = 4–6 nm) three-component solid solutions Ni(Al, C) with identical lattice constants (a = 0.366 nm) are formed during mechanosynthesis, independent of the initial components. Annealing at a temperature of 800°C for 2 h leads to decomposition of solid solutions into three phases: double carbide Ni₃AlC_0.46 (a = 0.3592 nm), solid solution Ni(Al, C) with the lattice constant 0.3546 nm, and graphite with the lattice constants a = 0.2461 nm and c = 0.660 nm.     

Characterization of dip-coated ITO films derived from nanoparticles synthesized by␣low-pressure spray pyrolysis

In₂O₃:Sn (Indium Tin Oxide; ITO) films were prepared from a sol solution with highly crystalline ITO nanoparticles (less than 20 nm in size with 10 at.% Sn) which had been prepared by low-pressure spray pyrolysis (LPSP) in a single step. The ITO sol solution was prepared by dispersing LPSP-prepared ITO nanoparticles into ultra pure water. The nanoparticle ITO film was deposited on a glass substrate using a dip-coating method and then annealed in air at various temperatures. The optical transmittances of the ITO films were measured by UV–Vis spectrometry, and the films were found to have a high transparency to visible light (in the case of a film thickness of 250 nm annealed at 400°C, the transparency was in excess of 95% over the range λ=450–800 nm, with a maximum value near 100% at wavelengths above λ=700 nm). The optical transmittances of the films were influenced by the size of the ITO particle used, the film thickness and the annealing temperature. The ITO films showed a minimum resistivity of 9.5×10⁻² Ω cm, and their resistivity was affected by both the ITO particle size and the annealing temperature used.     

119Sn Mössbauer spectroscopy: a powerful tool to unfold the reaction mechanism in advanced electrodes for lithium-ion batteries

Cobalt–tin intermetallic compounds with different particle size have been obtained and characterized by using ¹¹⁹Sn Mössbauer spectroscopy as a main tool. The electrochemical behavior of the Co–Sn compounds has been evaluated in lithium test cells. The Lamb–Mössbauer factors for CoSn with different crystallite sizes have been calculated. The results f _nano???CoSn(300 K) = 0.19 and f _{coarse???CoSn}(300 K) = 0.55 are obtained. Nano-CoSn exhibits larger capacity to react with lithium than coarse-CoSn.     

VUV luminescence of Er<Superscript>3+</Superscript> ions in LiYF<Subscript>4</Subscript> and BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals

Vacuum ultraviolet luminescence of Er³⁺ ions in LiYF4 and BaY₂F₈ crystals has been investigated. It is revealed that under excitation by 193 nm radiation from an ArF excimer laser the interconfigurational 5d–4f radiative transitions in Er³⁺ ions are observed. It is shown that from the LiYF₄:Er crystal only the spin-forbidden luminescence (λ = 165 nm) is detected, whereas both the spin-forbidden (λ = 169 nm) and spin-allowed (λ = 160.5 nm) components are observed from the BaY₂F₈:Er crystal.     

Generation of characteristic x rays by a terawatt femtosecond chromium-forsterite laser

Characteristic K _α x rays arising when a metallic target is irradiated by femtosecond infrared pulses that are generated by a terawatt chromium-forsterite laser system (1240 nm, 90 mJ, 80 fs) are studied. The absolute yield (up to 3 × 10⁸ photons/sr pulse) and the coefficient of the transformation of laser radiation to K _α radiation (maximum value ≈0.03%) are measured for an iron target. The dependence of the radiation intensity on the angle of incidence of p polarized laser radiation is analyzed. The mechanisms of the production of fast electrons responsible for generating characteristic x rays are discussed.     

Crystal Structure of the Intermetallic Thin-Film Cu–Sn Condensate

The synthesis of intermetallic compounds in multilayer Cu–Sn films is confined within reaction islands, which can attain 100 nm in size. X-ray diffraction analysis reveals the predominance of one intermetallic Cu₆Sn₅ phase, while electron microscopy evidences a high crystallographic orientation of its islands. They have the same orientation to the film surface, but are rotated with respect to each other at different angles and randomly oriented to the axis, which is perpendicular to the film plane and coincide with the crystallographic axis [100] of individual single crystals.     

Phase transition and proton exchange in 1,3-diazinium hydrogen chloranilate monohydrate

In the hydrate crystal of 1:1 salt with 1,3-diazine and chloranilic acid (H₂ca), (1,3-diazineH)·H₂O·Hca, an unique hydrogen-bonded molecular aggregate is formed. There exists proton disorder in the N–H...O hydrogen bond between 1,3-diazinium ion and water (H₂O) of crystallization. In order to reveal dynamic aspect of this disorder, ³⁵Cl NQR measurements were conducted. Two resonance lines observed at 35.973 and 35.449 MHz at 321 K split into four lines below T _c?=?198 K clearly showing occurrence of a solid–solid phase transition; 36.565, 36.357, 36.011, 35.974 MHz at 77 K. Temperature dependence of spin-lattice relaxation time T ₁ in high-temperature phase was observed to obey an Arrhenius-type relation with the activation energy of 8.5 kJ mol^???1. This result leads to the conclusion that proton exchange in the N–H...O hydrogen bond takes place in the high-temperature phase. Specific heat measurements by DSC resulted in the transition entropy ΔS?=?1.3 J K^???1 per 1 mole [(1,3-diazineH)·H₂O·Hca]₂ which is far less than 2R ln2 = 11.5 J K^???1 mol^???1. It is expected that proton exchange in the two hydrogen bonds within the aggregate does not occur independently but concertedly with strong correlation in the high-temperature phase.     

Absorption by XeCl* excimer molecules of their own emission of the В–Х transition (λ = 308 nm) in a dense Ar–Xe–CCl<Subscript>4</Subscript> medium upon pumping by fast electrons and uranium-235 fission fragments

Luminescence of dense Ar–Xe–CCl₄ gas mixtures with a low CCl₄ content upon pumping by fast electrons and uranium-235 fission fragments is studied by spectroscopic methods. It is found that, in a cell with a resonator tuned to the В–Х transition of the XeCl* molecule (λ = 308 nm), the D-state population of the XeCl* excimer molecule (the D–X transition, λ = 235 nm) depends on the B-state population and increases by many times with increasing B-state population of the XeCl* molecule. The stimulated absorption coefficient k = 1.2 × 10^–16 of В–Х transition emission of the XeCl* molecule (λ_max = 308 nm), which leads to population of the D-state of this molecule, and the coefficient of amplification μ = 2.5 × 10^–4 cm^–1 of В–Х transition emission of the ХеCl* molecule (λ = 308 nm) are measured upon pumping by uranium- 235 fission fragments with the specific energy input into the gas medium of ~60 mJ/cm³ and a specific power of energy input of about 240 W/cm³.     

Determination of the K-shell internal conversion coefficient for the 37.2 keV transition in the decay of121mSn

TheK-shell internal conversion coefficientα _K for the 37.2 keV transition (7/2⁺→5/2⁺) occuring in¹²¹Sb afterβ ^? decay of¹²¹ mSn has been redetermined applying theX- toγ-peak method (XPG). Measurements of photon spectra from thin sources have been performed at various source-detector distances with a high resolution, efficiency calibrated Si(Li) detector. Values ofα _K have been deduced from the number of emittedKX rays compared to that of the emittedγ rays. TheK-shell fluorescence yield for antimony has been taken from the literature. From in total 14 experimental runs a mean result ofα _K =9.52±0.27 has been obtained. The quoted uncertainty comprising statistical and systematic parts is discussed in detail. The present result is compared with the few existing earlier experimental values and with the theoretical value interpolated from the most recent tabulations.     

Effet Mössbauer sur les noyaux d'impuretes 119Sn4+ dans la matrice de VO2

The phase transition in VO₂ doped with 0.16 at.% Sn⁴⁺ was investigated by Mössbauer spectroscopy of ¹¹⁹Sn. Hyperfine magnetic fields were observed on ¹¹⁹Sn nuclei below the transition temperature. At 77 K the maximum hyperfine magnetic field was found to be H(0)_{77 K} = 120 ± 10 kOe The results obtained are discussed in terms of fine antiferromagnetic particles.     

Nanocrystalline CoSn2-carbon composite electrode prepared by using sonochemistry

A sonochemical method has been used to prepare negative electrode materials containing intermetallic nanoparticles and polyacrylonitrile (PAN). The ultrasound irradiation is applied to achieve small particle size. After annealing at 490 °C under Ar-flow, the polymer PAN is partially carbonized and the metallic nanoparticles are surrounded by a carbonaceous matrix. The main metallic phase is CoSn₂. The carbonaceous coating and the surface oxides have been explored by using XPS. The resulting CoSn₂-carbonaceous phase electrode (CoSn₂@C) shows improved electrochemical behavior (ca. 450 mAh/g after 50 cycles) in comparison with previous reports on pure crystalline CoSn₂. The reaction between CoSn₂@C and Li has been studied by using XRD and ¹¹⁹Sn Mössbauer spectroscopy. The formation of large grains of crystalline Li_xSn phases after the first discharge is discarded. The small particle size which is achieved by using ultrasonication and the carbonaceous matrix contribute to maintain the Co-Sn interactions during the electrochemical cycling. The aggregation of the nanosized metallic particles upon electrochemical cycling can be suppressed by the carbonaceous matrix (pyrolytic PAN).     

Electric field gradient in nanostructured SnO2 studied by means of PAC spectroscopy using 111Cd or 181Ta as probe nuclei

Electric quadrupole interactions were studied in pure and Mn-doped powder samples and thin films of SnO₂ using perturbed γγ angular correlation spectroscopy (PAC). The powder samples were prepared by Sol gel method and the thin film were prepared on the Si (100) substrate by sputtering technique using Sn in the oxygen atmosphere. The samples were characterized by x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The thickness of the film was 100 nm. The average particle size of the SnO₂ powder samples was determined to be smaller than 60 nm. The radioactive ¹¹¹In and ¹⁸¹Hf tracers were introduced in the powder samples during the sol gel chemical process. Radioactive ¹¹¹In was implanted on the SnO₂ thin films using the University of Bonn ion implanter (BONIS). PAC measurements were carried out in a four BaF₂ detector spectrometer in the temperature range of 77–973 K for samples annealed at different temperatures. The PAC results for both nuclear probes show the presence of two electric quadrupole interactions. The major fractions in both cases correspond to the substitutional sites in the rutile phase of SnO₂. The results are compared with previous PAC measurements.     

The 120Sn(α, p)123Sb reaction in a semi-microscopic description

The three-nucleon stripping reaction ¹²⁰Sn(α, p)¹²³Sb is described in a semi-microscopic model in which only J^π = 0^? coupled neutron pairs are included. This spectator model describes the differences in excitation strengths of the (α, p) and (³He, d) reaction if the coupling between the transferred proton and the di-neutron is correctly taken into account.     

Effective production of Xe<Subscript>2</Subscript>I excimer molecules by high-energy charged particles in Xe containing a small amount of C<Subscript>3</Subscript>F<Subscript>7</Subscript>I

An anomalously high efficiency of generating Xe₂I* excimer molecules in dense Xe–C₃F₇I gaseous mixtures with a small amount of C₃F₇I that are excited by a pulsed beam of fast electrons is discovered. The electron energy is 150 keV, and the beam current amplitude and duration are, respectively, 5 A and 5 ns. The temporal–spectral characteristics of spontaneous radiation from XeI* and Xe2I* excimer molecules are measured. Also, the luminescence times of the upper level for the B–X transition in the XeI* molecule (λ_max = 253 nm) and the upper level for the 4²Γ–1²Γ transition in the Xe₂I* molecule (λ = 352 nm), as well as the rate constants of quenching these levels by the gaseous mixture components, are determined. Based on the characteristics of the track structure of a high-energy plasma produced by charged particles in the dense gaseous medium, a model of plasma-chemical processes leading to the formation of XeI* (λ_max = 253 nm) and Xe₂I* (λ = 352 nmnm) excimer molecules in a Xe–C₃F₇I mixture with a small amount of an iodine atom donor is suggested.     

Quadrupole interactions at 57Fe and 119Sn in 3d-metal antimonides

3d-metal antimonides: Fe_1+x Sb, N_+x Sb, Co_+x Sb and the (Ni_1?y Fe _y )Sb solid solution have been studied by the Mössbauer effect method at ⁵⁷Fe and ¹¹⁹Sn. It was found that the quadrupole interactions at the Fe and Sn nucleus in 3d-metal antimonides are very sensitive to the filling of different crystallographic sites with metal atoms. The metal atoms in trigonal-bipyramidal sites have a strong effect on the quadrupole splitting of ¹¹⁹Sn. They are nearest to anions (Sb or Sn) with the typical axial ratio of c/a = 1.25. The QS(x) dependence of ¹¹⁹ Sn in 3d-metal antimonides in the 0 ≤ x ≤ 0.1 concentration range can be used to determine x – the concentration of transition metal excess relative to the stoichiometric composition.     

Oxygen-phase-state changes in ZnS single crystals annealed in vapors of the constituents

Exciton reflection and emission spectra and edge emission have been investigated in ZnS sinle crystals grown from the melt and containing oxygen and then subjected to annealing in vapors of the constituents. The study of optical properties of the crystals cooled to 77°K were conducted in parallel with structural investigations of the crystals using proton and x-ray diffraction analyses. Based on the experimental data it was concluded that in the ZnS lattice, oxygen exists in a number of phase states: as part of a ZnS·O solid solution in the host lattice; as a precipitate from the saturated solid solutionβ=ZnS·O_sat; as an impurity atmosphere in the vicinity of packing faults; as ZnO precipitated on dislocations. The effect of oxygen in these various phase states on the exciton spectra and edge emission of ZnS was investigated. It was shown that oxygen is not very mobile in ZnS crystals annealed in sulfur vapor and it becomes concentrated mainly at packing defects. This leads to an increase in the concentration of packing defects and makes possible a transition from the cubic to the hexagonal modification of ZnS. The concentration of oxygen at packing defects leads to the appearance in reflection spectra and in the edge emission spectra ofα-ZnS of an additional hexagonal band located on the long wavelength side which is caused by the formation ofβ-ZnS·O solid solution. Oxygen diffuses quite rapidly through ZnS which has been annealed in zinc vapor and it precipitates from the crystals as the distinct phases ZnO orβ-ZnS · O_sat, and as a result the defect content of the hostα-ZnS lattice decreases. The concentration of the ZnO-phase is quite small and its exciton bands do not appear in the reflection spectra. The precipitation of the solid solution in the form of the phaseβ-ZnS · O_sat leads to the appearance of an additional long wavelength absorption edge in the 334 to 335 nm region (at 77°K). In addition, because single crystals of ZnS annealed in zinc vapor contain a large concentration of sulfur vacancies, there occurs a rather rapid formation of the solid solution on the layers ofα-ZnS close to the surface; this leads to a broadening and a shift toward longer wavelengths of the sphalerite exciton spectra. A similar shift is observed for the edge emission band ofα-ZnS. When the crystals are aged, theα-ZnS·O solid solution decomposes and the bands assume the standard sphalerite positions. Changes in the intensity of edge and exciton emission were investigated taking into account changes in the phase state of oxygen in the crystals.