Effect of proton and laser irradiation on the elastic and inelastic properties of a V-Ti-Cr alloy

The behavior of Young’s modulus E and the decrement of ultrasonic vibrations δ in a V-4Ti-4Cr alloy is studied during proton (8-MeV protons, dose rate 10⁴ Gy/s) or IR laser (YAG: Nd³⁺ laser, wavelength 1.06 μm, intensity up to 10² W/cm²) irradiation. Measurements are performed using the method of a composite piezoelectric oscillator (longitudinal 100-kHz resonance vibrations). The sizes of the irradiated surface regions of a sample in the proton and laser experiments are the same in order to provide the same thermal conditions in the sample-quartz transducer system. The amplitude, time, and temperature dependences of E and δ are measured before and after preliminary plastic deformation, as well as before, during, and after irradiation of a sample. The process of postdeformation aging (the kinetics of recovery of internal friction after deformation) during proton irradiation is shown to differ substantially from that during laser irradiation. The specific features detected can be explained by the more intense evolution of the defect structure during proton irradiation. Analysis shows that radiation annealing is related to the ionizing component of proton irradiation, which excites the electronic subsystem of the metallic alloy and, thus, creates hot electrons and plasmons. The electron excitations relax at lattice defects (dislocations) and increase the dislocation mobility; this results in a relatively rapid decrease in the dislocation density and in a more significant (as compared to the laser irradiation) decrease in the level of internal stresses in the material. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 8, 2004, pp. 1409–1415. Original Russian Text Copyright ? 2004 by Kardashev, Plaksin, Stepanov, Chernov.     

微型样品局部弹性的声显微成象研究

对微型样品或微掺杂复合材料样品的声学和机械特性进行了声显微成象研究,利用扫描声学显微镜对陶瓷基体内掺杂氮化硼纤维的复合材料进行了研究,在单根纤维内和基体中纤维-基体界面附近出现一系列明暗相间的圆环,分析了其形成机理,它是由于声显微镜输出信号中漏泄瑞利表面波信号同从纤维-基体界面反射的漏泄瑞利表面波信号之间相互干涉的结果。通过对干涉环的分析和研究,可求出瑞利波的声速,由此对微型样品的声学特性、弹性特性和力学性质进行研究和评价。     

The elastic and optical properties of the high-pressure hydrous phase δ-AlOOH

δ-AlOOH has recently been reported to be the least compressible hydrous phase known with a compressibility comparable to corundum and stishovite. It is predicted to be stable at the lower mantle conditions of the earth. By means of first principles methods, we have studied phase stability, electronic structure, elastic and optical properties of δ-AlOOH. Comparison between the elastic constants of δ-AlOOH and α-Al₂O₃ (corundum) shows that δ-AlOOH is as hard as corundum even though it contains 15% amount of water. In addition, δ-AlOOH has a calculated refractive index n similar to that of corundum.     

Characterisation of the high-pressure structural transition and elastic properties in boron arsenic

This paper carries out the First principles calculation of the crystal structures (zinc blende (B3) and rocksalt (B1)) and phase transition of boron arsenic (BAs) based on the density-functional theory. Using the relation between enthalpy and pressure, it finds that the transition phase from the B3 structural to the B1 structural occurs at the pressure of 113.42GPa. Then the elastic constants C₁₁, C₁₂, C₄₄, bulk modulus, shear modulus, Young modulus, anisotropy factor, Kleinman parameter and Poisson ratio are discussed in detail for two polymorphs of BAs. The results of the structural parameters and elastic properties in B3 structure are in good agreement with the available theoretical and experimental values.     

Optical properties of metal-polymer nanocomposites based on iron and high-pressure polyethylene

The optical reflectance and absorption spectra of nanocomposite materials based on iron and highpressure polyethylene (with different percentages of iron) were measured at room temperature in the visible and near-infrared regions. Oscillations of the absorption coefficient related to the optical transitions between minibands of the quantum well are revealed in the electronic spectrum of a metal nanoparticle. The experimental and theoretical data on the absorption coefficient are compared. It is shown that, with an increase in the iron concentration in the dielectric matrix, the discrepancy in the theoretical and experimental results decreases significantly.     

Structure-mediated transition in the behavior of elastic and inelastic properties of beach tree bio-carbon

Microstructural characteristics and amplitude dependences of the Young modulus E and of internal friction (logarithmic decrement δ) of bio-carbon matrices prepared from beech tree wood at different carbonization temperatures T _carb ranging from 600 to 1600°C have been studied. The dependences E(T _carb) and δ(T _carb) thus obtained revealed two linear regions of increase of the Young modulus and of decrease of the decrement with increasing carbonization temperature, namely, ΔE ～ AΔT _carb and Δδ ～ BΔT _carb, with A ≈ 13.4 MPa/K and B ≈ ?2.2 × 10^?6 K^?1 for T _carb < 1000°C and A ≈ 2.5 MPa/K and B ≈ ?3.0 × 10^?7 K^?1 for T _carb > 1000°C. The transition observed in the behavior of E(T _carb) and δ(T _carb) at T _carb = 900–1000°C can be assigned to a change of sample microstructure, more specifically, a change in the ratio of the fractions of the amorphous matrix and of the nanocrystalline phase. For T _carb < 1000°C, the elastic properties are governed primarily by the amorphous matrix, whereas for T _carb > 1000°C the nanocrystalline phase plays the dominant part. The structurally induced transition in the behavior of the elastic and microplastic characteristics at a temperature close to 1000°C correlates with the variation of the physical properties, such as electrical conductivity, thermal conductivity, and thermopower, reported in the literature.     

On the elastic and inelastic scattering of O

Elastic and inelastic scattering data on ¹⁷O on ⁴⁰Ca measured at E_1ab=61 MeV are analyzed using collective core contributions plus valence terms which are obtained with the microscopic single-folding model. The role of two-step transfers and reorientation processes is also assessed.     

An experimental study of He elastic,inelastic and charge-exchange scattering from Li

A target of ⁶Li was bombarded with the ³He beam from the University of Illinois cyclotron. Differential cross sections for the elastic scattering, the inelastic scattering to the first two excited states of ⁶Li, and the (³He, t) charge-exchange reaction to the ground state of ⁶Be were determined over angular ranges of approximately 20° to 115° (c.m.) at ³He energies of 24.6 MeV and 27.0 MeV. (The weak inelastic transition to the 3.56 MeV state of ⁶Li, ordinarily obscured by a background of three-body break-up, was observed by requiring a coincidence at most angles between the scattered ³He and the ⁶Li recoil.) The ratio of the integrated charge-exchange cross section between 55° and 115° to the integrated inelastic cross section for this transition (both with ΔT = 1) is somewhat less than expected from isospin considerations (i.e., about 1.6 instead of 2.0).     

Thermodielectric properties of polymer composites based on CuO-covered Cu particles in high-pressure polyethylene

An artificial nanocomposite medium made by embedding copper nanoparticles covered by copper oxide in a high-pressure polyethylene matrix is studied. Pioneering experiments are reported aimed at finding the temperature dependences of its insulating properties, dielectric relaxation time, and activation energy for polarization relaxation. The measurements are taken at a variable signal applied to the composite.     

Microstructure,elastic, and inelastic properties of biomorphic carbons carbonized using a Fe-containing catalyst

The microstructure and amplitude dependences of the Young’s modulus E and internal friction (logarithmic decrement δ), and microplastic properties of biocarbon matrices BE-C(Fe) obtained by beech tree carbonization at temperatures T _carb = 850–1600°C in the presence of an iron-containing catalyst are studied. By X-ray diffraction analysis and transmission electron microscopy, it is shown that the use of Fe-catalyst during carbonization with T _carb ≥ 1000°C leads to the appearance of a bulk graphite phase in the form of nanoscale bulk graphite inclusions in a quasi-amorphous matrix, whose volume fraction and size increase with T _carb. The correlation of the obtained dependences E(Т _carb) and δ(T _carb) with microstructure evolution with increasing Т _carb is revealed. It is found that E is mainly defined by a crystalline phase fraction in the amorphous matrix, i.e., a nanocrystalline phase at Т _carb < 1150°C and a bulk graphite phase at T _carb > 1300°C. Maximum values E = 10–12 GPa are achieved for samples with Т _carb ≈ 1150 and 1600°C. It is shown that the microplasticity manifest itself only in biocarbons with T _carb ≥ 1300°C (upon reaching a significant volume of the graphite phase); in this case, the conditional microyield stress decreases with increasing total volume of introduced mesoporosity (free surface area).     

Polarization effects for elastic and inelastic scattering with an adiabatic-propagator approximation

The effective coupling potentials derived from Feshbach's projection formalism can be significantly simplified with an adiabatic approximation in the propagator. For the diagonal and non-diagonal correction terms we derive perturbation series that lead to prominent shifts in both excitation energies and transition probabilities. We give a comparison between the conventional DWBA treatment and our modified analysis for¹⁶O+¹⁶O scattering.     

Theory of inelastic tunneling spectroscopy of a single molecule - Competition between elastic and inelastic current

A theory of inelastic electron tunneling spectroscopy of a single molecule with scanning tunneling microscope is presented using the Keldysh Green’s function method for an adsorbate-induced resonance coupled to the molecular vibration. It is found that the correction to the tunneling current is expressed in terms of the transmission probability; the correction is negative for the elastic part of the current and positive for the inelastic one. The differential conductance (dI/dV) exhibits an increase or decrease at the threshold corresponding to the opening of inelastic channel depending on the sign of the correction, and the size of this conductance jump is scaled with the vibrational damping due to electron-hole pair excitation. The lineshape of d²I/dV²-spectra calculated using a renormalized adsorbate Green’s function evolves from an antisymmetric dip to a peak through the derivative-like one as the position of the adsorbate resonance recedes from the Fermi level of the substrate.     

First principles study on the structural and optical properties of the high-pressure ZnO phases

A new high-pressure tetragonal phase (B10) of ZnO is investigated with an ab initio calculation based on density functional theory and is compared with the cubic B1 (rocksalt structure) and B2 (CsCl structure) phases at high pressure. It is found that the B10 phase has a more covalent nature than the B2 phase. The B1, B2, and B10 phases are semiconductors and their band gap energies are determined to be 3.73, 3.15, and 3.27 eV, respectively. The B10 phase has a similar optical response to the B2 phase, but not the B1 phase. The similarity of dielectric function between B10 and B2 phases are the result of the similar profiles of electronic density of state.     

On the elastic and inelastic S,P and D phase-shift analysis

An analytical method to find S, P and D phase shifts with and without absorption effects is presented. The method was tested in the π?N scattering case using experimental data at energies of 523 and 310 MeV. In the inelastic case it was found that there are three sets of $\text{T =}\text{3}\text{2}$ solutions consistent with the input data.     

Anomalous behavior of the elastic and inelastic properties in the ferroelectric phase of single-crystal (NH4)2SO4

The anomalous changes of the low-frequency elastic and inelastic properties of single-crystal (NH₄)₂SO₄ accompanying the phase transition from the paraelectric to the ferroelectric phase have been studied by the reverse torsion-pendulum method at 223 K and in the temperature region where the spontaneous polarization changes sign. Fiz. Tverd. Tela (St. Petersburg) 40, 2202–2205 (December 1998)     

聚乙烯冲击压缩特性实验研究

利用神光Ⅱ装置第九路输出的倍频激光,采用直接驱动方式研究了聚乙烯(CH₂)材料的冲击压缩特性.实验表明聚乙烯冲击波阵面自发辐射较强,冲击波在聚乙烯台阶中的传播比较稳定.采用阻抗匹配方法,以铝作标准材料,测量了聚乙烯的冲击绝热线,聚乙烯冲击压强达0.54 TPa,冲击波速度测量相对扩展不确定度~2%(K=2),实验数据的一致性较好,与已有低压实验数据及状态方程解析模型比较符合. 关键词： 聚乙烯 冲击绝热线 自发辐射 倍频激光     

Structure and deformation of polyethylene hard elastic fibers

Stress-strain and relaxation tests were performed in air between—196°C and +80°C, and in methanol and silicone oil at room temperature on linear polyethylene hard elastic fibers. Transmission electron microscope observations of similarly deformed specimens indicated that straining resulted in fibrils connecting separated lamellae. A new model was developed in order to rectify deficiencies which were exposed in existing models by our experimental results. The model attributes the stress for extension to the pulling of fibrils from lamellae and the retractive forces resulting in the particular elastic properties to surface energy and entropy effects in the fibrils.     

First-principles study of the optical properties of BeO in its ambient and high-pressure phases

Optical properties such as the dynamic dielectric function, reflectance, and energy-loss function of beryllium oxide (BeO) in its ambient and high-pressure phases are reported for a wide energy range of 0-50 eV. The calculations of optical properties employ first-principles methods based on all-electron density functional theory together with sum over states and finite-field methods. Our results show subtle differences in the calculated optical properties of the wurtzite, zincblende, rocksalt and CsCl phases of BeO, which may be attributed to the higher symmetry and packing density of these phases. For the wurtzite phase, the calculated band gap of 10.4 eV corresponds well with the experimental value of 10.6 eV and the calculated (average) index of refraction of 1.70 shows excellent agreement with the experimental value of 1.72.