Effect of plastic deformation and quenching on the absolute thermal emf of nickel

The effect of the degree and rate of plastic deformation of nickel on the change of its absolute thermal emf was studied. The dynamic effect of the change of thermal emf was established, the dynamic coefficient being 1.22–1.25. Plastic deformation of quenched nickel reduced its absolute thermal emf, on the basis of which conclusions are drawn about the contributions, different in sign, of holes and dislocations to the change of the absolute thermal emf of nickel. The kinetics were studied of the recovery of the thermal emf induced in nickel by plastic deformation, and the existence was established of two stages of recovery, differing in nature and with different activation energies, 0.1 and 0.3 eV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 77–81, June, 1971.     

Anomalies in transport properties in a magnetically ordered region on a Kondo lattice

The temperature dependences of resistivity and thermal emf on a Kondo lattice are calculated using the spin-polaron approximation. The peaks and sign reversal points of thermal emf as a function of temperature and concentration below the temperature of the transition to the paramagnetic state are determined. The concentration region containing the metal-insulator transition below the Curie temperature and the shift of the upper spin-polaron band are calculated.     

Anisotropy of the heat conduction,thermal emf,and Lorentz number in degenerate semimetals at low temperatures

The anisotropy of the heat conduction, thermal emf, and Lorentz number of degenerate semimetals at low temperatures, whose carriers possess an anisotropic energy spectrum, is investigated. It is shown that the anisotropy of heat conduction decreases with the reduction in temperature. At ultralow temperatures the diffusion thermal emf decreases proportionately to the temperature. The insignificant anisotropy of the thermal emf is due to the inelasticity of the electron collision.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 50–53, July, 1979.     

Bending induced rippling and twisting of multiwalled carbon nanotubes

We report that a twisting deformation mode emerges with the rippling in bent multiwalled carbon nanotubes via atomistic simulations. This mode arises from the curvature-induced lattice mismatch, and is energetically favorable. For the nanotubes with larger radii, twisting may enhance the local strain relaxation. Under the thermal fluctuation, the nucleation of defects involves bond breaking and reconstruction due to strain localization. The defective inner tubes undergo the cyclic torsion, resulting in unstable necking and even failure. Prior to fracture, a monatomic chain is formed under the combination of bending and twisting.     

石墨烯纳米带能带结构及透射特性的扭曲效应

利用基于密度泛函理论的第一性原理方法, 系统研究了石墨烯纳米带(GNRs)电学性质的扭曲效应. 结果表明: 锯齿型石墨纳米带(ZGNRs)的带隙对扭曲形变最不敏感, 在扭曲过程中几乎保持金属性不变, 其次是W=3p-1型扶手椅型石墨烯纳米带(AGNRs), 扭曲时带隙也只有较小的变化. W=3p+1型AGNRs的带隙对扭曲最为敏感, 扭曲发生时, 呈现宽带隙半导体、中等带隙半导体、准金属、金属的变化, 其次是W=3p型AGNRs, 扭曲时带隙变化也较为明显. 换言之, GNRs在无扭曲时带隙越大, 扭曲发生后带隙变化(变小)越明显. 对于整个电子结构及透射系数来说, 扭曲对AGNRs影响较大, 而对ZGNRs的影响相对小些. 研究表明: 由于石墨烯容易变形, 其相关电子器件的设计必须适当考虑扭曲对电学性质的影响.     

Structure of rectifying barrier in metal-gallium arsenide point contact

The measured volt-ampere and volt-capacitance characteristics, together with the thermal emf of the point contact, form the basis for a discussion of possible models of the rectifying barrier in a contact between metal and electronic gallium arsenide prior to, and at various stages in, electric forming.Prior to forming, current is rectified at the p-n junction in the surface region of the semiconductor. Contact properties do not depend on the metal used. The initial forming pulses destroy the surface film and produce either a Schottky barrier or an abrupt microalloy-type p-n junction. As the forming current increases, diffusion processes play an ever greater role, and a p-n junction with smoothly distributed impurities is created.     

Structure of the 3d-band and thermal emf of nickel and its alloys

The laws governing the change in thermal emf of nickel and some of its alloys after they are doped are considered. It is concluded that important data on the structure of the d-band can be obtained by measuring the absolute thermal emf of transition metals and their alloys.     

Influence of low temperature on the surface deformation of deformable mirrors

The two factors which influence the low temperature performance of deformable mirrors(DMs) are the piezoelectric stroke of the actuators and the thermally induced surface deformation of the DM. A new theory was proposed to explain the thermally induced surface deformation of the DM: because the thermal strain between the actuators and the base leads to an additional moment according to the theory of plates, the base will be bent and the bowing base will result in an obvious surface deformation of the facesheet. The finite element method(FEM) was used to prove the theory. The results showed that the thermally induced surface deformation is mainly caused by the base deformation which is induced by the coefficient of thermal expansion(CTE) mismatching; when the facesheet has similar CTE with the actuators, the surface deformation of the DM would be smoother. Then an optimized DM design was adopted to reduce the surface deformation of the DMs at low temperature. The low temperature tests of two 61-element discrete PZT actuator sample deformable mirrors and the corresponding optimized DMs were conducted to verify the simulated results. The results showed that the optimized DMs perform well.     

Effect of the twisting chirality configuration on the electromechanical behavior of multilayer superconducting tapes

Seeking a geometry that can withstand greater transverse loads based on the electromechanical material properties of high-temperature superconducting (HTS) tape is an effective way of improving the transport performance of HTS cables. The cabling method requires the determination of the optimum twist angle of the HTS tape for withstanding transverse loads. This paper investigates the critical current characteristics of HTS tapes under combined deformation. The limit range of the twist angle under the combined deformation is measured and the optimum twist angle of the HTS tape is determined. The results show that the twisting chirality configuration obviously affects the bending strength of the HTS tape. In the elastic range, increasing the pre-twist angle increases the bending strength of the HTS tape, thereby improving the transport performance. In addition, a numerical model is built to further investigate the effect of the twisting chirality configuration on the electromechanical properties of the HTS tape, and the experimental results are explained. The experimental and simulation results generally agree well, and calculations show that there is always a sharp change in stress at the interface of different materials. These findings explain the mechanism of the effect of the twisting chirality configuration on the mechanical behavior and critical current of the HTS tape. They also provide a reference for cabling methodologies for the HTS cable configuration.     

Kinetic effects in an La0.8Ba0.2MnO3 single crystal

Results are presented of a complex study of the magnetic and resistive properties, the Hall effect, the thermal emf, and the longitudinal Nernst-Ettingshausen effect of an La_0.8Ba_0.2MnO₃ single crystal at temperatures between 77 and 400 K. A maximum was observed near the Curie temperature T _c on the temperature dependences of the resistivity, the thermal emf, and the normal Hall coefficient. It was established that the Hall mobility remains constant near T _c. It is shown that these anomalies in the kinetic properties are attributable to a change in the position of the mobility edge relative to the Fermi level. A semiphenomenological theory is put forward to quantitatively describe the temperature and magnetic-field dependences of the resistivity and thermal emf of lanthanum manganites near the phase-transition temperature.     

Anomalous thermal electromotive force in samarium monosulfide

The thermal emf in samarium monosulfide was investigated at temperatures between 300 and 530 K. At T=435–455 K, an anomalous increase in the emf was found. This effect is explained by a noncoherent change in the valency of samarium ions.     

Thermomechanical properties of amorphous hydrogenated carbon–germanium alloys

Thermomechanical properties of amorphous hydrogenated carbon-germanium alloys prepared by the rf sputtering technique were determined for films in the 0 at. % to 100 at. % carbon content range. The stress, thermal expansion coefficient, and elastic modulus were obtained using the thermally induced bending technique. The stress was related to the concentration of hydrogen and argon, to the difference in the Ge-Ge and Ge-C bond length, and to the carbon hybridization. The thermal expansion coefficients of pure amorphous germanium and amorphous carbon are higher than that of their corresponding crystalline counterparts, which was attributed to the compressive stress of the films. The biaxial modulus, on the other hand, are always smaller than that of their crystalline counterparts, but increases as the concentration of carbon increases due to the substitution of Ge-Ge bonds by energetically stronger Ge-C and C-C bonds. Received: 9 May 2000 / Accepted: 10 May 2000 / Published online: 13 July 2000     

Calculation of the temperature dependence of the thermal emf in amorphous alloys CaxAl1−x and AuxNi1−x

The temperature dependence of the thermal emf of Ca_xAl_1–x and Au_xNi_1–x for four different concentrations of the components of the alloys is calculated on the basis of the concept of dynamic concentrated excitations in amorphous metal systems. It is shown that increasing x from 0.15 to 0.50 in Au_xNi_1–x raises the thermal emf, and a further increase in the Au concentration from 0.50 to 0.80 lowers S(T). For Ca_xAl_1–x the dependence S(T) is calculated in the interval of Ca concentrations from 0.55 to 0.75. In this concentration interval the thermal emf decreases as x is increased. It is shown that for both types of alloys the S(T) curve bends abruptly at a temperature near 10T₀ (where T₀ is the concentration-dependent characteristic temperature of amorphous alloys separating the ranges of strong and weak scattering of electrons by dynamic concentration excitations). The so-called S(T) knee shifts toward lower temperatures when the thermal emf increases with increasing x and toward higher temperatures when S(T) decreases with increasing x. The results agree with experimental data.Institute of Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 43–48, August, 1994.     

纳秒级脉冲激光诱导Zn掺杂过程中GaN/Al2O3材料的温度分布及热形变解析分析

分析了纳秒级脉冲激光作用下GaN的激光诱导Zn的掺杂过程.利用简化的一维模型，给出一种比较直观的脉冲激光辐照下GaN/Al₂O₃材料温度分布的解析形式，得到了GaN材料表面温度与激光辐照时间的关系以及材料形变与深度的关系.在激光脉冲作用时，GaN材料表面的温度与辐照时间的平方根成正比.脉冲过后，材料温度分布梯度和热形变分布随深度发生变化，接近表面的温度梯度最大，热形变量也最大.而在连续脉冲作用时表面的温度呈锯齿状不断升高. 关键词： 激光诱导 2O₃')" href="#">GaN/Al₂O₃ 温度分布 热形变     

Plastic deformation modeling of backward extrusion process for Nd–Fe–B ring magnets

3D finite element-based software (3D DEFORM) was used to simulate the thermal extrusion process of nanocrystalline magnetic ring. The effective stresses and effective strains for a ring magnet at different stages of the extrusion process were determined by simulation. The effective strains at different stages are displayed. The effective stresses on the cross section are determined by simulation. The test results of magnetic properties were of good validation of the three-dimensional finite element analysis for nanocrystalline backward extruded ring. 3D finite element-based plastic deformation simulation is proved to be an effective way to analyze the hot extrusion process of nanocrystalline magnetic ring, and to provide guiding for the mold design of thermal extrusion.     

Molecular Dynamic Simulation of High Speed Deformation Effect on Microstructure Change in Thermal Heated Metals

In the present paper computer simulation of high-speed deformation (shock wave propagation) by molecular dynamic method is performed in thin copper sample, having the form of rectangular parallelepiped (10 a ‐ 10 a ‐ 20 a , where a is the lattice constant) with 8000 atoms. On the surfaces Z 0 =0 and Z max =20 a the mirror boundary conditions with rigid walls and the periodic boundary conditions along X and Y directions corresponding to short sides of deformed crystal are used, which allows to investigate the reflection of shock wave from the surfaces in Z direction. The changes of microstructure have been investigated up to 12 ps. The numerical calculations of microstructure changes have been performed here taking into account the effect of thermal heating of crystal lattice before shock wave front. The numerical results show that comparing with the propagation of shock waves under room temperature in thermal heated structure additional displaced atoms (vacancies and interstitials) are produced. The obtained results show that the production of point defects during high-speed deformation is determined by the thermal softening of microstructure and generation rate of point defects very strong increases with an increasing of high speed deformation rate. The peculiarities of microstructure changes in deformed copper are analyzed here at the different initial temperatures and various high-speed deformations (average ion velocities behind shock wave).     

Elasticity and anelasticity of microcrystalline aluminum samples having various deformation and thermal histories

The effect of the amplitude of vibrational deformation on the elastic modulus and internal friction of microcrystalline aluminum samples produced by equal-channel angular pressing was studied. The samples have various deformation and thermal histories. The elastic and inelastic (microplastic) properties of the samples are investigated. As the degree of plastic deformation increases, the Young’s modulus E, the amplitude-independent decrement δ_i, and the microplastic flow stress σ increase. As the annealing temperature increases, the quantities δ_i and σ decrease noticeably and the modulus E exhibits a more complex behavior. The experimental data are discussed under the assumption that the dislocation mobility depends on both the spectrum of point defects and the internal stresses, whose level is determined by the degree of plastic deformation and the temperature of subsequent annealing. The concept of internal stresses is also used to analyze the data on the effect of the degree of deformation and annealing on the rupture strength of the samples.     

Peculiar behavior of structure rearrangement in nanofiber of intermetallic Ni<Subscript>3</Subscript>Al,containing long-period paired thermal anti-phase boundaries,under high-rate tensile uniaxial loading along <001>

Using molecular dynamics simulations, peculiarities of structure rearrangement in nanofiber of intermetallic Ni₃Al containing long-period, paired, thermal (nonconservative) anti-phase boundarties (APBs is investigated in the course of high-rate, tensile uniaxial loading along <001>. Four main deformation stages are determined (quasi-elastic, plastic, material flow and rupture), with each stage revealing particular features of structure transformations and energy transfer. The presence of periodic thermal planar defects in the long-period nanostructure (combined thermal anti-phase boundaries) significantly affects the onset of plastic deformation. A change in the type of thermal APBs in the long-period structure in turn affects the time to total rupture of nanofiber under plastic deformation condition. For the thermal AA 1/2 < 110 > {001}APBs, the time to total nanofiber rupture is slightly decreased, while that for the thermal AB 1/2 < 110 > {001} APBs is considerably increased.     

Thermal reaction characterization of micron-sized aluminum powders in CO<Subscript>2</Subscript>

The thermal reaction characterization of micron-sized aluminium powder in carbon dioxide were investigated by simultaneous thermal analysis technology (TG/DSC), using a series of heating rates (5, 10, 15, 20°C/min). The results showed that the reaction process of micron-sized aluminium powder in carbon dioxide was divided into three stages: the initial slow oxidation stage, the sharp oxidation stage and the last oxidation stage. The thermal performance was increased with the increase in the heating rates. Evolution of the samples was determined by collecting the products at the initial, sharp, and last oxidation stages of the process. The reaction products morphology was examined using scanning electron microscopy (SEM). The corresponding chemical changes were analysed by X-ray diffraction spectrometry (XRD). The effects of heating rate on the thermal reaction characteristics were discussed. A new reaction mechanism of micron-sized Al particle in CO₂ with gradually increased temperature was proposed.     

Electrical transport measurements in TiS3

Results of measurements of conductivity and Hall coefficient in the temperature range 15–300K and of thermal emf in the temperature range 80–400K, carried out on TiS₃ samples, are reported. The results indicate that these crystals are semiconducting with extrinsic n-type conductivity. The mobility of the carriers is about 30 cm²/V sec at room temperature, increases up to about 100 cm²/V sec at 100K and drops at lower temperatures. The Seebeck coefficient is in qualitative agreement with these findings but its detailed temperature dependence is not yet understood.