共查询到20条相似文献,搜索用时 0 毫秒
1.
A. A. Bykov K. Yu. Terent’ev D. M. Gokhfeld M. I. Petrov 《Physics of the Solid State》2012,54(10):1947-1950
The fractal dimension of the boundaries of clusters formed by pores and granules in polycrystalline materials is shown to be determined by the sample density and crystallite sizes. The dependence of the fractal dimension on the density has a maximum. It is shown that the maximum diamagnetic response can be obtained in a porous high-temperature superconductor with a porosity of 50?C60% and small crystallite sizes. 相似文献
2.
3.
N. K. Maksimova V. M. Kalygina V. P. Voronkov A. P. Vyatkin 《Russian Physics Journal》1993,36(10):935-943
To study the nature and properties of potential barriers in gallium arsenide devices, we have investigated structural phase transitions in GaAs contacts with multilayer films containing refractory transition-metal borides (TiB2, LaB6). We verified the important role in degrading Schottky barrier device performance played by local mechanical stresses introduced at the interface by lateral nonuniformities in interphase interactions. We examine the electrical properties of MIS gallium arsenide devices, taking into account the high density of electronic surface states (ESS). We show it is possible to control the density of ESS by selecting the dielectric, and we discuss its deposition and annealing with a pulsed laser. We discuss the nature of potential barriers in gallium arsenide devices, drawing upon our data and previously published data and modern theoretical models.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 10, pp. 52–62, October, 1993. 相似文献
4.
S. N. Ivanov E. N. Khazanov A. V. Taranov I. S. Mikhailova V. M. Gropyanov A. A. Abramovich 《Physics of the Solid State》2001,43(4):665-669
Elastic properties and thermal-phonon scattering are investigated in Al2O3+0.3% MgO ceramics and cermets of different porosities based on them. The cermets, reinforced with a metallic frame of the steel 12X18H9T, are obtained by dry compaction followed by sintering. It is shown that the elastic moduli of cermets are determined by their porosity and that the grain boundaries can be investigated in detail by a nonequilibrium-phonon propagation method. 相似文献
5.
L. A. Kulakova 《Physics of the Solid State》2001,43(8):1468-1475
Acoustic investigations of layered crystals KY(MoO4)2 and glassy alloys Si20Te80 (with inclusions of nanocrystallites) are performed with the purpose of elucidating the character of binding forces in layered materials. The absorption and velocity of sound, as well as the spatial evolution of the spectrum of acoustic fluxes in various directions in wide ranges of temperatures (90–300 K), frequencies (14–1800 MHz), and intensities (0.04–100 W/cm2) of sound, are measured. Acoustooptical and pulse-echo methods were used for the measurements. A theoretical analysis of the data obtained has revealed anomalously large values of the nonlinear elastic coefficients and anharmonicity constants of longitudinal phonon modes that are determined by the anharmonicity of binding forces across the layers and at boundaries with nanocrystallites. It is shown that the anisotropy of the mechanical strength of layered crystals is to a large extent determined by the anharmonicity of binding forces. 相似文献
6.
Oriano Bottauscio Valeria Chiadò Piat Michela Eleuteri Luca Lussardi Alessandra Manzin 《Physica B: Condensed Matter》2012,407(9):1417-1419
This paper is devoted to the determination of the equivalent anisotropy properties of polycrystalline magnetic materials, modelled by an assembly of monocrystalline grains with a stochastic spatial distribution of easy axes. The mathematical theory of is applied to homogenize the anisotropic term in the Gibbs free energy. The procedure is validated focusing on the micromagnetic computation of reversal processes in polycrystalline magnetic thin films. 相似文献
7.
Digital speckle micro-metrology system, which is a combination of a long-focus microscope and a digital image-measuring device, is developed for studying the micro-mechanics behavior of the interphase of bimaterials. The natural texture of a specimen's surface is thought as a carrier of deformation's information and is analyzed to obtain the displacement field in each step, strain field and their real-time variation of the interphase. The resolution of the micro-metrology system is 10 nm for in-plane displacements. In this paper, the micro-metrology system is employed to investigate the micro-mechanics behavior of the interphase under thermal impulsing. The experimental results show that the interphase is the main factor affecting the mechanical characteristic of the whole composite structure. 相似文献
8.
9.
B.D. Dunlap 《Journal of magnetism and magnetic materials》1983,37(2):211-214
The paramagnetic susceptibility of polycrystalline materials having large magnetic anisotropies is considered. It is shown that polycrystalline data in many case may not reflect strong crystalline electric field phenomena, even though these are clearly seen in single crystal data. 相似文献
10.
A. I. Korobov N. I. Odina A. N. Ékonomov A. N. Badulina T. V. Ageeva 《JETP Letters》2006,84(3):127-129
Temperature dependences of the photoacoustic signal magnitude and the relative velocity variation of longitudinal ultrasound in polycrystalline titanium are measured. Anomalous behavior of these quantities is observed in the temperature region corresponding to the electronic topological transition in a titanium single crystal. The results of measurements are interpreted as an experimental verification of the possibility for the anomalies associated with the electronic topological transition to “survive” in a polycrystalline metal. 相似文献
11.
《Composite Interfaces》2013,20(2-3):297-317
In this paper an attempt was made to define microstructural properties of carbon fiber/PP composites, with respect to fiber surface chemistry and morphology. In order to define the effects of the fiber surface sizings and morphology on the polymer microstructure, the interphase and mechanical properties of the composites, carbon fibers with similar, but not identical surface chemistry (CH and CT) were used. Characterization was performed by several techniques: SEM, POM, reflection microscopy, DSC, FTIR, XPS, contact angle measurements. For microstructural analysis, the geometrical method, method of intercept and DIF method were used. It was found that both carbon fibers have a strong influence on the nucleation mechanism and crystallization as well as on the microstructural parameters in the model and macro composites. Nucleation efficiency of the fibers has been confirmed by the nucleation parameter Q, measured by Muchova–Lednicky method and by the interfacial energy parameters. Microstructural analysis based on the photographs obtained by POM, SEM and reflection microscopy has shown that in the CH/PP model and macrocomposites the sieve-grain network was formed, which indicates better mechanical properties. The results obtained for the macromechanical properties of PP composites reinforced with CH and CT have confirmed the prediction based on micostructural analysis. 相似文献
12.
13.
Interdiffusion processes in epitaxial single-crystal Pd/Ag thin films within the temperature range 20°–500°C are studied by transmission electron microscopy, electron diffraction and electrical resistance methods. Homogenization is investigated both during deposition and during annealing.The mass transfer kinetics is found to depend significantly on the original structure of the interphase boundary (dislocations present or not) and on its reconstruction due to interdiffusion. Regular networks of misfit dislocations at the interface can retard interdiffusion, while network failures lead to acceleration of homogenization process. The vacancy flows play a decisive role in these processes. The effects of interphase dislocations on the DIGM, DIR and RID processes are discussed.The numerical study of electrical resistance variations during annealing is carried out. The concentration profiles are plotted for a nontrivial dependence of interdiffusion coefficient on concentration. The numerical results are compared with the experimental data. 相似文献
14.
Size effects on tensile and fatigue behaviour of polycrystalline metal foils at the micrometer scale
Tensile and fatigue properties of as-rolled and annealed polycrystalline Cu foils with different thicknesses at the micrometer scale were investigated. Uniaxial tensile testing results showed that with decreasing foil thickness the uniform elongation decreases for both as-rolled and annealed foils, whereas the yield strength and ultimate tensile strength increase for as-rolled foils, but decrease for the annealed foils. For both the as-rolled or annealed foils, bending fatigue resistance decreases with decreasing the foil thickness. Deformation and fatigue damage behaviour of the free-standing foils were characterised as a function of foil thickness. In addition, the fatigue strength of various small-scale Cu foils was compared to understand the physical mechanisms of size effects on mechanical properties of the metallic material at micrometer scales. 相似文献
15.
Characterizing the mechanical properties of soft materials and biological tissues is of great significance for understanding their deformation behaviors. In this paper, a regional stretching method is proposed to measure the elastic and hyperelastic properties of a soft material with an adhesive surface or with the aid of glue. Theoretical and dimensional analyses are performed to investigate the regional stretch problem for soft materials that obey the neo-Hookean model, the Mooney-Rivlin model, or the Arruda-Boyce model. Finite element simulations are made to determine the expressions of the dimensionless functions that correlate the stretch response with the constitutive parameters. Thereby, an inverse approach is established to determine the elastic and hyperelastic properties of the tested materials. The regional stretch method is also compared to the indentation technique. Finally, experiments are performed to demonstrate the effectiveness of the proposed method. 相似文献
16.
A. I. Slutsker A. B. Sinani V. I. Betekhtin A. A. Kozhushko A. G. Kadomtsev S. S. Ordanyan 《Physics of the Solid State》2008,50(8):1450-1457
A series of silicon carbide ceramic samples with variable characteristics of the microporosity and strength, such as the ballistic strength σ B and the static strength σ S , are investigated. The dependences of the strength on the integral porosity for ceramic materials are determined. It is established that the strength (both σ B and σ S ) is directly proportional to the average length of the bridges between micropores. The mechanism of the influence of microporosity on the strength of the ceramic materials is elucidated. According to this mechanism, interpore bridges are concentrators of stresses and, hence, are broken when a load is applied to the ceramic material. Numerous breakings of bridges bring about the failure of the ceramic body. The average stress concentration coefficient is estimated as a function of the integral porosity of the ceramic material. It is demonstrated that the static strength of the ceramic material is determined by the presence of large micropores (50–100 μm). 相似文献
17.
Optical and magnetic studies on CuO nanoparticles prepared by a chemical route are reported and the effect of size variation
on these properties is discussed. SEM images show that the nanoparticles are interlinked into microspheres with the cages
containing visible nanoscale holes. Diffuse reflectance spectroscopy indicates a consistent red shift in the fundamental band
gap (indirect band gap) from 1.23 to 1 eV as the size decreases from 29 to 11 nm. This observed red shift is attributed to
the presence of defect states within the band gap. A clear blue shift is observed in the direct band gap of these nanoparticles
presumably due to the quantum confinement effects. Air-annealed samples show a paramagnetic response whereas particles annealed
in a reducing atmosphere show additionally a weak ferromagnetic component at room temperature. For both types of particles,
the paramagnetic and ferromagnetic moments, respectively, increase with decreasing size. The role of oxygen vacancies is understood
to relate to the generation of free carriers mediating ferromagnetism between Cu spins. AC susceptibility measurements show
both the antiferromagnetic transitions of CuO including the one at 231 K which is associated with the onset of the spiral
antiferromagnetic phase transition. 相似文献
18.
M. G. Zemlyanov G. Kh. Panova G. F. Syrykh A. A. Shikov 《Physics of the Solid State》2006,48(1):139-143
Composites of Cu and Pb (immiscible in solid state) were prepared by melt spinning onto a copper disc. X-ray diffraction measurements
showed the Cu-Pb composites thus obtained to consist of Pb nanoparticles of a certain size embedded in a copper matrix. The
average size of the nanocrystalline Pb blocks was determined along the normals to the (111) and (200) reflecting planes, and
their size distribution was measured. The vibrational, electronic, and superconducting properties of the Cu85Pb15 and Cu50Pb50 composites were derived from low-temperature heat-capacity, magnetic-susceptibility, and resistance measurements, and the
contribution of Pb nanoparticles to the heat capacity was separated. The low-frequency excitation density in Pb nanocrystals
was found to increase as compared to that in crystalline Pb. The observed decrease of T
c correlates with the variation of Pb nanoparticles in size, which is a consequence of the size effect in the properties of
Pb nanocrystals. 相似文献
19.
20.
A semiquantitative technique for estimating the limits of the critical current density in polycrystalline high-temperature superconductors is presented. This technique is based on the transport properties of single grain boundaries. Various factors essential in deducing the critical current density of polycrystalline high-T
c materials from the characteristics of single grain boundaries are discussed. The results for tectured, polycrystalline YBa2Cu3O7 fibers are reported, and the influence of the microstructure on their critical current density is discussed. 相似文献