Materials physics and mechanics

RAR RUS 1-9 Naval Research Laboratory Pande C.S.

USA

Microstructural Aspects of High and Low Tc Superconductors The U.S. Navy has been developing superconducting homopolar motors for ship propulsion since 1969, initially using conventional NbTi superconducting material for the magnets. With the advent of high critical temperature (high Tc ) superconductors, NbTi has been replaced by bismuth-strontium-calcium-copper-oxide (BSCCO). Performance of these motors depends critically on the properties of the superconducting material specifically of the magnitude of the current density and its stability with time. Flux creep is a major concern in these materials, since it limits high Tc superconductor performance at temperatures above about 30K. As is well known these properties are strongly influenced by the high Tc superconductor microstructure. The level of current transport in a given high Tc superconductor depends upon several intrinsic microstructure-property relationships. In the typical orthorhombic crystal structure, superconducting current flows primarily in the a-b planes. In polycrystalline materials, superconducting current drops off as grain boundary misorientation increases. High current densities in polycrystalline materials needs strong c-axis alignment where current is expected to flow through those grains connected by low angle boundaries. When a magnetic field is applied, the flux vortices may shift due to the force from the current or to thermal activation, resulting in a loss of superconducting properties known as flux creep. Flux vortices may be pinned by microstructural defects such as grain boundaries or dislocations, if present in sufficient quantities, hence the importance of microstructure. The present paper deals with the microstructural aspects of superconductivity, specifically the role played by microstructure in determining superconducting properties. Examples from both the low and high Tc materials will be cited and future trends discussed. High Tc Superconductors; Low Tc Superconductors https://mpm.spbstu.ru/article/2000.3.1/ 2000_2_1_p1.pdf

RAR RUS 10-14 Institute of Problems of Mechanical Engineering RAS Baskov D.Yu.

St.Petersburg, Russia

0000-0003-0727-6352 Institute of Problems of Mechanical Engineering RAS Gutkin M. Yu.

St.Petersburg, Russia

Institute of Problems of Mechanical Engineering RAS I.A. Ovid’ko И.А.

St.Petersburg, Russia

113263 6701854079 0000-0001-9909-2950 Institute of Problems of Mechanical Engineering RAS Sheinerman Alexander

St.Petersburg, Russia

Misfit Dislocation Walls in Films with Alternate Layers We suggest a new mechanism for misfit strain accommodation in misfitting multilayer films with alternate layers through the generation of misfit dislocation walls. The detailed analysis of the necessary conditions for their appearance shows that, similar to one-layer films, misfit dislocation walls form above some critical film thicknesses which can be increased by varying the relation between thicknesses of adjoining film layers. Misfit Dislocation; misfit strain https://mpm.spbstu.ru/article/2000.3.2/ 2000_2_1_p2.pdf

RAR RUS 15-24 Electrotechnical University Vendik O.G.

St.Petersburg, Russia

St.Petersburg Electrotechnical University Vendik I.B.

St.Petersburg, Russia

St.Petersburg Electrotechnical University Kholodniak D.V.

St.Petersburg, Russia

Applications of High-Temperature Superconductors in Microwave Integrated Circuits A brief review is given of recent publications showing that the applications of hightemperature superconductors (HTS) in microwave technologies have become an integral part of industrial business. The basic components of microwave devices are HTS epitaxial films on dielectric substrates. It is shown that the properties of interfaces between the substrates and HTS films are crucially important for obtaining high-quality HTS films. The change of the structure in the process of film growth is related to the initial stage of HTS nucleation at the interface between the substrate and the film. The film surface resistance at microwave frequencies depends on the HTS film structure. It is known that one can decrease the surface resistance, which will permit designing higher-quality microwave-microelectronics components to operate at cryogenic temperatures by improving the film structure. A discussion is given how to improve the HTS film microwave properties to make possible industrial production of high-performance HTS devices and subsystems. High-Temperature Superconductors; Microwave Integrated Circuits https://mpm.spbstu.ru/article/2000.3.3/ 2000_2_1_p3.pdf

RAR RUS 25-30 Institute Silicate Chemistry of Russian Academy of Science Solovyeva E.N.

St.Petersburg, Russia

Institute Silicate Chemistry of Russian Academy of Science Pivovarov M.M.

St.Petersburg, Russia

Institute Silicate Chemistry of Russian Academy of Science Konakov V.G.

St.Petersburg, Russia

Thermodynamic Properties of the Systems Y(Ln)Ba2Cu3Ox The enthalpies of formation of Ry R’1-yBa2Cu3Ox (R, R’=Y, Nd, Eu; y=0; 0,5) have been determined at 298K by solution calorimetry. These values were shown for YBa2Cu3Ox to depend on the oxygen stoichiometry of a sample. The results of thermodynamic investigations were found to be in good agreement with the data of the kinetic investigations of the Y(Ln) Ba2 Cu3 Ox formation reactions. This agreement is explained in the aspect of electronic structure of lanthanide atoms. Y(Ln)Ba2Cu3Ox; solution calorimetry https://mpm.spbstu.ru/article/2000.3.4/ 2000_2_1_p4.pdf

RAR RUS 31-36 Institute of Problems of Mechanical Engineering RAS I.A. Ovid’ko И.А.

St.Petersburg, Russia

113263 6701854079 0000-0001-9909-2950 Institute of Problems of Mechanical Engineering RAS Sheinerman Alexander

St.Petersburg, Russia

Nano-islands on Plastically Deformed Substrates with Disclinations Spatial arrangements of nano-islands deposited on plastically deformed substrates containing wedge disclinations (defects of rotational type) are theoretically examined. It is shown that the elastic interaction between the nano-islands and the disclinations is capable of causing preferable spatial positions of nano-islands. The parameters of the substrate/nano-island systems are theoretically revealed that control spatial positions of nano-islands on disclinated substrates. Nano-islands; Plastically Deformed Substrates; Disclinations https://mpm.spbstu.ru/article/2000.3.5/ 2000_2_1_p5.pdf

RAR RUS 37-41 Institute of Solid State Physics Straumal B.B.

Moscow, Russia

Chalmers University of Technology Friesel M.

Gothenburg, Sweden

Grain Boundary Phase Transitions and their Influence on Properties of Polycrystals Grain boundary (GB) phase transitions can change drastically the properties of polycrystals. The GB wetting phase transition can occur in the two-phase area of the bulk phase diagram where the liquid (L) and solid (S) phases are in equlibrium. The GB wetting tie line appears in the L+S area. Above the temperature of the GB wetting phase transition a GB can not exist in equlibrium with the liquid bulk phase. The liquid phase has to substitute the GB and to separate both grains. The experimental data on GB wetting phase transitions in the systems Al– Sn, Al–Ga, Al–Sn–Ga, Cu–In, Cu–Bi, Fe–Si–Zn, Mo–Ni, W–Ni, Zn–Sn and Zn–In are analysed. The GB wetting tie line can continue in the one-phase area of the bulk phase diagram as a GB solidus line. This line represents the GB premelting or prewetting phase transitions. The GB properties change drastically when the GB solidus line is crossed by a change in the temperature or concentration. The experimental data on GB segregation, energy, mobility and diffusivity in the systems Cu–Bi, Al–Ga, Al–Pb and Fe–Si–Zn obtained both in polycrystals and bicrystals are analysed. Grain Boundary; Phase Transitions https://mpm.spbstu.ru/article/2000.3.6/ 2000_2_1_p6.pdf

RAR RUS 42-50 Peter the Great St. Petersburg Polytechnic University Melker A.I.

St.Petersburg, Russia

Peter the Great St. Petersburg Polytechnic University Romanov S.N.

St.Petersburg, Russia

Peter the Great St. Petersburg Polytechnic University Kornilov D.A. Computer Simulation of Formation of Carbon Fullerenes In this contribution, we report on a study of the growth of fullerens and carbon nanotubes from small clusters. A key factor in molecular dynamics modeling is the choice of interatomic potential. Ab initio molecular dynamics requires extensive computer resources, so that is outside the scope of most complex systems. We have developed simpler molecular dynamics model of charges at bonds which takes into account the electronic and atomic degrees of freedom and which can be implemented using a personal computer. Our approach has the possibility of studying the excited states formed by electronic transitions. The fundamental difference is that previously one considered only an atomic subsystem whereas now we have investigated both subsystems, atomic and electronic, simultaneously. We have found that the cluster growth is accompanied by the resonance of the electronic and atomic degrees of freedom Carbon; Fullerenes; Computer Simulation https://mpm.spbstu.ru/article/2000.3.7/ 2000_2_1_p7.pdf

RAR RUS 51-62 Saint Petersburg State University Khantuleva

St.Petersburg, Russia

Microstructure Formation in the Framework of the Nonlocal Theory of Interfaces A new hydrodynamic theory based on non-equilibrium statistical mechanics is developed to describe the structure formation in dynamically deformed materials. Self-consistent non-local formulation of the boundary-value problem for a high-strain-rate process is reduced to a nonlinear operator set similar to some resonance problems. The branching of solutions to the problem determines both scales and types of the formed internal structure. A penetration problem for a long flat rigid plate into a viscous elastic medium is considered accounting for the dynamic structure formation following the high-rate straining in the framework of the nonlocal self-consistent approach. The obtained approximate analytical solution has shown to describe three regimes: initial, transient and quasi-stationary. It has been demonstrated that the mesoscopic structure formation had been initiated by relative accelerations in a medium localized near the plate surface moving at high velocity. The mesoscopic structures formed during the initial stage of penetration can affect the steady-state stage. It is very important that the proposed self-consistent theory allows taking into account the feed-back influence of the mesoscopic effects on macroscopic movement of the plate. Nonlocal Theory of Interfaces; Hydrodynamic theory https://mpm.spbstu.ru/article/2000.3.8/ 2000_2_1_p8.pdf

RAR RUS 63-69 Institut National Polytechnique de Grenoble Tousimi

France

Ufa State Aviation Technical University Valiev R.Z.

Ufa, Russia

Institut National Polytechnique de Grenoble Yavari

France

Copper-Matrix Cu-HfO2 Nanocomposite Compacts of Full Density Cu/HfO2 nanocomposite powders were prepared by reactive milling under partial oxygen pressure as previously used to prepare Cu/ZrO2 nanocomposites. Cu/HfO2 nanocomposite powders with the same volumetric ceramic content were also prepared by direct milling of pure Cu with preformed HfO2 powder. Interestingly, in the case of preparation by treactive milling, the resulting HfO2 nanoparticles are amorphous. Direct milling of Cu and HfO2 powder did not result in any amorphisation of the latter. Full density compacts of the nanocomposite powders were prepared by hot uniaxial pressing under vacuum and by torsion straining at room temperature under a load of 5 GPa. The microhardness of the resulting compacts are reported. Copper; Nanocomposite; Uniaxial pressing https://mpm.spbstu.ru/article/2000.3.9/ 2000_2_1_p9.pdf