VR. SoBolo.N. Mazurenkoand A.A. Drozd(Institute of Solid State and Semiconductor Physics
,
ASB P. Brovka Str.
,
17
,
Minsk 220072
,
Belarus)
金属学报(英文版)
Galvanomagnetic properties of metals at boiling point of liquid helium and some prob-lems relating to Joule heating in cylinder conductors are investigated by the method of voltage current characteristics. Radial current under an external coaxial magnetic field is used to get high magnetoresistance of conductor. High level of magnetore-sistance in this geometry offers the possibility to investigate a wide range of heat generation. The stabilization of voltage observed in definite current range is discussed in terms of analysis of heat aspects of problem when a heat genemtion function and heat elimination they are regarded at helium temperuture. An electric temperature ordering of system is proposed as a factor responsible for voltage stabilization when the presence of more heated and less heated sections along conductor radius is connected with negativity of derivative of heat elimination function with respect to temperature between first and second boiling crisis.
关键词:
galvanomagnetic property
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null
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Journal of Applied Physics
Amorphous BC2N powders were prepared by mechanical milling with hexagonal boron nitride and graphite as starting materials. A bulk amorphous BC2N compound was produced by sintering the as-milled amorphous BC2N powders in a vacuum of 10(-5) Torr at a temperature of 1470 K. The conductivity measurement for the bulk amorphous BC2N compound showed that it behaves as a semiconductor with band gap energy of 0.11 eV for temperatures ranging from room temperature to 560 K and a semimetal for temperatures between 560 and 740 K. The mechanism of the formation of the amorphous BC2N powders is discussed. (C) 1998 American Institute of Physics.
关键词:
bc2n
Physica Status Solidi B-Basic Research
The spin Hamiltonian parameters, g factors and the hyperfine structure constants for Co4+ (3d(5)) and Ir4+ (5d(5)) in SrTiO3 are theoretically studied from the formulas of these parameters for an nd(5) (n = 3 and 5) ion in a tetragonally distorted octahedron with low spin S = 1/2. According to the theoretical analyses, the impurity-ligand bond lengths R-parallel to' parallel to the C-4 axis are found to be larger than the host values R-parallel to based on the phase transition rotation angles phi of the [TiO6](8-) octahedron by the C-4 axis at 4.2 and 77 K, respectively. The elongation of the ligand octahedra in the host may be enhanced in the impurity centers by the Jahn-Teller effect of the nd(5) ions. The theoretical results based on the above local structures show good agreement with the experimental data.
关键词:
electron-paramagnetic-resonance;atomic screening constants;phase-transition;optical-absorption;scf functions;doped srtio3;degrees k;crystals;ions;spectra
Journal of Materials Science
Solid state amorphizations in mechanically deformed Ni/Ti multilayer composites have been investigated by differential scanning calorimetry and X-ray diffraction. The growth of amorphous alloy in our Ni/Ti composites was facilitated by the large number of grain boundaries and relatively large degree of disorder induced in the metal layers by the cold rolling. The formation of different products of solid-state reaction in the Ni/Ti composites has bee,n elucidated in terms of magnetic and enthalpy analysis. It is thought that the solid state amorphization occurs first during heating, followed by the formation of intermetallic compounds through direct solid-state reaction of elemental nickel and titanium and by the crystallization of the amorphous alloy already formed by the solid state amorphization reaction. The values of the activation energy for interdiffusion and interdiffusion coefficient for the formation of amorphous alloy in the Ni/Ti composites have also been calculated.
关键词:
diffusion couples;interdiffusion reactions;elemental composites;thin-films;ni/zr;ni;planar;binary;growth;alloys
Chemical Physics Letters
The magnetism and the electronic structures of Ti-doped AlN are studied by the first-principles calculations. It is found that Ti prefers to substitute Al site in AlN host, and this doped configuration favors the ferromagnetic ground state. The magnetic moment of the supercell containing single Ti(Al) is 1.00 mu B. Electronic structures suggest magnetic moments mainly come from the doped Ti atom, Ti-doped AlN is n-type ferromagnetic semiconductor and the ferromagnetism can be explained by double-exchange mechanism. For O and Ti co-doped AlN, calculations show O(N) defect would induce magnetic moments increasing and change Ti-doped AlN from semiconductor to metal. Crown Copyright (C) 2009 Published by Elsevier B. V. All rights reserved.
关键词:
room-temperature;gan
Journal of Physical Chemistry C
Polymer nanocomposites are usually made by incorporating dried narroparticles into polymer matrices. This would easily lead to aggregation of nanoparticles and then would readily bring about opaqueness for narrocomposites based on functionally transparent polymers. In this work, preparation of highly transparent ZnO quantum dots (ZnO-QDs)/epoxy nanocomposites that can emit intense luminescence was reported for the first time by uniformly dispersing ZnO quantum dots in a transparent epoxy resin via a direct dispersion method. The direct dispersion of ZnO quantum dots without drying in the epoxy matrix could effectively avoid aggregation of fine quantum dots and showed a good dispersity of ZnO-QDs in the epoxy matrix. Such materials showed a high transparency in the visible region and exited a broad emission spectrum peaked at 442 nm. On the other hand, in traditional solid state lighting emission diodes, semiconductor quantum dots are used as phosphors that are attached to the die of the lighting emission diode (LED) lamps for emitting luminescence. In this work, the as-prepared ZnO-QDs/epoxy nanocomposites were successfully employed as packaging materials for solid state lighting emission diodes in which conventional phosphors are not required while the nanocomposite encapsulating materials are responsible for emitting luminescence and thus the encapsulated LED lamps have an innovative structure. Consequently, the as-prepared ZnO-QDs/epoxy nanocomposites are promising for use as novel encapsulating materials in LED technology due to the much simplified encapsulating process.
关键词:
polymer nanocomposites;size quantization;zinc acetate;nanoparticles;luminescence;colloids;photochemistry;oxide;particles;diodes
Physical Review B
Metastable Fe100-xAlx alloys have been formed by ball milling of elemental Fe and Al powders: supersaturated body-centered-cubic solid solutions for x less than or equal to 70, and an amorphous phase for x > 70. Quantitative x-ray-diffraction measurements show that the total root-mean-square displacement (rms) and the static rms in the Fe100-xAlx solid solutions increase significantly with increasing Al content, The total rms at the instability point, however, reaches only 6.8% of the nearest-neighbor distance and is far below the critical value predicted by the Lindemann melting criterion, suggesting that the Lindemann melting criterion is not applicable for the solid-state amorphization. Instead. the Debye temperature of the supersaturated Fe100-xAlx alloys was observed to drop by similar to 22% at the point of amorphization, implying a corresponding softening in the average shear modulus of similar to 40%, which agrees with the microhardness measurements. These results strongly support the empirical elastic instability criterion For the solid-state amorphization process.
关键词:
to-glass transition;crystal;transformation
Journal of Alloys and Compounds
Growth kinetics and interfacial morphologies of the intermetallic compounds (IMCs) between single crystal Ag and Sn-4Ag, Sn-3Cu and Sn-37Pb solders were investigated by solid-state aging at 160 degrees C and liquid-state aging at 260 degrees C. Isothermal equation of chemical reaction and phase diagrams were used to explain the effects of Ag, Cu and Pb on the growth kinetics of IMCs under solid-state and liquid-state aging conditions. The diffusion coefficients for the three solder joints of Sn-4Ag/Ag, Sn-3Cu/Ag and Sn-37Pb/Ag were calculated after solid-state and liquid-state aging. It is found that Pb can effectively retard the growth of IMCs during liquid-state aging but has little influence on the growth rate of IMCs during the solid-state aging. Some local small cracks were frequently observed in the Cu(6)Sn(5) particles near interfaces of the Sn-3Cu/Ag solder joints after solid-state aging for several days. However, there were no such local small cracks when solders or interfaces did not contain the Cu(6)Sn(5) particles after the same aging time. (C) 2008 Elsevier B.V. All rights reserved.
关键词:
Ag single crystal substrate;Lead-free solder;Intermetallic compounds;(IMCs);Growth kinetics;Local cracks;lead-free solders;electroless ni(p) metallization;intermetallic;compound;cu-sn;joints;ni;bi;nanoindentation;microstructure;wt.percent
