Ya. D. Starodubov

Critical current, pinning, and the resistive state of superconducting single-crystal niobium with various types of defect structure

The critical current, pinning, and resistive state of single-crystal niobium of texture orientation are studied in various structural states obtained by rolling by 42% at 20 K and subsequent polishing of the surface layers. It is found that the heterogeneous structures typical of the strained sample have a lower current-carrying capacity even after thinning to ∼10% on account of the enhancement of the thermomagnetic instability in the parts with fragmented structure in the subsurface layers. For the case of a homogeneous defect structure of the mid-region of a sample with a uniformly distributed dislocation density of 1.3×1011 cm−2 in the resistive state a correlation between the component of the normal current and the critical current density is found, in accordance with the concepts of flux creep due to the scatter of the local values of Jc.

Change of the superconducting, transport, and microscopic properties of transition metals upon introduction of interstitial impurities and deformation-induced defects

For group-V transition metals (Nb, Ta) containing different concentrations of interstitial impurities (O, C, N, H) and deformation-induced defects, a numerical calculation of various effective microscopic characteristics averaged over the Fermi surface and of the band parameters in the framework of the Friedel model is carried out using the experimentally determined values of the superconducting transition temperature Tc and the temperature dependence of the resistivity in the interval Tc<T≲300 K. The causes of the polar character discerned in the influence of interstitial impurities and dislocations on the investigated physical characteristics are discussed.

Superconducting properties and structure of vanadium after cryogenic deformation

The effect of low temperature (77 K) deformation by drawing (80%) on the superconducting properties and structure of vanadium is studied. The structural elements (fragment boundaries) responsible for the observed changes of critical parameters are isolated. The electron-phonon coupling constant and the electron mean free path undergo most significant changes in these regions of rotational deformation localization, which have a high density of defects and are powerful sources of internal stresses. The dislocation density at the fragment boundaries is estimated.

Resistivity and microscopic characteristics of platinum in different structural states

The experimental temperature dependence of the resistivity of platinum in different structural states is processed using the two-band Mott–Wilson model of a transition metal. It is found that impurities, deformation defects, and quenching defects have essentially different influences on the Debye temperature, the intensity of electron–electron Coulomb scattering, and the intensity of intra- and interband electron–phonon scattering. A number of effective microscopic characteristics and band parameters are calculated in the Friedel model. The mechanisms by which the different structural factors influence the investigated complex of physical characteristics of platinum are analyzed.

Structure parameters and degradation of the critical current of the alloy NT-50 after cryogenic drawing in an ultrasonic field

The parameters of the defect and phase structure of the alloy NT-50 are investigated after low-temperature (77 K) deformation by drawing in an ultrasonic field, and the influence of these parameters on the amount of degradation of the critical current under tensile loading at 4.2 K is studied. It is found that cryogenic ultrasonic deformation leads to intensified decomposition of the β-solid solution with precipitation of Ti-rich phases according to the kinetics of the spontaneous martensitic transformation and results in a reduction of the internal stress level in the alloys. The structural features found promote stabilization of the β-solid solution during a subsequent deep cooling, as is manifested in a lowering of the degree of completion of the low-temperature deformation-induced martensitic transformation, which in turn raises the threshold for degradation of the critical current and reduces the degree of degradation in a wide range of external mechanical loads.

About the nature of inelastic deformation of HTSC ceramics in region temperature below Tc

Abstract For Y- and Bi-based ceramics in superconducting state the results of the experimental studying the deformation under the loading are presented. The acoustic emission signals, the peculiarities of the intrinsic friction spectrum and ones of the planar contact resistance are studied. These results confirm the full analogy of the inelastic deformation processes at T c for HTSC ceramics and for metals.

Investigation of flux-trapping effect in Bi-based ceramics at 65–300 K

The influence of low magnetic fields on the temperature dependence of attenuation decrement is studied. The conservation of this effect after field switching off is discovered.

On the softening effect in superconducting state

It is shown that in superconducting state the increase of creep rate and peculiariries of attenuation decrement have dislocation origin.

The effect of low-temperature strain on the structure and the critical-current degradation of the superconducting alloy Nb-Ti

The structural-phase aspects of the behavior of the critical current under load in the superconductive alloy Nb–48.5 wt% Ti are studied. It is shown that the optimum preliminary strain at T=77 K with subsequent annealing suppresses the tendency of the β matrix of the alloy to undergo phase transformations according to martensitic kinetics under uniaxial tension at T=4.2 K, and this is manifested in the reduction of the critical-current degradation effect when loaded to σ=0.9σfr in a transverse magnetic field of H=5 T. The paper discusses possible critical-current degradation mechanisms under mechanical loading in the niobium-titanium alloy, based on models of critical current flow in the β matrix reinforced with martensitic interlayers.

Low-temperature anomalies of the physico-mechanical characteristics of pseudoamorphous titanium nickelide

A study is made of the structure, mechanical properties, and electrical resistance of crystalline and pseudoamorphous (obtained by rolling at 300 K by 50 and 90%) titanium nickelide in both the initial state and after annealing to different temperatures in the interval 513–893 K. It is found that the resistivity of polyamorphous Ti–Ni exceeds 200 μΩ⋅cm, falls off monotonically with increasing annealing temperature, and has a minimum in the low-temperature region 4.2–50 K (Tmin=17–19 K). In the temperature interval 4.2–20 K a nonmonotonic temperature dependence of the ultimate strength of polyamorphous Ti–Ni is observed which increases with increasing degree of deformation by rolling of the investigated material. The results are analyzed. It is conjectured that the observed anomaly of the temperature dependences of the ultimate strength and resistivity are due to low-temperature polyamorphism of the pseudoamorphous Ti-Ni in the temperature interval 10–20 K.