Supercondutors show zero electrical resistance at low temperatures. The flow of electrons creating the electric current moves there without colliding with the atoms of the crystal lattice of the conducting material; that means that there is no heat loss. Today, superconductors are used to create high-power magnets for expensive scientific equipment and highly accurate medical diagnostic devices.
A material manifests its superconducting properties at certain levels of the external field intensity, temperature or current power. Researchers at the Institute for Physics of Metals, Ural Branch of Russian Academy of Sciences; and the Research Institute for Inorganic Materials, have studied the dependence of the level of the critical current on the method of material production.
Irina Deryagina and her colleagues were generating superconducting tin niobate (Nb3Sn) fibers using the bronze technology where niobium fibres are enclosed into a bronze matrix with an elevated tin level. Heating makes the tin atoms react with the fibres forming nanocrystal grains of superconducting Nb3Sn. Provided the right conditions (the temperature and heating time, and tin concentration), the transverse sections of the fibres have practically no niobium atoms that have not reacted after annealing. Small amounts of titanium are often added during the fibre production process which facilitates the correct positioning of the niobium and tin atoms to create superconducting grains of small fixed sizes (about 60–80 nanometer).
Titanium can be added in the bronze matrix or it can be implemented in the niobium fibres structure before annealing. The researchers compared the physical properties of the superconducting materials produced using two different methods and discovered that the level of critical current density causing superconductivity to disappear differs significantly as well. If titanium is added to the bronze matrix the critical current density for the resultant conductor is 980 А/mm2. When titanium atoms are added to niobium fibres, the level reduces to 780 А/mm2. The research supported by the Presidium of Russian Academy of Sciences was published in the Siberian Federal University Journal.
The physicists studied the microphotographs of the resultant structures. Without titanium alloying, pure niobium areas are preserved in the material, that did not react with the tin and showed lower current conducting ability. The Nb3Sn grains in such samples are heterogeneous in size which has a negative effect on the superconductor. Titanium facilitates the formation of homogeneous Nb3Sn grains with the use of any chosen method of alloying; but if they are put in the matrix together with tin and not in the niobium fibres, however, the positive effect is more pronounced.
The researchers note that even the best samples generated in the course of the experiments contain areas of pure niobium that has not reacted with tin. It means that the achieved levels of critical current are below the maximum and there is room for improvement. “The results of the work show us the direction for improving the technology to create multi-fibre conductors,” say the researchers.
Source of information:
L. Deryagina, Е. N. Popova, Е. G. Zakharevskaya, Е. P. Romanov, А. Е. Vorobyeva, Е. А. Dergunova, С. M. Malaev. “The Effect of the Alloying Method and the Composite Geometry on the Structure of Nb3Sn Nanocrystal Layers in Nb/Cu-Sn Superconducting Composites.” The Siberian Federal University Journal. Series: Mathematics and Physics. 2011, vol. 4, #2.
Mikhail Petrov published by STRF.ru