Superconductors are known to have zero electric resistance under conditions of extremely low temperatures. Electron flow, responsible for formation of electric current, moves in these conducting materials without colliding with atoms of their crystal lattices, thus without any heating losses. Nowadays superconductors are used for building high-capacity magnets for expensive research equipment and for high-precision diagnostic medical devices.

A material starts showing superconducting properties, when external magnetic field intensity, temperature or strength of flowing electric current reach some certain values. Russian researchers from the Institute of Physics of Metals and Research Institute of Inorganic Materials have studied how material synthesis methods influenced values of critical current.

Researchers have made superconducting fibers of tin niobate (Nb_{3Sn) by means of so-called bronze technology, which provided insertion of niobium fibers into a bronze matrix with high content of tin. High temperature makes tin atoms react with fibers, thus forming nanocrystalline grains of superconducting tin niobate. Appropriate combination of conditions, like temperature and heating time, as well as tin concentration, result in no unreacted niobium atoms left at fiber cross sections after annealing. During fiber synthesis researchers often add a small amount of titanium for helping atoms of niobium and tin to find correct position in space in order to form superconducting grain of given extra small size – about 60 – 80 nanometers.}

 

 

Titanium can also be added to a bronze matrix or become a part of niobium fibers before annealing process starts. Russian physicists have compared physical properties of superconducting materials, which were synthesized by means of two different techniques. Results were very interesting – it appeared that value of critical current density, at which superconductivity was eliminated, was significantly different in these materials. When titanium was added to bronze matrix, critical current density of a superconductor was 980 amperes per square millimeter. When another technique was applied, and titanium was added to niobium fibers, critical current density of a superconductor was 780 amperes per square millimeter.

Microphotographs of superconducting structures told researches that without alloying by titanium, a superconducting material still contained islets of pure unreacted niobium, which was a not so good conductor. In this case, tin niobate grains were heterogeneous by size, which had another negative effect on superconductivity. Titanium promoted formation of homogeneous tin niobate grains no matter how it was added, but when a part of bronze matrix, not fibers, it had more pronounced positive effect.

Authors of the research admitted that all experimental samples of tin niobate had contained islets of pure niobium, which didn’t react with tin. These results mean that critical current values still have to be improved.