Niobium-Tin Superconductor

Niobium-tin is a Type II superconductor with a critical temperature of 18K and a critical magnetic field of 24.5 Tesla. These properties give it potential for constructing superconducting magnets, and it has been used for that purpose. It can withstand the highest current densities (up to 200,000 Amperes per square centimeter) at the highest working magnetic field (15 T). It has the mechanical disadvantage of being very brittle so that it cannot be drawn into wires for making magnet coils. To make magnet coils, separate strands of niobium wrapped in tin are made and then heated to fuse these materials into the niobium-tin alloy. Because of these mechanical difficulties, the makers of superconducting magnets have turned to niobium-titanium for the construction of magnet coils.

Lanthanum-Barium-Copper-Oxide

As the first of a new class of high-temperature superconductors, this superconductor has generated an enormous amount of research (18,000 publications in 4 years). The understanding which has emerged is that copper-oxide layers provide the path for current. These copper-oxide layers are separated by layers of other atoms which serve as spacers and charge reservoirs.

Power Applications of YBCO

Leading in attempts to provide superconducting power lines made from high-temperature superconductors are the yttrium compound referred to as YBCO and the bismuth compounds BSCCO.

For operation at liquid nitrogen temperature, YBCO has some advantages in retaining high current densities under strong magnetic fields. It has been most successfully used in the form of epitaxial thin films or as single crystals. Most of the current research focuses on ways to form useful thin films of the material on various metal substrates. Current densities over a million amps/cm^2 have been achieved at 77K.

Bismuth Strontium Copper Oxides

Commonly referred to in current literature as BSCCO, this ceramic has shown critical temperatures as high as 110 K. A leading candidate for power applications of high-temperature superconductors, it is used in two main forms:

A great deal of effort is currently being put into forming superconducting tapes of these materials by a method called "powder in tube" forming. Tapes over a kilometer long have been made from the Bi-2223 material which will sustain a current density above 10,000 A/cm^2 at 77 K. The Bi-2212 material must be kept below 20K, but is superior at those temperatures.

"Powder in Tube" Forming

Thallium-Barium-Copper Oxide