Superconductivity


Superconductivity is the ability of certain materials to conduct electrical current with no resistance and extremely low losses. This ability to carry large amounts of current can be applied to electric power devices such as motors and generators, and to electricity transmission in power lines. For example, superconductors can carry as much as 100 times the amount of electricity of ordinary copper or aluminum wires of the same size.


Scientists had been intrigued with the concept of superconductivity since its discovery in the early 1900s, but the extreme low temperatures the phenomenon required was a barrier to practical and low-cost applications. This all changed in 1986, when a new class of ceramic superconductors was discovered that "superconducted" at higher temperatures. The science of high-temperature superconductivity (HTS) was born, and along with it came the prospect for an elegant technology that promises to "supercharge" the way energy is generated, delivered, and used.

History of Superconductivity
Early in the 20th century, Dutch physicist Heike Kamerlingh Onnes observed that mercury displayed no electrical resistance when cooled to very low temperatures. With this observation, the study of superconductivity was born.


For the next several decades, superconductors remained a scientific curiosity with few practical applications. Then in the 1960s a practical superconducting metal wire made of niobium and tin was developed. That wire, later made of a niobium and titanium alloy, became the basis for the first applications of superconductors.


The niobium and titanium alloy, still in use today, is among the materials called low-temperature superconductors. Low-temperature superconductors must be cooled to below 20 Kelvin (K) (-253o Celsius [C]) in order to become superconducting. They are now widely used in magnetic resonance imaging, or MRI, machines, and in the fields of high-energy physics and nuclear fusion. Additional commercial use has been limited largely by the high refrigeration costs associated with liquid helium, which is needed to cool the materials to such low temperatures.


The hope for low-cost superconductivity was ignited by two significant discoveries in the 1980s. In 1986, two IBM scientists in Zurich, Alex Müller and Georg Bednorz, discovered a new class of superconductors. Unlike the low-temperature superconductors, which were metallic or semimetallic, these new compounds were ceramic and were superconducting up to 35 K (-238oC). Müller and Bednorz won a Nobel Prize for their discovery. Then in 1987, Paul Chu at the University of Houston took the discovery one step further and announced a compound that became superconducting at 94 K (-179oC). This discovery was particularly significant because this compound could be cooled with cheap and readily available liquid nitrogen. These new materials were dubbed high-temperature superconductors.


Today's high-temperature superconductors are moving out of the laboratory and into the marketplace. Bismuth-based compounds are being fashioned into superconducting wires and coils, which are essential to electric power uses. Thallium- and yttrium-based compounds are being formed into the thin films used in electronic devices. And, as superconductivity moves into the 21st century, products such as superconducting motors, generators, fault-current limiters, energy storage systems, and power cables promise to change forever the way electricity is generated, delivered, and used.

Superconductor Uses
Transmission lines that carry power without resistance, medical diagnostic tools that eliminate the need for surgery, "levitating" trains that speed along the tracks—these are not visions of the future, but examples of what superconductors are doing today.


Superconductors conduct electricity without losing energy to electrical resistance, as most conductors do. Certain materials become superconductors when they are cooled to very low temperatures. Low-temperature superconductors exhibit superconductivity at temperatures near 0 Kelvin (K) (or -273o Celsius [C]). Recently discovered high-temperature superconductors (HTS) can function at temperatures as high as 140 K (-133oC). This is an exciting discovery because these high-temperature superconductors can be cooled more economically and efficiently than can low-temperature superconductors.


Superconductors also repel surrounding magnetic fields. This phenomenon is demonstrated when we levitate a magnet above a cooled superconductor, and it is the force at work in Japan's famous Maglev train.


Superconductors help us use energy more efficiently and reduce the cost of electricity production, storage, transmission, and use, and the costs of transportation and medical equipment. Some current uses, and some that hold the most promise for the near future, are these: (The following documents mentioned below are available as Adobe Acrobat PDFs. Download Acrobat Reader.)