Superconductors and superconducting materials conduct electricity without resistance. They are metals, ceramics, organic materials, and heavily-doped semicondcutors that lose resistance to the flow of electrical current below a temperature called the critical temperature (Tc) that is measured in degrees Kelvin (K).
Superconductors and superconducting materials are also able to maintain an electrical current without an applied voltage, making them suitable for use as electromagnets. When placed in a weak, external magnetic field, superconductive materials are penetrated for only a short distance in a phenomenon called the Meissner effect. Applications for superconductors and superconducting materials include electromagnets as found in magnetic resonance imaging (MRI) machines.
Types of Superconductors and Superconducting Materials
There are two basic types of superconductors and superconducting materials: Type 1 and Type 2. Type 1 superconductors consist of a single metal or metalloid. They are slightly conductive at room temperature, but become superconductive when cooled to their critical temperature. Although copper, silver and gold are excellent electrical conductors at room temperature, the strong coupling between their electrons and lattice structure explains their lack of superconductivity. Other elements, such as lithium, can become Type 1 superconductors with the application of high levels of pressure. Unlike 1 Type 1 superconductors, Type 2 superconductors and superconducting materials are often made of metallic compounds and alloys. They have higher critical temperatures. In addition to the Type 1 and Type 2 classification system, superconductors and superconducting materials can be categorized by their dimensional structure.
Although most superconducting materials are three-dimensional, some organic superconductors and surface-doped superconductive materials are two-dimensional. Single-walled carbon nanotubes can exhibit one-dimensional superconductivity, but are more widely known for their near-infinite thermal conductivity. Superconductors and superconducting materials with high optical reflectivity and reduced surface friction are also available. Suppliers of superconductors and superconducting materials characterize products in terms of their constituent materials . For example, Type 2 superconductors are sometimes called alloy superconductors, metallic superconductors, or all-metal superconductors. Superconducting alloys and compounds include niobium nitride, vanadium silicon, and alloys made of niobium and titanium that are used in superconducting wire. Ceramic superconductors and superconducting materials are inorganic compounds formed by the reaction of a metal with carbon, nitrogen, oxygen, or silicon. Ceramic superconductor systems are also comprised of bismuth, strontium, calcium, copper and oxygen with a small amount of lead.