SUPERCONDUCTOR is an element, inter-metallic alloy, or a compound that will conduct electricity without resistance. This property is called superconductivity.

Once set in motion, electrical current will flow forever in a closed loop of superconducting material.

Superconductivity is also sometimes referred as "macroscopic quantum phenomenon."

The second property of these materials is perfect diamagnetism i.e. that the superconducting material will exclude a magnetic field which is known as the Meissner effect.

Superconducting materials can be categorized into one of two types:
  1. Type I Superconductors - which totally exclude all applied magnetic fields. Most elemental superconductors are Type I. Very pure samples of lead, mercury, and tin are examples of Type I superconductors.
  2. Type II Superconductors - which totally exclude low applied magnetic fields, but only partially exclude high applied magnetic fields; their diamagnetism is not perfect but mixed in the presence of high fields. Niobium is an example of an elemental Type II superconductor. YBa2Cu3O7 (YBCO) and Bi2CaSr2Cu2O9 are examples of. High temperature Type II ceramic superconductors.

Both types exhibit perfect electrical conductivity, and can be restored to 'normal' conductors in the presence of a sufficiently strong magnetic field.