<P> In the extreme type - II limit, the problem of type - II superconductor in magnetic field is exactly equivalent to that of vortex state in rotating superfluid helium, which was discussed earlier by Richard Feynman in 1955 . </P> <P> In the vortex state, a phenomenon known as flux pinning, where a superconductor is pinned in space above a magnet, becomes possible . This is not possible with type - I superconductors, since they cannot be penetrated by magnetic fields . Since the superconductor is pinned above the magnet away from any surfaces, there is the potential for a frictionless joint . The worth of flux pinning is seen through many implementations such as lifts, frictionless joints, and transportation . The thinner the superconducting layer, the stronger the pinning that occurs when exposed to magnetic fields . </P> <P> Type - II superconductors are usually made of metal alloys or complex oxide ceramics . All high temperature superconductors are type - II superconductors . While most elemental superconductors are type - I, niobium, vanadium, and technetium are elemental type - II superconductors . Boron - doped diamond and silicon are also type - II superconductors . Metal alloy superconductors also exhibit type - II behavior (e.g. niobium - titanium and niobium - tin). </P> <P> Other type - II examples are the cuprate - perovskite ceramic materials which have achieved the highest superconducting critical temperatures . These include La Ba CuO, BSCCO, and YBCO (Yttrium - Barium - Copper - Oxide), which is famous as the first material to achieve superconductivity above the boiling point of liquid nitrogen (77 K). Due to strong vortex pinning, the cuprates are close to ideally hard superconductors . </P>

What are type i and type ii superconductors