There are two types of superconductivity: type 1 and type 2. Type 1 is generally seen in pure elements
, while type 2 is usually seen in specially prepared superconducing alloys.
Type 1 superconductivity is much less resistant to magnetic fields and "high" temperatures. In a type 1 material, it is either fully superconducting or not superconducting at all (i.e. there is only one transistion point)
Type 2 superconductivity acts like type 1 until a certain transition point. Once past that first transition point, some atoms of the material is superconducting while others are not. The material still acts like a superconductor in this state. It is not until the second transition point that the material loses all its superconductivity. The second transition point is usually much higher than the transition point of type 1, so type 2 materials keep their superconductivity under much higher magnetic field intensities and temperatures.
Type 1 materials usually can only be superconducting at liquid helium temperatures and under very low magnetic fields of a small fraction of a tesla. However, some type 2 materials can keep up their superconducting properties at liquid nitrogen temperatures and under large fields of several teslas!