Superconductivity, Its Types and Applications PDF

Superconductivity Superconductivity is defined as the complete disappearance of electrical resistance in various solids when they are cooled below a characteristic temperature. This temperature, called the transition temperature, varies for different materials but generally is below 20 K (...

Superconductivity Superconductivity is defined as the complete disappearance of electrical resistance in various solids when they are cooled below a characteristic temperature. This temperature, called the transition temperature, varies for different materials but generally is below 20 K (−253 °C). Such type of solid is called Superconductor. Discovery-Superconductivity was discovered in 1911 by the Dutch physicist Heike Kamerlingh Onnes; he was awarded the Nobel Prize for Physics in 1913 for his low-temperature research. Kamerlingh Onnes found that the electrical resistivity of a mercury wire disappears suddenly when it is cooled below a temperature of about 4 K (−269 °C); absolute zero is 0 K, the temperature at which all matter loses its disorder. He soon discovered that a superconducting material can be returned to the normal (i.e., nonsuperconducting) state either by passing a sufficiently large current through it or by applying a sufficiently strong magnetic field to it. 1  TYPES OF SUPERCONDUCTORS Type I or soft superconductors Type II or Hard Superconductors 2  Type I or soft superconductors These are usually made of pure metal. When it is cooled below its critical temperature it exhibits zero resistivity and displays perfect diamagnetism. This means that the magnetic fields cannot penetrate it while it is in the superconducting state. They strictly obey Meissner Effect. These are called soft superconductors because they give away their nature at very low field strength. They do not have any useful technical applications. Example: Pure specimens of Al,Pb,Hg,Indium etc. 3  Type II or Hard Superconductors These superconductors are usually alloys or transition metals with high values of electrical resistivity. Their diamagnetism is more complex. They have two critical magnetic fields Hc1 and Hc2. These allow the magnetic field to penetrate it. Thus they do not obey Meissner effect. These are called Hard superconductors because relatively large fields are required to bring them back to normal state. These are used for strong field superconducting metals and hence are technically more useful than soft superconductors. These can carry large currents. Example: transition metals and alloys consisting of niobium, Al,Si and vanadium etc. 4 Diagrams 5 APPLICATIONS OF SUPERCONDUCTORS Used in cables :For electric power transmission without any loss. For Producing very strong magnetic fields of about 20-30 tesla which are used in power generators and in medical diagnostic equipments. To fabricate high field magnets used in NMR spectrometers. Magnetic energy can be stored in large superconductors to counter voltage fluctuations. They are used to perform logic and storage functions in computers. These are used to produce electromagnetic shields. 6 APPLICATIONS OF SUPERCONDUCTORS Used in the fabrication of small IC chips of electronic devices and computers. Used as magnetic separators in ore refining. Superconducting film can be used as phonon detector or nuclear radiation detector. In magnetic levitation trains. 7 8