Super Conductors

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super conductors pesentation is about the introduction of super conductors and its properties,types and applications..

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Super Conductors

  1. 1. Super Conducting Materials <ul><li>Introduction. </li></ul><ul><li>Super conductivity. </li></ul><ul><li>Properties of Super conductors. </li></ul><ul><li>BCS Theory (Qualitative). </li></ul><ul><li>Types of Super conductors. </li></ul><ul><li>High T C Super conductors. </li></ul><ul><li>Applications of Super conductors. </li></ul>
  2. 2. Introduction: <ul><li>Superconductors , materials that have no resistance to the flow of electricity, are one of the last great frontiers of scientific discovery. </li></ul><ul><li>In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes of Leiden University When he cooled it to the temperature of liquid helium, 4 degrees Kelvin (-452F, -269C), its resistance suddenly disappeared. </li></ul><ul><li>In 1913, he won a Nobel Prize in physics for his research in this area. </li></ul><ul><li>Super conducting materials have extra ordinary. </li></ul><ul><li>electrical and magnetic characteristics. </li></ul><ul><li>Super Conducting materials have many important. </li></ul><ul><li>applications in the field of engineering & technology. </li></ul>
  3. 3. Super conductivity: <ul><li>Definition: The phenomenon of sudden disappearance of electrical resistance in a material, when it is cooled below a certain temperature is known as Super conductivity. </li></ul><ul><li>The temperature at which a material at normal conducting state changes into super conducting state is known as transition temperature or critical temperature ( T C ) . </li></ul><ul><li> T C of a super conducting element is in the range of 0K to 9.5K. </li></ul>10.0 Niobium Titanium (NbTi) 4. 17.5 Niobium Tin (   Nb 3 Al ) 3. 4.15 Mercury(Hg) 2. 3.40 Indium(In) 1. T C (K) Element S.No
  4. 4. Properties of Super conductors: <ul><li>Zero electrical resistance: </li></ul><ul><li>- The electrical resistance of the superconductors of the superconductor is zero below the transition temperature ( T C ). </li></ul><ul><li>- This property of Zero electrical resistance is known as </li></ul><ul><li>‘ defining property’ of a super conductor. </li></ul><ul><li>Effect of Magnetic Field: </li></ul><ul><li>- Below T C superconductivity can be destroyed by the application of a strong magnetic field. </li></ul><ul><li>- Minimum magnetic field strength required to destroy the super conducting property at any temperature is known as Critical magnetic field (H C ), </li></ul><ul><li>H 0 Critical M.field at 0K. </li></ul><ul><li> T C Super conducting transition </li></ul><ul><li>temperature. </li></ul><ul><li>T is the temperature below T C </li></ul>
  5. 5. Electrical resistance in Super conductors :
  6. 6. Properties of Super conductors: <ul><li>Effect of electric current: </li></ul><ul><li>- The application of very high electrical current to a superconducting material destroys its super conducting property. </li></ul><ul><li>- Consider a wire made up of super conductor (i) be the current in wire. </li></ul><ul><li>- Flow of high current induces a magnetic field,this induce magnetic field in the conductor destroys the super conducting property. </li></ul><ul><li>- The critical current i C required to destroy the super conducting property is given by, </li></ul><ul><li>i C = 2  r H C </li></ul><ul><li>Where, </li></ul><ul><li>H C is the critical magnetic field. </li></ul><ul><li>r is the radius of the super conducting wire. </li></ul>
  7. 7. Properties of Super conductors: <ul><li>Persistent current: </li></ul><ul><li>-Super conducting ring – magnetic field – current in ring- electro magnetic induction. </li></ul><ul><li>-In normal conducting state – current decreases due to resistance in wire – since in super conducting state it has zero resistance once current set up it flows. </li></ul><ul><li>- A steady current which flows through a super conducting ring withut any decrease in its strength as long as the material is in super conducting state is called Persistent current . </li></ul><ul><li>- Persistent current persists even after the removal of the magnetic field. </li></ul>
  8. 8. Properties of Super conductors: <ul><li>Meissner Effect: </li></ul>
  9. 9. Properties of Super conductors: <ul><li>Isotope Effect: </li></ul><ul><li>- In most of the cases, the isotope of a super conducting element is also a super conductor. </li></ul><ul><li>- T C of a heavier isotope is lower than that of a lighter isotope. </li></ul><ul><li>- Maxwell found that T C are inversely proportional to tha atomic masses of the isotopes of a single super conductor. </li></ul>
  10. 10. Properties of Super conductors: <ul><li>Effect of Pressure: </li></ul><ul><li>- By applying high pressure, we can bring the T C of a material nearer to room temperature, i.e., T C is directly proportional to pressure. </li></ul><ul><li>Thermal properties: </li></ul><ul><li>- Entropy and specific heat decreases at transition temperature. </li></ul><ul><ul><ul><li>- Thermo-electric effect disappears in the super conducting state. </li></ul></ul></ul><ul><li>Stress: </li></ul><ul><li>- When a stress applied to a super conducting material its dimensions varies. </li></ul><ul><li>Frequency: </li></ul><ul><li>- At very high frequencies, the zero resistance of a superconductor is modified.The T C is not affected by the frequency vibration. </li></ul>
  11. 11. Properties of Super conductors: <ul><li>Impurity: </li></ul><ul><li>The general properties especially the magnetic property of super conducting state are modified by the addition of impurities. </li></ul><ul><li>Size: </li></ul><ul><li>If the size of the specimen is reduced below 10 -4 cm , the properties of super conducting state are modified. </li></ul><ul><li>Josephson Effect: </li></ul><ul><li>- In the year 1962, Brian Josephson, an English Physicist discovered the tunneling of super conducting electron pair with opposite spin and momenta through a thin (10-20 Å ) insulating barrier between two super conductors. This phenomenon is known as Josephson Effect. </li></ul>
  12. 12. Properties of Super conductors: <ul><li>- An arrangement of two super conductors or a normal metal and a super conductor separated by a thin insulator (normally an oxide) barrier is called Josephson junction. </li></ul><ul><li>- DC Josephson Effect: The tunneling of super conducting electron pairs through Josephson junction leads to the flow of current without a voltage drop. This phenomenon is known as DC Josephson Effect. </li></ul><ul><li>- AC Josephson Effect: When a DC voltage is applied across the Josephson junction through which super current is flowing, an AC current (high frequency current oscillations) is noticed. This phenomenon is known as AC Josephson effect. </li></ul>
  13. 13. BCS Theory (Qualitative): <ul><li>- The microscopic theory of super conductivity developed by J.Bardeen, L.N.Cooper and J.R.Schriffer in 1957, successfully explained the effects like zero resistivity, this theory is known as BCS Theory. </li></ul><ul><li>Important features of BCS theory: </li></ul><ul><li>- Electrons form pairs called Cooper pairs which propagate throughout the lattice. </li></ul><ul><li>- The propagation of copper pairs is without resistance because the electrons move in resonance with phonons,therefore the interaction described by the BCS theory is known as electron-phonon interaction. </li></ul>
  14. 14. Types of Super conductors. <ul><li>Based on the magnetization behavior of super conductors in an external magnetic field, they are classified into two types, </li></ul><ul><li>(i) Type – I super conductors. </li></ul><ul><li>(ii) Type – II super conductors. </li></ul><ul><li>(i)Type – I super conductors: In this super conductor, the magnetic field is totally expelled from the interior of the material below a certain magnetising field H C . At H C, the material loses its superconductivity abruptly and the magnetic field penetrates fully( Soft super conductors ). </li></ul><ul><li>(ii)Type – I super conductors: In which the material losses its magnetisation gradually rather than suddenly ( Hard super conductors ). </li></ul><ul><li>Based on the super conducting transition temperatures, the super conductors are classified into two types, </li></ul><ul><li>(i) Low – temperature super conductor. </li></ul><ul><li>If T C is low, less than 20K such super conductors are called as Low – Temperature super conductors. They are also known as elemental super conductors. It is not in practical use due to ultra-low transition temperature. </li></ul><ul><li>(ii) High – temperature super conductor. </li></ul>
  15. 15. Types of Super conductors. Ex; Nb-Sn, Nb-zr, Nb-Ti etc., Ex: lead, tin, Hg etc., 6. They are called Hard super conductors. They are called soft super conductors. 5. Mixed state is present. No mixed state exists. 4. There are two critical magnetic field ( H C ) ie lower critical field ( H C1 ) and upper critical field ( H C2 ) There is only one critical magnetic field ( H C ) 3. They do not exhibit complete Meissner effect They exhibit complete Meissner effect I.e they are completely diamagnetic 2. The material loses its magnetisation gradually. The material loses its magnetisation suddenly. 1. Type – II super conductors. Type – I super conductors. S.No
  16. 16. Types of Super conductors. Ex; Nb-Sn, Nb-zr, Nb-Ti etc., Ex: lead, tin, Hg etc., 6. They are called Hard super conductors. They are called soft super conductors. 5. Mixed state is present. No mixed state exists. 4. There are two critical magnetic field ( H C ) ie lower critical field ( H C1 ) and upper critical field ( H C2 ) There is only one critical magnetic field ( H C ) 3. They do not exhibit complete Meissner effect They exhibit complete Meissner effect I.e they are completely diamagnetic 2. The material loses its magnetisation gradually. The material loses its magnetization suddenly. 1. Type – II super conductors. Type – I super conductors. S.No
  17. 17. High T C Super conductors. <ul><li>In a super conductor if the transition temperature is high ie.,greater than 20K, then it is called as high-temperature super conductors. </li></ul><ul><li>In 1986, Muller and Bednorz discovered high tempertaure super conductor in Ceramics. </li></ul><ul><li>Some of the high T C super conductors and their T C values, </li></ul>S.No High T C Super conductors T C in K 1. La 1.85 Ba 0.15 CuO 4 36 2. YBa 2 Cu 3 O 6.9 90 3. Tl 2 Ba 2­ Ca 2 Cu 3 O 10 125 4. HgBa 2 CaCu 2 O 6 133
  18. 18. High T C Super conductors.
  19. 19. High T C Super conductors. <ul><li>Crystal structure of YBa 2 Cu 3 O 9-x </li></ul><ul><li>- crystal structure is of the product obtained is related to the cubic perovskite structure. </li></ul><ul><li>- Three BCC are placed one above the another.Te distribution of atoms in the unit cells is as shown, </li></ul><ul><li>Cu atom at the body corners : 8x1/8x3=3. </li></ul><ul><li>Ba atom at two body centres : 1x2 = 2. </li></ul><ul><li>Yt atom at one body centre : 1x1=1. </li></ul><ul><li>O at mid-points of edges : 12x1/4x3=9. </li></ul>
  20. 20. Applications of Super conductors: <ul><li>SQUID : </li></ul><ul><li>-SQUID stands for Super conducting QUantum Interference Device. </li></ul><ul><li>-It is an ultra-sensitive instrument used to measure very weak magnetic field of the order of 10 -14 tesla </li></ul><ul><li>Application: </li></ul><ul><li>- SQUID can be used to detect the </li></ul><ul><li>variation of very minute signals </li></ul><ul><li>in terms of quantum flux. </li></ul><ul><li>- It can also be used as storage </li></ul><ul><li>device for magnetic flux. </li></ul><ul><li>-SQUID is useful in the study of earth </li></ul><ul><li>quakes, removing paramagnetic impurities, </li></ul><ul><li>detection of magnetic signals from the </li></ul><ul><li>brain and heart. </li></ul>
  21. 21. Applications of Super conductors: <ul><li>Cryotron: </li></ul><ul><li>- Cryotron is a magnetically operated current switch. </li></ul><ul><li>Magnetic levitation: </li></ul><ul><li>- When a super conducting material shows the Meissner effect. Due to this effect, super conducting materials strongly repel external magnets. This leads to a levitation effect. </li></ul><ul><li>- When a magnet is placed over a super conductor, it floats. This phenomenon is known as Magnetic Levitation. </li></ul><ul><li>- Magnetic levitated Train(Maglev train) </li></ul><ul><li>Additional applications: </li></ul><ul><li>- Super conducting Magnets. </li></ul><ul><li>- Electrical Machines. </li></ul><ul><li>- Power cables. </li></ul><ul><li>- Computer memory devices. </li></ul>
  22. 22. Applications of Super conductors:
  23. 23. Super conductors:
  24. 24. Thank you…… Presented By, C.Madan Kumar, Lecturer in Physics,ciet.

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