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superconductivity

superconductivity

royabhi
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superconductivity

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  1. SUPERCONDUCTIVITY SUBMITTED BY:ABHISHEK ROY UDAI PRATAP AUTONOMOUS COLLEGE

  2. CONTENT • Superconductors • Discovery • Properties • Important factors • Types • Meissner Effect • High Tc Superconductors • BCS Theory

  3. Introduction • What are superconductors? • Superconductors are the material having almost zero resistivity and behave as diamagnetic below the superconducting transiting temperature. • Superconductivity is the flow of electric current without resistance in certain metals,alloys, and in some cases at temperature hundreds of degrees above absolute zero.

  4. Discoverer of superconductivity • Superconductivity was first discovered in 1911 by the Dutch physicist, Heike KammerlinghOnnes.

  5. DISCOVERY • During the course of experiment Onnes found that- • Resistivity of mercury vanished abruptly at 4.2 k Normal State Tc=Transition temperature T>Tc Normal State T<Tc Superconducting State Superconducting State

  6. Main Aim Of Superconductivty P=I2R IF R=0 Then P=0 i.e No power loss

  7. GENERAL PROPERTIES • Electrical Resistance- Virtualy zero electrical resistance • Effect of impurities- When impurities are added to superconducting elements,thesuperconductivity is not loss but the Tc is lowered • Effect of pressure and stress- Certain materials exhibits superconductivity on increasing the Pressure in superconductors ,the increase in stress results in increase of the Tc value.

  8. SUPERCONDUCTING STATE • The superconducting state is defined by three very important factors 1. Critical temperature (Tc) 2. Critical field (Hc) 3. Critical current density (Jc). • Each of these parameters is very dependant on the other two properties present.

  9. Critcal Temperature-The temperature at which a material electrical resistivity drops to absolute zero is called Critical temperature or transition temperature.

  10. CRITICAL TEMPERATURE

  11. Critical Field(Hc)- An external applied magnetic field above which superconductors becomes non-conducting.This minimum magnetic fields required to destroy the superconducting state is called the critical magnetic field Hc. Hc=Ho [1-(T/Tc)2 ] H0=Critical Field at 0k Hc=Critical value of applied Magnetic Field ForT=TcHc=0 For T= 0 K Hc=Ho

  12. Critical Current Density • Similarly,there is a critical current above which zero resistivity is lost, which limits the environment in which certain superconductors can be used.

  13. Isotope Effect- The critical or transition temperature Tc value of a superconductors is found to vary with its isotopic mass i.ethe transition temperature is inversly proportional to the square root of isotopic mass of single superconductors.” Tc α 1/√M Magnetic Field Effect- If Strong magnetic field is applied to a superconductors below its Tc, the superconductors undergoes a transition from superconducting state to normal state.

  14. MEISSNER EFFECT • The complete expulsion of all magnetic field by a superconducting material is called Meissner Effect. • The Meissner effect is a distinct characteristics of a superconducting from a normal perfect conductor.This effect is exhibited by the superconducting materials only when the applied field is less then the critical field Hc. MEISSNER

  15. TYPE-1(SOFT SUPERCONDUCTORS) TYPE-2(HARD SUPERCONDUCTORS) TYPES OF SUPERCONDUCTORS

  16. TYPE-1 TYPE-2 • Soft superconductors are those which can tolerate impurites without affecting the superconducting properties. • Only one critical field exist for these superconductors. • Exhibit Meissnereffect. • E.g: Pb,Hg,Zn etc • Hard superconductors are those which cannot tolerate impurities,i.e. , the impurity affects the superconducting property. • Two critical fields Hc1(lower)& Hc2 (upper) for these. • Don’t exhibit Meissner effect. • E.g:Nb3Ge,Nb3Si

  17. Superconductors having their Tc values above the temperature of liquid Nitrogen (77K or-196 C) are called the high temperature superconductors. • High temperature superconductors have high Tc values. • They are not metal or intermetallic compounds but oxides of copper in combination with other elements. • They are brittle and easy to form wires and tapes. • HTSC WIRES/ TAPES provide transmission of electrical power over a long distance without any resistive loss. HIGH Tc SUPERCONDUCTORS(HTSC)

  18. BCS THEORY -When a metal is cooled to the critical temperature, electrons in the metal form Cooper Pairs. -Cooper Pairs are electrons which exchange phonons and become bound together. -Bound electrons behave like bosons. Their wavefunctions don’t obey Pauli exclusion rule and thus they can all occupy the same quantum state. -The BCS theory of Superconductivity states that bound photons have slightly lower energy, which prevents lattice collisions and thus eliminates resistance. -.

  19. THANK YOU

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