[attachment=2196]


HIGH TEMPERATURE SUPERCONDUCTORS
Historical Background
¢ Kamerlingh Onnes, Dutch physicist in 1911
¢ Meissner and Ochsenfeld
¢ Niobium nitride-16k, in 1941
¢ Vanadium-silicon-17.5k in 1953
¢ First commercial superconducting wire-NbTI,in 1962
¢ BCS Theory in 1957 by Bardeen, Cooper and Schrieffer
¢ Josephson Effect in1962
¢ Organic superconductors in 1964
¢ HTS in 1986 by Muller & Bednorz
¢ Yr,Ba,Cu,O compound- 90k in 1987
¢ Latest ceramic superconductor,Tc=138k, compound of Hg,Ta,Ba,Ca,Cu,O
Unconventional Superconductors
¢ Mainly artificially made superconductors
¢ Cant be explained by BCS theory
¢ HTS like La based cuprate perovskite, Mg diboride etc.
Meissner Effect
¢ By Walther Meissner & Robert Ochsenfeld
¢ At superconducting temperature materials become perfectly dia magnetic & cancels all flux entering inside or the process of excluding the magnetic field
¢ Working principle of high speed magnetic trains
Perovskite
¢ A rare mineral on the earth crust
¢ HTS material
¢ Named after the Russian mineralogist L.A.Perovski
¢ Also named for the general group of crystals having the same structure
¢ Modern HTS are perovskites

High Temperature superconductors
¢ Contains Cu oxide planes as a common structural feature
¢ Works with the help of liquid N as coolant
¢ Doesn™t follow BCS theory
¢ Made by mixing oxides & heating in furnaces with adequate oxygen supply
Making of Yr,Ba,Cu,Oxide HTS
¢ Mixing the chemicals
¢ Calcination
¢ Intermediate firings
¢ Final oxygen annealing
Even better superconductors
¢ Repeating the regrinding & oxygen annealing
¢ Using high temperatures for heating
¢ Oxygen annealing for long firing periods
¢ Grinding the material to a very fine powder before final annealing
¢ By protecting from moisture
A typical and Future Superconductors
¢ Fullerene superconductors
¢ Organic superconductors
¢ Heavy fermions
¢ Fluroargentates superconductors
¢ Ceramic superconductors
¢ Praseodymium 123 superconductors