presentation1-090415045351-phpapp01_2.ppt

8/9/2019 presentation1-090415045351-phpapp01_2.ppt

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Super Conducting MaterialsSuper Conducting Materials

Introduction.Super conductivity.Properties of Super conductors.BCS Theory (Qualitative).

Types of Super conductors.High T C Super conductors.

pplications of Super conductors.


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Introduction: Introduction:

o Superconductors ! "aterials that have no resistance to the flo# ofelectricity! are one of the last great frontiers of scientific discovery.

o In $%$$ superconductivity #as first o&served in "ercury &y 'utch

physicist Hei e a"erlingh *nnes of +eiden ,niversity -hen hecooled it to the te"perature of li uid heliu"! / degrees elvin (0/123!024%C)! its resistance suddenly disappeared.

o In $%$5! he #on a 6o&el Pri7e in physics for his research in this area.o Super conducting "aterials have e8tra ordinary. electrical and "agnetic characteristics.o Super Conducting "aterials have "any i"portant.

applications in the field of engineering 9 technology.


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Super conductivity:Super conductivity:

o Definition: The pheno"enon of sudden disappearance of electricalresistance in a "aterial! #hen it is cooled &elo# a certain te"peratureis no#n as Super conductivity.

o The te"perature at #hich a "aterial at nor"al conducting statechanges into super conducting state is no#n as transition te"peratureor critical te"perature (T C).

TC of a super conducting ele"ent is in the range of : to %.1 .

S.6o ;le"ent T C( )

$. Indiu"(In) 5./:

2. Mercury(Hg) /.$1

5. 6io&iu" Tin ( 6& 5 l ) $


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Properties of Super conductors:Properties of Super conductors:o =ero electrical resistance>

0 The electrical resistance of the superconductors of the superconductor is7ero &elo# the transition te"perature (T C ).

0 This property of =ero electrical resistance is no#n as?defining property@ of a super conductor.

o ;ffect of Magnetic 3ield>0 Belo# T C superconductivity can &e destroyed &y the application of a strong

"agnetic field.0 Mini"u" "agnetic field strength re uired to destroy the super conducting

property at any te"perature is no#n as Critical "agnetic field (H C )!

H : Critical M.field at : . T C Super conducting transition

te"perature.T is the te"perature &elo# T C


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Electrical resistance in SuperElectrical resistance in Super

conductorsconductors ::


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Properties of Super conductors:Properties of Super conductors:o ;ffect of electric current>

0 The application of very high electrical current to a superconducting"aterial destroys its super conducting property.

0 Consider a #ire "ade up of super conductor (i) &e the current in#ire.

0 3lo# of high current induces a "agnetic field!this induce "agneticfield in the conductor destroys the super conducting property.

0 The critical current i C re uired to destroy the super conducting property is given &y!

iC A 2 r H C-here!

HC is the critical "agnetic field.

r is the radius of the super conducting #ire.


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Properties of Super conductors:Properties of Super conductors:o Persistent current>

0Super conducting ring "agnetic field currentin ring0 electro "agnetic induction.

0In nor"al conducting state current decreases due

to resistance in #ire since in super conductingstate it has 7ero resistance once current set up itflo#s.

0 steady current #hich flo#s through a super conducting ring #ithut any

decrease in its strength as long as the "aterial is in super conducting stateis called Persistent current .0 Persistent current persists even after the re"oval of the "agnetic field.


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Properties of Super conductors:Properties of Super conductors:o Meissner Effect:


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Properties of Super conductors:Properties of Super conductors:o Isotope ;ffect>

0 In "ost of the cases! the isotope of a super conductingele"ent is also a super conductor.

0 TC of a heavier isotope is lo#er than that of a lighter isotope.

0 Ma8#ell found that T C are inversely proportional to thaato"ic "asses of the isotopes of a single super conductor.

M T

Const C

=

M T C

$

Const M =


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Properties of Super conductors:Properties of Super conductors:o ;ffect of Pressure>

0 By applying high pressure! #e can &ring the T C of a"aterial nearer to roo" te"perature! i.e.! T C is directly proportional to

pressure.o Ther"al properties>

0 ;ntropy and specific heat decreases at transitionte"perature.0 Ther"o0electric effect disappears in the super conductingstate.

o Stress>

0 -hen a stress applied to a super conducting "aterial itsdi"ensions varies.o 3re uency>

0 t very high fre uencies! the 7ero resistance of asuperconductor is "odified.The T C is not affected &y the fre uency

vi&ration.


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Properties of Super conductors:Properties of Super conductors:o I"purity>

The general properties especially the "agnetic property of superconducting state are "odified &y the addition of i"purities.

o Si7e>If the si7e of the speci"en is reduced &elo# $: 0/c"! the properties of

super conducting state are "odified.o osephson ;ffect>

0 In the year $%42! Brian osephson! an ;nglishPhysicist discovered the tunneling of super conducting

electron pair #ith opposite spin and "o"enta througha thin($:02: ) insulating &arrier &et#een t#osuper conductors. This pheno"enon is

no#n as osephson ;ffect.


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Properties of Super conductors:Properties of Super conductors:0 n arrange"ent of t#o super conductors or a nor"al "etal and a

super conductor separated &y a thin insulator (nor"ally an o8ide) &arrier iscalled osephson Dunction.

0 'C osephson ;ffect> The tunneling of super conducting electron pairs through osephson Dunction leads to the flo# of current #ithout avoltage drop. This pheno"enon is no#n as 'C osephson ;ffect.

0 C osephson ;ffect> -hen a 'C voltage is applied across theosephson Dunction through #hich super current is flo#ing! an C current

(high fre uency current oscillations) is noticed. This pheno"enon isno#n as C osephson effect.


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BCS Theory (Qualitative):BCS Theory (Qualitative):

0 The "icroscopic theory of super conductivity developed &y .Bardeen!+.6.Cooper and .E.Schriffer in $%1

effects li e 7ero resistivity! this theory is no#n as BCS Theory.I"portant features of BCS theory>

0 ;lectrons for" pairs called Cooper pairs #hich propagate throughout thelattice.0 The propagation of copper pairs is #ithout resistance &ecause the electrons"ove in resonance #ith phonons!therefore the interaction descri&ed &y the

BCS theory is no#n as electron0phonon interaction.


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Types of Super conductors.Types of Super conductors.Based on the "agneti7ation &ehavior of super conductors in an e8ternal"agnetic field! they are classified into t#o types!(i) Type I super conductors.(ii) Type II super conductors.

(i)Type I super conductors> In this super conductor! the "agnetic field is totallye8pelled fro" the interior of the "aterial &elo# a certain "agnetising fieldHC. t H C! the "aterial loses its superconductivity a&ruptly and the"agnetic field penetrates fully(Soft super conductors).

(ii)Type I super conductors> In #hich the "aterial losses its "agnetisationgradually rather than suddenly (Hard super conductors).Based on the super conducting transition te"peratures! the super

conductors are classified into t#o types!(i) +o# te"perature super conductor.If T C is lo#! less than 2: such super conductors are called as +o# Te"perature super conductors. They are also no#n as ele"ental superconductors. It is not in practical use due to ultra0lo# transition te"perature.(ii) High te"perature super conductor.


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Types of Super conductors.Types of Super conductors.S.6o Type I super conductors. Type II super conductors.

$. The "aterial loses its"agnetisation suddenly.

The "aterial loses its "agnetisationgradually.

2. They e8hi&it co"pleteMeissner effect I.e they areco"pletely dia"agnetic

They do not e8hi&it co"plete Meissnereffect

5. There is only one critical"agnetic field (H C)

There are t#o critical "agnetic field (H C)ie lo#er critical field (H C$) and uppercritical field (H C2)

/. 6o "i8ed state e8ists. Mi8ed state is present.

1. They are called soft superconductors.

They are called Hard super conductors.

4. ;8> lead! tin! Hg etc.! ;8F 6&0Sn! 6&07r! 6&0Ti etc.!


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Types of Super conductors.Types of Super conductors.S.6o Type I super conductors. Type II super conductors.

$. The "aterial loses its"agneti7ation suddenly.

The "aterial loses its "agnetisationgradually.

2. They e8hi&it co"pleteMeissner effect I.e they areco"pletely dia"agnetic

They do not e8hi&it co"plete Meissnereffect

5. There is only one critical"agnetic field (H C)

There are t#o critical "agnetic field (H C) ielo#er critical field (H C$) and upper criticalfield (H C2)

/. 6o "i8ed state e8ists. Mi8ed state is present.

1. They are called soft superconductors.

They are called Hard super conductors.

4. ;8> lead! tin! Hg etc.! ;8F 6&0Sn! 6&07r! 6&0Ti etc.!


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HighHigh T T C C Super conductors.Super conductors.In a super conductor if the transition te"perature is high ie.!greater than 2: !then it is called as high0te"perature super conductors.In $%G4! Muller and Bednor7 discovered high te"pertaure super conductor inCeramics.So"e of the high T C super conductors and their T C values!

S.No High T C Superconductors

T C in K

1. La 1.85 Ba 0.15 CuO 4 3

!. "Ba ! Cu 3O .# #0

3. T$! Ba ! Ca ! Cu 3O 10 1!54. HgBa ! CaCu ! O 133


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HighHigh T T C C Super conductors.Super conductors.


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HighHigh T T C C Super conductors.Super conductors.Crystal structure of Ba 2Cu 5* %08

0 crystal structure is of the product o&tained is related to the cu&ic perovs ite structure.0 Three BCC are placed one a&ove the another.Te distri&ution of ato"s inthe unit cells is as sho#n!Cu ato" at the &ody corners > G8$ G85A5.Ba ato" at t#o &ody centres > $82 A 2.

t ato" at one &ody centre > $8$A$.* at "id0points of edges > $28$ /85A%.


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Applications of Super conductors: Applications of Super conductors:o SQ,I' >

0SQ,I' stands for Super conducting Q,antu" Interference 'evice.0It is an ultra0sensitive instru"ent used to "easure very #ea "agnetic field

of the order of $: 0$/ tesla

pplication>0 SQ,I' can &e used to detect thevariation of very "inute signalsin ter"s of uantu" flu8.0 It can also &e used as storage

device for "agnetic flu8.0SQ,I' is useful in the study of earth

ua es! re"oving para"agnetic i"purities!detection of "agnetic signals fro" the

&rain and heart.


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Applications of Super conductors: Applications of Super conductors:o Cryotron>

0 Cryotron is a "agnetically operated current s#itch.o Magnetic levitation>

0 -hen a super conducting "aterial sho#s the Meissner effect. 'ue tothis effect! super conducting "aterials strongly repel e8ternal "agnets. Thisleads to a levitation effect.

0 -hen a "agnet is placed over a super conductor! it floats. This pheno"enon is no#n as Magnetic +evitation.

0 Magnetic levitated Train(Maglev train)

o dditional applications>0 Super conducting Magnets.0 ;lectrical Machines.0 Po#er ca&les.0 Co"puter "e"ory devices.


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Applications of Super conductors: Applications of Super conductors:


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Super conductors:Super conductors:


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Than you!!Than you!!

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presentation1-090415045351-phpapp01_2.ppt