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SUPERCONDUCTIVIT Y

Superconductivity 1

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Page 1: Superconductivity 1

SUPERCONDUCTIVITY

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• Superconductivity was first discovered by Kamerlingh Onnes (1911.)

• First successful assembly of phenomenological equations made for superconductive metals - F. London (1935.)

• 1925. Einstein predicts special condensation of Bose-Einstein gas – a pair of fermione can be combined to give bosons (known since 1931.)

• 1950. F. London compiled all known ideas about superconductivity in a book “Superfluids” vol.1.

• BCS theorie (Bardeen et al. ), 1957. – first succsesful theorie which explains microscopic mechanism of superconductivity in metals and alloys

Introduction

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• Practical usage has increase but you stll need to cool down material to become superconducting

• Superconducting magnets are used in particle accelerators are cooled on 4K (He)- very rare and very expensive gas but using liquid nitrogen you can cooled down materials at T > 77K

• BCS ( John Bardeen, Leon Cooper, and Robert Schrieffer) theorie ca t explain all kind of behaviour nof superconductivity – type II. Superconductors

• The BCS theorie tells us that electrons in metals are paired by exchainging phonons

• Other theories replace phonons with other bosons : plasmons, excitons and magnons (Canright & Vignale , 1989, Tachiki &i Takahashi 1988, Takada 1993).

Introduction

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• Coling down mercury below 4.1 K shows superconductivity - (Onnes) – zero electrical resistivity

• Other parametres are necesary like magnetic field (H) and electricity (I) –need to be below critical values

Superconductivity

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• Levitation of superconductor in magnetic field – causes Meissner efect

• Induced electrisity in superconductors causes induced magnetic field with different magnetic moment from outer magnetic moment

Superconductivity

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Superconductivity

Picture 1.Levitation of magnet above superconductor ,with permission from wikipedia. org

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Superconductivity

Picture 2. Meissner efect

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• BCS theorie – lost of electrical resistance creating electric pairs called Cooper pairs

• 1986. discovery of superconductors with high critical temperature

• Transformation of material from one phase to another leads to sudden change in resistivity of materials , transfomation doesnt occur in a form of changing inner structure or chemical change

Superconductivity

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Superconductivity Material K

galium 1.1

aluminum 1.2

indium 3.4

tin 3.7

Lead 0

niobium 9.3

La-Ba-Cu oxide 17.9

Y-Ba-Cu oxide 92

Tl-Ba-Cu oxide 125

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Types of superconductors • Type I. Superconductors • Have:zero electrical resistivity below critical temp., zero

internal magnetic field (Meissner efect), and crtitical magnetic field causing superconductivity

• 27 pure metals – behaviour can be explained with BCS theorie

• Metals which shows excellent electrical conductivity doesnt shows superconductivity - the smallest vibrations of crystall lattice –not enough Cooper pairs (gold, silver and copper )

• Type II. Superconductors

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Types of superconductors Material Tc(K)

Rh 0

W 0,015

Be 0,026

Ir 0,1

Lu 0,1

Hf 0,1

Ru 0,5

Os 0,7

Mo 0,92

Zr 0,546

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Vrste supravodiča Material Tc(K)

Cd 0,56

U 0,2

Ti 0,39

Zn 0,85

Ga 1,083

Gd 1,1

Al 1,2

Pa 1.4

Th 1,4

Re 1,4

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Vrste supravodiča

Material Tc(K)

Tl 2.39

In 3,408

Sn 3,722

Hg 4,153

Ta 4,47

La 6,00

Pb 7.193

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Types of superconductors

Type II. Superconductors • materials that shows better characteristics than type

I. Superconductors • Have higher critical magnetic fields • Have mixed magnetic conditions –vortex state

which are repulsive towards applied outside magnetic field

• NbTi – used for production of superconducting magnets

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Types of superconductors Material Transformation temp.K Critical field (T)

NbTi 10 15

PbMoS 14,4 6,0

V3Ga 14,8 2,1

NbN 15,7 1,5

VSi 16,9 2,35

Nb3Sn 18,0 24,5

Nb3Al 18,7 32,4

Nb3(AlGe) 20,7 44

Nb3Ge 23,2 38

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Superconductivity

• The new ones : magnesium diboride and plutonium compounds (search for on ScienceDirect)

• 1993. Schilling & Cantoni, proved experimentally the highest achieved Tc 135 K , under 1 atm, for system

Hg-Ba-Ca-Cu-O –but the temp. can rise above 180 K using higher pressure

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Experimental part

• Performed on Institute Ruđer Bošković (Zagreb) with help of dipl.ing Lidija Androš

• 2BaCO3 + 3CuO + ½ Y2O3 = YBa2Cu307-δ

• Total mass of sample 2 g, means:• 1,0570 g BaCO3

• 0,6390 g CuO• 0,3025 g Y203

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Experimental part • We made 2 pastilles and put them in owen :• 1.phase : 900 °C - 480 minutes • 900 °C – 600 min• 2.phase : 930 °C - 480 min• 930 °C - 600 min • 3.phase with oxygen : 8 h on 950 °C,

16 h on 950 °C, 5h on 420 °C, 6h on 420 °C, 5h on 20 °C

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Usage - Magnets - Mass spectrophotometers - Particle acclerators - SQUID(superconducting quantum interference devices)- Energy transfer , transformators and acumulators - TGV – Maglev trains

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Literature ;- ScienceDaily: Physicist Discovers Exotic Superconductivity - Hyperphysics stranica for BCS and Meissner efect –http://hyperphysics.phy- http://ffden-2.phys.uaf.edu• SUPERCONDUCTIVITY– THEORY AND APPLICATIONS , Adir Moysés Luiz, INTECHweb.org,

Rijeka, Croatia , 2011• www.superconductors.org