Superconductors and NANOTECHNOLOGY

1/23/2017 1Dr A K Mishra, Academic Coordinator, JIT Jahangirabad

Engineering Physics II Unit V

Presentation By

Dr.A.K.Mishra

Associate Professor

Jahangirabad Institute of Technology, Barabanki

Email: [email protected]

[email protected]

Superconductors• 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.

• Later, in 1913, he won a Nobel Prize in physics for his research in this area.

• Superconductors, materials that have no resistance to the flow of electricity, are one of the last great frontiers of scientific discovery

• At the critical temprature the resistance falls to zero

1/23/2017 Dr A K Mishra, Academic Coordinator, JIT Jahangirabad 2

Continued……………..

• These can be used to make low loss power line and very good electromagnets.


Temperature (K)

Resis

tanc

e

T C

O

Temperature (K)

Resis

tanc

e

4.0 4.1 4.2 4.3 4.40.0

1.0

1.5

Temperature dependence of resistivity in superconducting materials

• Superconductivity in the metal are depend on the intensity of the field and temperature.

• to maintain the Superconductivity both the parameter should be less than their critical values.

1/23/2017Dr A K Mishra, Academic Coordinator,

JIT Jahangirabad 4

Normal MetalSuperconductor

Tc00


• The dependence of the temperature on magnetic field can be represented by following equation,

• Where Hc is the critical field strength, Hc(0) is the maximum field strength at absolute zero and Tc is the critical temperature. it is clear from the fig the temperature below Tc the materials remains in the superconducting state till a corresponding critical magnetic field is applied when the field is higher than the Hc the superconducting state is destroyed and the materials comes to its normal state.


]c

-Hc(0)[1 = HcTT

2

Meissner Effect (Effect of magnetic field)

• When a material makes transition from normal to superconducting state, it excludes magnetic field from its interior.

• This phenomenon is called the meissner effect.• Meissner and Ochsenfield (1953) concluded that when

superconductor is cooled in longitudinal magnetic field,thenabove its transition temperature magnetic lines pass through specimen but below transition temperature the magnetic flux is pushed out of the specimen,this indicates that below Tc the metal become perfectely diamagnetic.

• Thus phenomenon of exclusion of magnetic flux from the interior of a superconductor below Tc is the Meissner effect.


Continued…………


Below Tc a persistence current generates on the surface and cancel the flux density inside the superconductor.Thus for a superconducting state,if B is zero inside the specimen then we get,



tyconductivi is WhereE = J

law Ohms from Nowc.diamagnetiperfect a is state ctingsupercondu hence

metal, cdiamagneti theofcondition theis This

1 - =HM = lity,susceptibi Magnetic

H - = M

M) + (H = 0

M) + (H = B

0

0



0 = E i.e., (J)density current infinitefor zero bemust field electric zero, becomes

)(y resistivitequation above fromclear isIt J = E

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ctor.supercondu a of properties essential andt independen two theare smdiamagneti

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0 = E puttingBy tB - = E X

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Persistent current

• when an electric current is set in a superconductor it can persist for long time without any e.m.f.

• An induced current can flow in a ring of superconducting material by cooling it in the presence of magnetic field below Tc and then remove the field (fig A),the flux outside the ring disappears but it remains inside the ring (fig B).


TYPE OF SUPERCONDUCTORS• Superconductors are divided in to two parts depending on the

mechanism from superconducting state to normal state due to exceed of critical field.TYPE I SUPERCONDUCTORS OR SOFT SUPERCONDUCTOR

• Type 1 superconductors - characterized as the "soft" superconductors - were discovered first and require the coldest temperatures to become superconductive.

• They exhibit a very sharp transition to a superconducting state and "perfect" diamagnetism - the ability to repel a magnetic field completely.

• Type 1 superconductors along with the critical transition temperature (known as Tc) below which each superconducts.


Continued………..• Surprisingly, copper, silver and gold, three of the best metallic

conductors, do not rank among the superconductive elements.

For type I superconductormagnetic flux is expelledproducing magnetization

with increasing field untilis reached, at which it

falls to zero with a normal conductor.


Applied Magnetic field (H)

Mag

netiz

atio

n (M

)

H C

I Type

HC

Mag

netiz

atio

n (M

)

H C

I Type

TYPE II SUPERCONDUCTORS OR Hard SUPERCONDUCTOR

• Except for the elements vanadium, technetium and niobium, the Type 2 category of superconductors is comprised of metallic compounds and alloys.

• Type II have two criticalfield ( & )below behave astype I and above behave as normal conductor.


Mag

netiz

atio

n (M

)

H C

II Type

HC1HC2

HC1HC2

HC1

HC2

Continued…………..• This new category of superconductors was identified by L.V.

Shubnikov at the Kharkov Institute of Science and Technology in the Ukraine in 1936(1) when he found two distinct critical magnetic fields (known as Hc1 and Hc2) in PbTl2.

• The first of the oxide superconductors was created in 1973 by DuPont researcher Art Sleight when Ba(Pb,Bi)O3 was found to have a Tc of 13K.

• Type 2 superconductors - also known as the "hard" superconductors - differ from Type 1 in that their transition from a normal to a superconducting state is gradual across a region of "mixed state" behavior. Since a Type 2 will allow some penetration by an external magnetic field into its surface.


London Penetration depth• According to F.London and H.London,the magnetic field at the

surface of a superconductor does not vanish suddenly but decays exponentially to zero according to following equation,

Where H0 is the field at the surface, x is the distance from the surface and λ is the characteristics length known as London penetration depth.


ex

H0 = H

Continued………….• The magnetic field at the surface of the superconductor

decays to at a distance in the interior of superconductor.


eB 0

x

0 x

x

B0

B

eB-x

0 (x) B

BCS THEORY• The first widely accepted quantum mechanical explanation of

superconductivity was presented by J.Barden, L N Copper and John Schriffer (BCS) in 1957.

• This theory based on the electron-electron interaction via phonon as a mediator.

• Under certain restricted conditions, the electron couple together electron-lattice electron interactions.

• Therefore, the electron and phonon interaction is the basic mechanism responsible for superconductivity.


Continued………….

• Atoms in a crystal lattice are constantly vibrating. Because they are all connected, these vibrating atoms create waves throughout the metal.

• These waves are called phonons.• The more the atoms are vibrating (ie. the hotter the material),

the larger the phonons.• In superconductors (at low temperatures) the phonons are

small, and any distortion caused by the electrons is reflected in phonons.

• These phonons can attract electrons to form cooper pairs.


Continued………….• As shown below the moving electron causes the lattice to

distort and an increased positive charged density is formed near the electron.


Continued………….• To counter-act this a second electron is attracted towards the

electron (even though the two electrons repel).

• This pair of electrons are called a Cooper pair, which move easily through the material.

• This is because their strong negative charge will repel any positive atoms that it gets close to, thus no collisions occur and electron flow is not resisted.


Applications of Superconductivity• The early superconductors were chunks of metal. A breakthrough came in

the 1960s with the development of a superconducting wire, an alloy of niobium and titanium. With this wire, engineers could wind electromagnet coils. These superconducting coils permit the construction of extremely powerful electromagnets. As with many engineering advances, there are tradeoffs:

Cost Saving: Since the magnet is operated with the wire at superconducting temperatures, the resistance of the coils is zero and no energy is lost to heating the coils. For superconducting magnets, a small power supply is sufficient to initiate the flow of current.

• Cost Increase: Since the coils must be maintained at a low temperature, an expensive liquid helium refrigeration system is required. The superconducting magnet coils produce a large and uniform magnetic field inside the patient's body. Note the large size of the scanner, which contains the liquid helium refrigeration system.


• Maglev Train• To minimize friction, powerful onboard superconducting magnets

support this train above the tracks.• The train reached a speed of 411 km/hr (256 mi/hr). Running

alongside the track are walls (see photo) with a continuous series of vertical coils of wire mounted inside.

• The wire in these coils is not a superconductor. As the train passes each coil, the motion of the superconducting magnet on the train induces a current in these coils, making them electromagnets.

• The electromagnets on the train and outside produce forces that levitate the train and keep it centered above the track.

• In addition, a wave of electric current sweeps down these outside coils and propels the train forward .


NANOTECHNOLOGY• Nanotechnology is the engineering of functional systems at

the molecular scale. 'nanotechnology' refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, high performance products.

• Nanomaterials can be fabricated in two ways, top down and bottom up. In top down nonmaterial's are constructed by removing existing materials from larger entities. This is used in manufacturing microprocessors. In bottom up, materials are built up atom by atom or molecule by molecule. This approach is more time consuming therefore self assembly process is usually employed so that atoms spontaneously arrange themselves into final product.


Properties of nanomaterial's

• Nanomaterials have the following properties:• They are very hard.• They are ductile at high temperatures.• They are chemically very active.• They are exponentially strong.• Category of nanomaterials:• Fullerences• Nanoparticles• Fullerences:The third form of carbon was discovered in 1985.it is cluster of

60 carbon atoms like a football.• Buckministerfullerence the name was given by the architect R.

Buckministerfuller.


Continued……….

• it has carbon atoms at 60 chemically equivalent vertices, which are connected by 32 faces,12 of which are pentagons and 20 hexagons.

• These are allotrops of carbon which are basically grapheme sheets rolled into tubes or spheres,Graphene is a one atom thick layer of graphite.

• Buckminister C60 is also known as buckyboll,is the smallest member of the fullerence family. Carbonnanotube (CNT) are also member of this family.


Continued……….

• Fullerene are produced by sending large current between two nearby graphite electrodes.

Referred from Google image


Continued……….

• this results into carbon plasma arc between electrodes, which gives fullerence on cooling.

• Buckminsterfullerene C60, also known as the buckyball, is a representative member of the carbon structures known as fullerenes.

• Members of the fullerene family are a major subject of research falling under the nanotechnology umbrella.


Production of Buckyballs

• Buckyballs can be produced by vaporizing carbon placed between two carbon electrodes.

• when electric arc is produced between electrodes placed in the vicinity of each other in a low pressure reaction chamber,buckyballs generated along the carbon.

• They can be separated with the help of solvent like benzene.


Properties of Buckyballs• Buckyballs can be used in many applications

because of their unusual hollow structure.• Buckyballs are extremely stable, and can bear

very high temperature and pressure.• Even after reaction with other atoms and

molecules, their stable spherical structure remains intact.

• Addition of other molecules at the outside and trapping of smaller molecules inside a buckyballcreates new molecule.


Uses of Buckyballs• Buckyballs becomes a superconductor when dopped with a

little amount of potassium or cesium.this is the best superconductor known to us.

• Buckyballs can better storage of hydrogen because when the C60 molecules absorb one molecule of hydrogen, its structure does not disrupt.

• Bucky balls can deliver drugs directly to the infected region of the body, they also have the ability to act as antioxidants, thereby counteracting free radicals in the human body.

• Anti- ageing and anti-wrinkle creams are being manufactured by using buck balls.

• Bucky balls are also used as cutting tools.


Carbon Nano tubes (CNTs)• Carbon nanotubes were first discovered by Somio

Iijima in 1991. cnt belongs to the family of graphite.

• the structure of graphite is one-atom thick planar network of interconnected hexagonal ring of carbon atoms.

• these sheets of carbon are staked on the top of one another such that they are able to slide over each other. This is responsible for the softness of graphite; hence graphite can be used as a lubricant.



• When graphite sheets are rolled into cylinder and their edges are joined they form carbon nanotubes.

What is a Carbon Nanotube:A Carbon Nanotube is a tube-shaped material, made of carbon, having a diameter measuring on the nanometer scale. A nanometer is one-billionth of a meter, or about one ten-thousandth of the thickness of a human hair. The graphite layer appears somewhat like a rolled-up chicken wire with a continuous unbroken hexagonal mesh and carbon molecules at the apexes of the hexagons.


Continued……………..• Carbon Nanotubes have many structures, differing in

length, thickness, and in the type of helicity and number of layers. Although they are formed from essentially the same graphite sheet, their electrical characteristics differ depending on these variations, acting either as metals or as semiconductors.

• As a group, Carbon Nanotubes typically have diameters ranging from <1 nm up to 50 nm. Their lengths are typically several microns, but recent advancements have made the nanotubes much longer, and measured in centimeters.


Continued……………

• Carbon Nanotubes can be categorized by their structures.

• Single-wall Nanotubes (SWNT)• Multi-wall Nanotubes (MWNT)• Double-wall Nanotubes (DWNT)• What are the Properties of a Carbon

Nanotube?



• The intrinsic mechanical and transport properties of Carbon Nanotubes make them the ultimate carbon fibers. Overall, Carbon Nanotubes show a unique combination of stiffness, strength, and tenacity compared to other fiber materials which usually lack one or more of these properties. Thermal and electrical conductivity are also very high, and comparable to other conductive materials.

• What are the Potential Applications for Carbon Nanotubes?Carbon Nanotube Technology can be used for a wide range of new and existing applications:


Continued………….• Conductive plastics • Structural composite materials • Flat-panel displays • Gas storage • Antifouling paint • Micro- and nano-electronics • Radar-absorbing coating • Technical textiles • Ultra-capacitors • Atomic Force Microscope (AFM) tips • Batteries with improved lifetime • Biosensors for harmful gases • Extra strong fibers



• Nanocyl uses the "Catalytic Carbon Vapor Deposition" method for producing Carbon Nanotube Technologies. This proven industrial process is well known for its reliability and scalability. It involves growing nanotubes on substrates, thus enabling uniform, large-scale production of the highest-quality carbon nanotubes worldwide.
