superconductivity and new superconductors
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SUPERCONDUCTIVITY
&
NEW SUPERCONDUCTORS
PRESENTED BY
SUPRAVAT PRATIHAR
M.Sc. [Final Year]
2015-2016
DEPARTMENT OF CHEMISTRY
C.M.D. P.G. COLLEGE
BILASPUR UNIVERSITY
Superconductors
An element, inter-metallic alloy, or compound that will
conduct electricity without resistance below a certain
temperature, magnetic field, and applied current.
Definition of Superconductor:
1911: discovery of superconductivity
Whilst measuring the resistivity of
“pure” Hg he noticed that the electrical
resistance dropped to zero at 4.2K
Discovered by Kamerlingh Onnes
in 1911 during first low temperature
measurements to liquefy helium
In 1912 he found that the resistive
state is restored in a magnetic field or
at high transport currents
1913
A Brief History of 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, its resistance suddenly disappeared!
In 1933 Walter Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. This phenomenon is known as perfect diamagnetism and is often refe red to as the Meissnereffect.
Since then major developments have been made in both the discovery of higher temperature superconductors as well as progress in the theory of superconductivity. In 1957 the 1st major advancement in the theory was made by American physicists John Bardeen, Leon Cooper, and John Schrieffer. Their Theories of Superconductivity became known as the BCS theory - abbreviated for the first letter of each man's last name - and won them a Nobel prize in 1972. BCS theory explained superconductivity at temperatures close to absolute zero for elements and simple alloys. However, at higher temperatures and with different superconductor systems, the BCS theory has become inadequate to fully explain how superconductivity is occurring.
INTRODUCTION
The electrical resistivity of a metallic conductor decreases
gradually as temperature is lowered due to decrease of
vibrational resistance of atoms. In ordinary conductors,
such as copper or silver, this decrease is limited by
impurities and other defects. Even near absolute zero, a
real sample of a normal conductor shows some resistance.
In a superconductor, the resistance drops abruptly to zero
when the material is cooled below its critical temperature.
An electric current flowing through a loop
of superconducting wire can persist indefinitely with no
power source.
In a normal conductor, an electric current may be visualized
as a fluid of electrons moving across a heavy ionic lattice. The
electrons are constantly colliding with the ions in the lattice,
and during each collision some of the energy carried by the
current is absorbed by the lattice and converted into heat,
which is essentially the vibrational kinetic energy of the lattice
ions. As a result, the energy carried by the current is constantly
being dissipated. This is the phenomenon of electrical
resistance.
The situation is different in a superconductor. In a
conventional superconductor, the electronic fluid cannot be
resolved into individual electrons. Instead, it consists of
bound pairs of electrons known as Cooper pairs. This pairing
is caused by an attractive force between electrons from the
exchange of phonons.
The mechanism of superconduction is well-understood for low-temperature materials
but there is as yet no settled explanation of high-temperature superconductivity.The
central concept of low-temperature superconduction is the existence of a Cooper pair,
a pair of electrons that exists on account of the indirect electron–electron interactions
fostered by the nuclei of the atoms in the lattice. Thus, if one electron is in a particular
region of a solid, the nuclei there move toward it to give a distorted local structure (Fig.
20.68). Because that local distortion is rich in positive charge, it is favourable for a
second electron to join the first. Hence, there is a virtual attraction between the two
electrons, and they move together as a pair. The local distortion can be easily disrupted
by thermal motion of the ions in the solid, so the virtual attraction occurs only at very
low temperatures. A Cooper pair undergoes less scattering than an individual electron
as it travels through the solid because the distortion caused by one electron can attract
back the other electron should it be scattered out of its path in a collision. Because the
Cooper pair is stable against scattering, it can carry charge freely through the solid, and
hence give rise to superconduction. ATKINS’
PHYSICAL
CHEMISTRY.
Page-737
• In 1957, Bardeen, Cooper, and Schrieffer (BCS) theorized that
superconductivity was the result of electrons binding to form particles
called Cooper pairs
• The electrons exchange vibrational lattice energy called phonons which can
result in the electrons becoming attracted to one another
• Recently, antiferromagnetism has been linked to the explanation of high
temperature ceramic superconductivity
• By changing the chemical composition, BaFe2(As1-xPx)2 has been observed
to have an internal magnetic critical point
• As the composition is changed, antiferromagnetism decreases until it
disappears, resulting in superconductivity
(Top) Lattice of an antiferromagnet. The electron spins are
antiparallel, leading to cancellation of the magnetic field.
(Bottom) Cooper pair formation. Electrons bind during
superconductivity and create boson particles called Cooper pairs.
Basic Principles
• Below a critical temperature (Tc), the
resistance of a superconducting material
becomes almost zero causing current to
flow indefinitely and with no power loss
• No voltage difference is needed to
maintain a current.
• Above a current density,
superconductivity is lost in the material.
• A supercurrent can flow across an
insulating junction in what is called the
Josephson Effect. Cooper pairs can do
this due to quantum tunneling Critical temperature, current density, and magnetic field boundary
separating superconducting and normal conducting states.
Superconductivity can only occur within the teardrop figure.
Schematic of the
Josephson Effect; this
effect allows
electrons to jump
through insulators
In superconducting materials, the characteristics of superconductivity
appear when the temperature T is lowered below a critical
temperature Tc. The value of this critical temperature varies from
material to material. Conventional superconductors usually have
critical temperatures ranging from around 20 K to less than 1 K.
Solid mercury, for example, has a critical temperature of 4.2 K. As of
2009, the highest critical temperature found for a conventional
superconductor is 39 K for magnesium diboride (MgB2), although this
material displays enough exotic properties that there is some doubt
about classifying it as a "conventional" superconductor.
Cuprate superconductors can have much higher critical
temperatures: YBa2Cu3O7, one of the first cuprate superconductors to
be discovered, has a critical temperature of 92 K, and mercury-based
cuprates have been found with critical temperatures in excess of
130 K. The explanation for these high critical temperatures remains
unknown. Electron pairing due to phonon exchanges explains
superconductivity in conventional superconductors, but it does not
explain superconductivity in the newer superconductors that have a
very high critical temperature.
Similarly, at a fixed temperature below the critical
temperature, superconducting materials cease to
superconduct when an external magnetic field is applied
which is greater than the critical magnetic field. This is
because the Gibbs free energy of the superconducting
phase increases quadratically with the magnetic field while
the free energy of the normal phase is roughly independent
of the magnetic field. If the material superconducts in the
absence of a field, then the superconducting phase free
energy is lower than that of the normal phase and so for
some finite value of the magnetic field (proportional to the
square root of the difference of the free energies at zero
magnetic field) the two free energies will be equal and a
phase transition to the normal phase will occur.
Comparison of superconductor
and standard conductor in a
magnetic field. The
superconductor excludes itself
from the field while the field
passes through the conductor.
Superconductor Conductor
• The phenomena of expelling magnetic flux
experienced by superconductors is called
the Meissner Effect.
• The Meissner Effect can be understood as
perfect diamagnetism, where the magnetic
moment of the material cancels the external
field or M = - H.
• The critical field and temperature are
interdependent through:
Bc= B0[1-(T/Tc)2 ]
1933: Meissner-Ochsenfeld effect
Ideal conductor! Ideal diamagnetic!
Meissner effect
When a superconductor is placed in a weak
external magnetic field H, and cooled below its
transition temperature, the magnetic field is ejected. The
Meissner effect does not cause the field to be
completely ejected but instead the field penetrates the
superconductor but only to a very small distance,
characterized by a parameter λ, called the London
penetration depth, decaying exponentially to zero within
the bulk of the material. The Meissner effect is a
defining characteristic of superconductivity. For most
superconductors, the London penetration depth is on the
order of 100 nm.
• The strange magnetic
properties created by
superconductors can cause the
material to levitate in place
over a magnet
• The superconductor will
remain a certain distance from
the magnet but will not flip
over or reorient
• This video demonstrates this
phenomena and potential for
levitation applications
http://www.youtube.com/watch?v=6lmtbLu5nxw
Critical Temperatures of Conducting Materials• In most metals such as titanium,
copper, or lead, resistivity decreases
as temperature decreases
• However, the resistivity suddenly
drops to near zero at a critical
temperature (Tc)
• Metals and metal alloys have a
critical temperature of less than
about 20 K, which is extremely low
and difficult to achieve.
• Yttrium Barium Copper Oxide
(YBCO) has a critical temperature
of 92 K and others are even higher.
These temperatures can be achieved
by utilizing liquid nitrogen, a
relatively cheap coolant.
• Some metals become superconductors at extremely
low temperatures
• Some of these include mercury, lead, tin, aluminum,
lead, niobium, cadmium, gallium, zinc, and
zirconium
• Unfortunately, the critical temperatures are too low
for practical application
• For example, Aluminum has a Tc of only 1.20K,
nearly impossible to reach by conventional methods
Aluminum tubing can become
superconductive at very low
temperatures.http://www.globalmetals.com/aluminum-
tubestubing.html
Fig. 12.2: Lead can also become superconductive at low
temperatures.http://39clues.wikia.com/wiki/Lead
High-temperature superconductors (abbreviated high-Tc or HTS) are
materials that behave as superconductors at unusually high temperatures.
The first high-Tc superconductor was discovered in 1986 by IBM
researchers Georg Bednorz and K. Alex Müller,who were awarded the
1987 Nobel Prize in Physics "for their important break-through in the
discovery of superconductivity in ceramic materials".
Whereas "ordinary" or metallic superconductors usually have transition
temperatures (temperatures below which they superconduct) below 30 K
(−243.2 °C), HTS have been observed with transition temperatures as high
as 138 K (−135 °C). Until 2008, only certain compounds of copper and
oxygen (so-called "cuprates") were believed to have HTS properties, and
the term high-temperature superconductor was used interchangeably with
cuprate superconductor for compounds such as bismuth strontium
calcium copper oxide (BSCCO) and yttrium barium copper oxide
(YBCO). However, several iron-based compounds (the iron pnictides) are
now known to be superconducting at high temperatures.
High-temperature
superconductivity
YBa2Cu307
Discovered: 1987 by Paul Chu
Tc: 90-95K
Bc2: 100 Tesla at 77 K
Jc: 1.0x109 A/m2 at 77 K
Referred to as “1-2-3” superconductor
because of the ratio of the three metallic
elements
Type: Type II Ceramic
YBaCuO superconductors
• Yttrium Barium Copper Oxide was the first
superconductor developed with a Tc above the
boiling point of Nitrogen (Tc=90 K).
• Thallium Barium Calcium Copper Oxide has
the highest Tc out of all superconductors
(Tc=125 K)
• Copper Oxides are believed to be good
superconductors partly due to the Jahn-Teller
effect, which causes the 2 oxygens on opposite
sites of the octahedron to be farther from the
copper than the other 4 oxygens of the
octahedron.
• This suggests that the electrons interact
strongly with the positions of copper and
oxygen in the lattice (Cooper pair).
• Antiferromagnetism must be eliminated for
superconductivity to appear.
CopperIron
Cava, J.R. Sci. Amer. 1990.
(top): Illustration of a ceramic lattice. The Jahn-Teller
effect causes the superconductivity here.
(bottom): Levitation caused by the interactions of
electrons and oxygen, and therefore superconductivity.
Fig : Other copper oxides that are also superconducting. These ceramics show potential for applications.
For industrial setting, the toxicity of the materials should be considered. Cava, J.R. Sci. Amer. 1990.
Atypical Superconductors
and the Future
As if ceramic superconductors were not strange enough, even more
mysterious superconducting systems have been discovered. One is based on
compounds centered around the "Fullerene". The fullerene name comes from
the late designer-author Buckminster Fuller. Fuller was the inventor of the
geodesic dome, a structure with a soccer ball shape. The fullerene - also called
a buckminsterfullerene or "buckyball" - exists on a molecular level when 60
carbon atoms join in a closed sphere. When doped with one or more alkali
metals the fullerene becomes a "fulleride" and has produced Tc's ranging
from 8 K for Na2Rb0.5Cs0.5C60 up to 40 K for Cs3C60. In 1993 researchers at the
State University of New York at Buffalo reported Tc's between 60 K and 70 K
forC-60 doped with the interhalogen compound ICl.
Fullerenes, like ceramic superconductors, are a fairly recent discovery. In
1985, professors Robert F. Curl, Jr. and Richard E. Smalley of Rice University
in Houston and Professor Sir Harold W. Kroto of the University of Sussex in
Brighton, England, accidentally stumbled upon them. The discovery of
superconducting alkali metal fullerides came in 1991 when Robert Haddon
and Bell Labs announced that K3C60 had been found to superconduct at 18 K.
ORGANIC SUPERCONDUCTORS
"Organic" superconductors are part of the organic conductor family which includes:
molecular salts, polymers and pure carbon systems (including carbon nanotubes and
C60 compounds). The molecular salts within this family are large organic molecules that
exhibit superconductive properties at very low temperatures. For this reason they are often
referred to as "molecular" superconductors. Their existence was theorized in 1964 by Bill
Little of Stanford University. But the first organic superconductor (TMTSF)2PF6 was not
actually synthesized until 1980 by Danish researcher Klaus Bechgaard of the University of
Copenhagen and French team members D. Jerome, A. Mazaud, and M. Ribault. About 50
organic superconductors have since been found with Tc's extending from 0.4 K to near 12 K
(at ambient pressure). Since these Tc's are in the range of Type 1 superconductors, engineers
have yet to find a practical application for them. However, their rather unusual properties
have made them the focus of intense research. These properties include giant
magnetoresistance, rapid oscillations, quantum hall effect, and more (similar to the behavior
of InAs and InSb). In early 1997, it was, in fact (TMTSF)2PF6 that a research team at SUNY
discovered could resist "quenching" up to a magnetic field strength of 6 tesla. Ordinarily,
magnetic fields a fraction as strong will completely kill superconductivity in a material.
Organic superconductors are composed of an electron donor (the planar organic molecule)
and an electron acceptor (a non-organic anion).
Superconducting Properties of Ag and Sb Substitution
on Low-Density YBa2Cu3Oδ
• Different concentrations of Silver (Ag) and Lead (Sb)
were introduced as impurities into a YBCO ceramic
compound
• It was found that the addition of Ag at an optimum
concentration enhanced both the critical temperature
and current density of YBCO. Above and below this
concentration the properties diminished
• Sb impurities did not affect the superconducting
properties of the YBCO ceramic.
• As impurities of Ag and Pb were added to YBCO, the
transition temperature range, delta Tc was affected
• The correlation between concentration of Ag or Pb
versus transition temperature difference appeared to be
random
Azhan, F.; et al. J. Supercond. Nov. Magn. 2013, 26, 921-935.
http://www.kreynet.de/asc/ybco.html
Silver (Ag)
Lead (Pb)
Figure : Adding Ag and Pb impurities to the
lattice structure of YBCO can alter its
superconductive properties slightly.
• Superconductors have potential to create a new
variety of electrical and magnetic technologies
• Superconductors will need to be improved by
researching and synthesizing a ceramic
superconductor with a high critical temperature value
• By doing this, either minimum cooling, or no
cooling at all would be needed to create
superconductive properties in the material
• For example, YBCO only requires liquid
nitrogen for cooling. Conventional freezers could
be used if the Tc could be increased to around
190 K
• Since superconductors can be applied without
solid understanding of the theory behind it, they
are an attractive materialHgBa2Ca2Cu3Ox
Figure : Applied Magnetic
Field vs Critical Temperature.
As the critical temperature
increases, the applied magnetic
field decreases.
Flukiger, R. Rev. Accel. Sci. Tech. 2012, 5, 1-23.
Patel, M.J. et. al. Nat. Confer. Rec. Trend. Engr. Tech. 2011.
• If a high critical temperature
superconductor is developed that has a
critical temperature that is higher than
HBCCO (133 K), more practical
applications will become feasible
• Electrical power transmission through
superconducting materials and wire
o Low power loss
o Low voltage required for high
current
o Utilizes less physical space
• Computer signal transmission
o Low resistivity allows for
computing speed to increase
greatly
http://gigaom.com/2010/10/06/superconducting-wire-powering-up-korean-smart-grid/
Power lines demonstrating the great reduction of
space needed by utilizing superconducting wire
rather than standard cables.
Figure : Example of a superconducting cable. The liquid nitrogen
coolant is part of the cable in order to keep the superconductor wire
below the critical temperature. These cables can greatly reduce the
physical space needed in our electrical infrastructure.
• Some applications are used today:
o Magnetic Resonance Imaging
o Nuclear Magnetic Resonance
Spectroscopy
• Future applications can benefit from
interesting magnetic properties displayed
by superconductors
• Particle Accelerators
• Magnetic Levitation
o High-Speed Magnetic Levitation
Trains for mass transport
o By utilizing levitation, friction
between the train and the track is
eliminated
o This can allow trains to increase
their speed dramatically
Figure :(top/middle): MRI
scanners currently utilize
superconductors.
Figure :(bottom): Mag-Lev train
demonstrating the potential of using
superconductors in mass-transport.
•Particle Accelerators
•Generators
•Transportation
•Power Transmission
•Electric Motors
•Military
•Computing
•Medical
•B Field Detection (SQUIDS)
The Yamanashi MLX01 MagLev train
Application of
Superconductors
MAGLEV TRAIN:Maglev (derived from magnetic levitation) is a
transport method that uses magnetic levitation to move
vehicles without touching the ground. With maglev, a
vehicle travels along a guideway using magnets to
create both lift and propulsion, thereby reducing
friction by a great extent and allowing very high
speeds.
The Shanghai Maglev Train, also known as
the Transrapid, is the fastest commercial train currently
in operation and has a top speed of 430 km/h
(270 mph). The line was designed to connect Shanghai
Pudong International Airport and the outskirts of
central Pudong, Shanghai. It covers a distance of 30.5
kilometres in 8 minutes.
The linear motor car experiment vehicles MLX01-01 of Central Japan Railway
Company. The technology has the potential to exceed 4000 mph (6437 km/h) if
deployed in an evacuated tunnel.
MAGLEV: flying train
Shanghai Maglev Train (SMT)
Superconducting RF cavities for colliders
The Large Hadron Collider | CERN
Energy transmission
Powerful superconducting magnets
Scientific and industrial NMR facilities
900 MHz superconductive
NMR installation. It is used
For pharmacological
investigations of various
bio-macromolecules.
Yokohama City University
BRUKER AEON-1GHz
NEXTGEN NMR
Medical NMR tomography equipment
G scan - an Open Standing MRI scanner
Superconducting Magnets to Protect Spacecraft
from Radiation:While on Earth, the planet protects us from space radiation
and cosmic rays with its magnetic field. NASA scientists are
now working on an analogous approach to protect spacecraft
from space radiation outside of Earth’s protective envelope.
NASA along with its partners is exploring the possibility of
using superconducting magnets to generate magnetic fields
around space probes and space habitats to protect them from
space radiation and cosmic rays.
A Superconducting E-bomb (EMP BOMB):
"The U.S. Air Force has hit Iraqi TV with an experimental
electronmagetic pulse device called the 'E-Bomb' in an attempt to knock
it off the air and shut down Saddam Hussein's propaganda machine. Iraqi
satellite TV, which broadcasts 24 hours a day outside Iraq, went off the
air around 4:30 a.m. local time."
- CBS News, 3-25-03
E-bombs can unleash in a flash as much electrical power 2 billion watts
or more as the Hoover Dam generates in 24 hours. [And], although the
Pentagon prefers not to use experimental weapons on the battlefield, "the
world intervenes from time to time," - Defense Secretary Donald
Rumsfeld.
- Time Magazine, 1-19-03
An e-bomb (electromagnetic bomb) is a weapon that uses an
intense electromagnetic field to create a brief pulse
of energy that affects electronic circuitry without harming
humans or buildings. At low levels, the pulse temporarily
disables electronics systems; mid-range levels corrupt
computer data. Very high levels completely destroy
electronic circuitry, thus disabling any type of machine that
uses electricity, including computers, radios, and ignition
systems in vehicles.
ELECTROMAGNETIC PULSE WEAPONS CAN DISABLE
ALL ELECTRONIC EQUIPMENTS INSIDE THE RANGE:
A directed-energy weapon (DEW) emits highly focused
energy or EMP, transferring that energy to a target to damage
it.
Potential applications of this technology include anti-
personnel weapon systems, potential missile defence system,
and the disabling of lightly armored vehicles such as cars,
drones, jet skis, and electronic devices such as mobile
phones.
• Superconductivity is a state of thermodynamical equilibrium where the
electrical resistance is 0 and that is achieved at near 0 K temperatures
• External magnetic flux is expelled from the superconductor in what is
called the Meissner effect. The application of an external magnetic flux
also lowers the critical temperature at which superconductivity is
achieved. After a critical flux, superconductivity can no longer be
achieved
• Using superconducting materials in circuit elements would mean zero
power loss due to resistance. Also, no voltage difference would be
needed to maintain the current.
• Adding impurities to ceramic superconductors can alter the critical
temperature and critical current density
• Superconducting ceramic materials have shown the most promise for
future technologies because of their relatively high critical temperatures
• The underlying principles of superconductivity are explained through
an interactive attraction between electrons (Cooper pair) and their
interaction with lattice vibrations (phonons).
Figure : Structural
interpretation of a
ceramic superconductor.
Notice how there are
layers of molecules
sandwiched between
others.
http://physics.aps.org/story/v9/st12
IMPORTANT SOURCES:
Research Groups and Institutions:
•Kamerlingh Onnes Laboratory | Leiden University - Netherlands
•Superconductivity and Magnetism | Argonne National Labs
•Superconducting Stripes | La Sapienza University - Italy
•Superconductivity Group | University of Rome - Italy
•Superconductivity Group at UiO | University of Oslo - Norway
•Superconductivity Group | University of Durham - UK
•Rapid Single-Flux Quantum Laboratory | State University of New York
•DHV Research Group | University of Illinois at Urbana-Champaign
•Texas Center for Superconductivity | University of Houston
•The Lemberger Superconductivity Lab | Ohio State Univ.
•Institute for Superconducting and Electronic Materials | Australia
•Quantum Chaos and Superconductivity | Northeastern University
•Bar-Ilan Institute of Superconductivity | Israel
•Weizmann Institute of Science | Superconductivity Group - Israel
•A S T R A | Applied Superconductivity & Training - Slovakia
•B. Verkin Institute for Low Temperature Physics and Engineering | Ukraine
•AIST | National Institute of Advanced Industrial Science and Technology - Japan
•Nanoscale Superconductivity and Magnetism | University of Leuven - Belgium
Manufacturers/Industry:
CAN Superconductors | HTS Bulk
Superconductors for Practical Applications
SuperPower, Inc. | Developer and Producer of 2G
HT Superconducting Wire
Star Cryoelectronics | Thin Film, Squid, and
Biomedical Products
ATKINS’ PHYSICAL CHEMISTRY, Eighth Edition. Peter Atkins, Julio
de Paula.
Physical Chemistry (Third Edition). Robert G. Mortimer.
Cava, J.R.; Superconductors and beyond 1-2-3. Scientific American 1990.
http://www.superconductors.org/
https://en.wikipedia.org/wiki/Superconductivity
Flukiger, R. Overview of Superconductivity and Challenges in
Applications. Reviews of Accelerator Science and Technology. 2012, 5, 1-
23.
Patel, M.J.; Agrawal, D.H.; Pathan, A.M. Review on Superconductivity:
The Phenomenon Occurred at Low Temperature. National Conferences on
Recent Trends in Engineering & Technology. 2011.
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