2. What is superconductivity?
Superconductivity is a phenomenon of exactly
zero electrical resistance and expulsion
of magnetic fields occurring in
certain materials when cooled below a
characteristic critical temperature.
It was discovered by Dutch
physicist Heike Kamerlingh
Onnes on April 8,1911 in
Leiden.
3.
4. Meissner Effect
When a material makes the
transition from the normal
to superconducting state, it
actively excludes magnetic
fields from its interior.
It was discovered by German
physicists Walther
Meissner and Robert
Ochsenfeld .
6. The BCS Theory
Electron-Lattice Interactions
A passing electron attracts the lattice, causing a slight ripple toward its path.
Another electron passing in the opposite direction is attracted to that
displacement.
BCS theory suggests that superconductors have zero electrical resistance
below critical temperatures because at such temperatures the electrons pass
unhindered through the crystal lattice and therefore lose energy. The theory
states that the supercurrent in a superconductor is carried by many million
bound electron pairs, called Cooper Pairs.
7.
8.
9. High TC Super conductors.
In a super conductor if the transition temperature is high ie.,greater
than 20K, then it is called as high-temperature super conductors.
In 1986, Muller and Bednorz discovered high tempertaure super
conductor in Ceramics.
11. Metal and Alloys
• 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
• Metal alloys like Nb-Ti, and Nb-Zr are
usually Type II superconductors
• Metal Alloys have higher critical
temperatures and magnetic fluxes than
pure metals.
• As a consequence of their properties,
they are more useful for practical
applications than pure metals
12. Iron Based Superconductors
Iron-based superconductors contain
layers of iron and a pnictide such as
arsenic or phosphorus .This is
currently the family with the second
highest critical temperature, behind
the cuprates.
The crystalline material, known
chemically as LaOFeAs, stacks iron
and arsenic layers, where the
electrons flow, between planes
of lanthanum and oxygen.
Crystal structure of LaFeAsO, one of
the ferropnictide compounds
13. Cuprates
Cuprate superconductors are
generally considered to be two-dimensional
materials with their
superconducting properties
determined by electrons moving
within weakly coupled copper-oxide
(CuO2) layers. Neighboring layers
containing ions such
as lanthanum, barium, strontium, or
other atoms act to stabilize the
structure and dope electrons or holes
onto the copper-oxide layers.
Cuprates Superconducting materials.
HgBa2Ca2Cu3Ox (critical temperature to 133 K)
Bi2Sr2Ca2Cu3O10(BSCCO) (critical temperature to 110 K)
YBa2Cu3O7 (YBCO) (critical temperature to 92 K.)
14. Organic Superconductors
Superconductivity in low dimensional organic materials was first suggested by
Little in 1965.
C60 by itself is a very poor conductor. By doping this compound with electron
donors such as alkaline metals, which provide the conduction electrons,
superconductivity can be induced. K3C60 has a Tc of 19 K
Other superconductors in which conductivity arises in
the pi-electrons of unsaturated bonds have also been
discovered.
Scientists have created the first organic
superconductor based on a simple aromatic molecule,
picene (C22H14), doped with an alkali metal.Depending
on the potassium content, the materials Tc varies from
7 to 18K.
17. Power Cables
Superconducting wires carry up to five times the
current carried by copper wires with the same
cross section.
Superconducting cables are cooled to remove
the resistance to the flow of electricity, cutting
down on the losses that typically occur during
transmission.
Communications
HTS filters will enhance signal-to noise
ratios in cellular communications systems
leading to reliable communication services
with fewer spaced cell towers.
18. Limitations
For presently known practical superconductors, the temperature is much
below 77 Kelvin, the temperature of liquid nitrogen. Keeping them below
that temperature involves a lot of expensive cryogenic technology.
Scientists are working on designing superconductors that can operate at
room temperature.
Type II superconductors in particular are extremely brittle, limiting their
range of practical applications. Although Type I superconductors generally
are not as brittle.
The other major limitation of superconductors is their sensitivity to
changing magnetic fields, meaning that AC current will not work effectively
with superconductors.
