2. Introduction
Father of Super conductivity is H.Kamerlingh Onnes’
Duch Physicist (1911).
In his experiments on the properties of metals in general
and on the electrical conductivity of Mercury (Hg):
He observed that, when pure mercury is cooled, its
resistivity vanished abruptly at 4.2 K. Above this temperature,
the resistivity is immensurable, while below this temperature
the resistivity is very small that it is essentially zero. ( is in
the order of 105 ohm cm).i.e., at 4.2 K, Hg is converted into a
superconductor.
This phenomenon of loosing resistivity absolutely when
cooled to a sufficiently, low temperature is called `super
conductivity’.
3. SUPERCONDUCTORS:
Superconductors are the materials that have almost
zero resistivity and behave as diamagnetic below the
superconducting transiting temperature.
Superconductivity is the flow of electric current without
resistance in certain metals, alloys, and ceramics at
temperatures near absolute zero, and in some cases at
temperatures hundreds of degrees above absolute
zero.
4. TransitionTemperature (or) Critical
Temperature
The temperature at which the transition of a normal
conductor into a superconductor occurs is called as the
`Transition temperature or critical temperature [Tc].
Above Tc- the substance is in the normal state, but
Below Tc-The substance is in the super conducting state.
For semiconductors -Tc varies from, 0.3K to 1.25K
For metals -Tc varies from 0.35K to 9.22K and
For alloys -Tc varies from 18.1K to 22.65K.
5. High-temperature superconductors
(abbreviated high Tc) are a family
of superconducting materials
containing copper-oxide planes as
a common structural feature. For
this reason, the term is often used
interchangeably with cuprate
superconductors.
High Temperature Superconductors (HTS)
Resistance of mercury vs temperature
6. This feature allows some materials to support
superconductivity at temperatures above the boiling point
of liquid nitrogen (77 K). Indeed, they offer the highest
transition temperatures of all superconductors. The ability
to use relatively inexpensive and easily handled liquid
nitrogen as a coolant has increased the range of practical
applications of superconductivity.
Notations Chemical formula Tc (K)
1 2 3 YBa2 Cu3 O7 90
Tl-1212 Tl Ba2 CaCu2 O7 80
Some examples of HTS:
7. Characteristics of HTSC
Superconductors are characterized by a material-
dependent magnetic field H, above which the
superconducting state disappears.
The critical field is a function of temperature. All the HTS
materials are type II superconductors. When the applied field
H < Hc1, the material is in the superconducting Meissner
state whereas in the mixed state, the magnetic field
penetrates partly into the material in the form of vortices.
Type II superconducting materials have usually higher
critical fields than type I superconductors which makes them
suitable for many advanced applications.
8. Critical magnetic field as a function of
temperature for (a) type I superconductors and
(b) type II superconductors.
Most of the HTS materials are
layered cuprates, i.e., they consist
of CuO2 planes separated by
layers of other elements or oxides.
Because of the layered structure,
HTS materials exhibit strong
anisotropy: the values of the
superconducting parameters are
different in different directions. In
addition, charge transport is mainly
confined to the CuO2 planes.
9. IMPORTANT FEATURES HTS
They have high Tc.
They have PEROVSKITE crystal structure.
They are direction dependent
They are reactive, brittle and cannot be easily formed (or)
joined.
HTS Material - YBCO
HTS materials usually have complicated crystal
structures.
The compounds of HTS almost consists more than three
different chemical elements and the materials with the highest
Tc have seven elements in the crystal lattice.
Ex: YBa2Cu3O7-d (YBCO). YBCO has numerous
advantages compared to other ceramic superconductors
10. APPLICATIONS OF SUPERCONDUCTORS
1. Superconducting Transmission Lines
Since 10% to 15% of generated electricity is
dissipated in resistive losses in transmission lines, the
prospect of zero loss superconducting transmission lines
is appealing.
Current experiments with power applications of high-
temperature superconductors focus on uses of BSCCO in
tape forms and YBCO in thin film forms. Current densities
above 10,000 amperes per square centimeter are
considered necessary for practical power applications,
and this threshold has been exceeded in several
configurations.
11. 2. Superconducting Motors and Generators
Superconducting motors and generators could be
made with a weight of about one tenth that of conventional
devices for the same output. This is the appeal of making
such devices for specialized applications. Motors and
generators are already very efficient, so there is not the
power savings associated with superconducting magnets. It
may be possible to build very large capacity generators for
power plants where structural strength considerations place
limits on conventional generators.
3. Superconducting Magnetic Energy Storage
Superconducting magnetic energy storage (SMES)
stores electricity for long periods of time in superconductive
coils. SMES will be used by electrical utilities some day.
12. 4. Superconductors in NMR Imaging
Superconducting magnets find application in magnetic
resonance imaging (MRI) of the human body. Besides
requiring strong magnetic fields on the order of a Tesla,
magnetic resonance imaging requires extremely uniform
fields across the subject and extreme stability over time.
Maintaining the magnet coils in the superconducting state
helps to achieve parts-per-million special uniformity over a
space large enough to hold a person, and ppm/hour stability
with time.
13. 5. Fault-Current Limiters
High fault-currents caused by lightning strikes are a
troublesome and expensive nuisance in electric power grids.
One of the near-term applications for high temperature
superconductors may be the construction of fault-current
limiters which operate at 77K. The need is to reduce the fault
current to a fraction of its peak value in less than a cycle (1/60
sec).
6. Magnetically Levitated Trains
Perhaps the most famous and fascinating
superconducting invention is magnetically levitated trains, or
"maglev" trains. Maglev trains have no wheels and friction.
The trains float silently on a magnetic field due to diamagnetic
behavior.
14. TO OUR KIND SIR RAFIQUE AND
OUR CLASS FELLOWS TO HEARING OUR
PRESENTATION CAREFULLY.
THANKS
