germanium.
Muller gave the idea of high temperature superconductivity in a new class of
ceramic materials. They found evidence for superconductivity around 40 K in
ceramic and the results were unambiguously confirmed and era of high
temperature superconductivity (HTSC) was ushered in. In the beginning of 1987,
rare earth metal oxides were synthesized with a TC of
93 K. Thus, for the first time, there was existence of superconductor with a TC above that of liquid nitrogen (boiling point
77 K). Liquid nitrogen cryogenic systems are less complex, less expensive than
the system using helium refrigeration. Nitrogen cooling can be used for the
development of microelectronic technology (semiconductor superconductor
devices).
The maximum value of TC has now increased to 133 K for mercury based
cuprate HgBa2Ca2Cu3O8. When this compound is subjected to high pressure ~ 30GPa, the
value of TC increases to 164 K. While
HgBa2Ca2Cu3O8 cannot be needed in
applications of superconductivity at such high pressures. This result suggests
that the value of TC near to 160 K or even
higher are attainable at atmospheric pressure.
Q.11 Discuss the characteristics of superconductor
in superconducting states.
Related
Questions -
Q. Disscuss the characteristic properties
of super conductor. (AKTU. 2009-10)
Ans. Characteristics of Superconductors In
Superconducting States: -
We shall study the characteristics under
the following two aspects:
1. Characteristics
which do not change in superconducting transition.
2. Characteristics
which change in superconducting transition.
Characteristics
Which Do Not Change In Superconducting Transition: -
1. There
is no change in crystal structure as revealed by X-ray diffraction studies.
This suggests that superconductivity is more connected with the conduction
electrons than with atoms themselves.
2. The
photoelectric properties are unchanged, i.e., no change in absorption of fast
or slow electrons.
3. The
thermal expansion and elastic properties do not change in transition.
4. In
absence of magnetic field, there is no change of latent heat and no change of
volume in transition.
Characteristics
Which Change In Superconducting Transition: -
1. At
transition, all magnetic flux is ejected out by the superconductor and it
behaves as a perfect diamagnetic substance.
2. Superconducting
state is destroyed by applying a field equal to the critical field HC on the specimen.
3. The
specific heat does not very as the absolute temperature in superconducting
state but it is found to vary exponentially with temperature.
