Superconducting magnets have a variety of industrial, medical
and research applications. This review discusses the prospects for
MgB2
superconductor for practical magnet applications vis-à-vis the intermetallic low
(LTS) and high temperature superconductor (HTS) cuprates. It has high
TC (39 K),
high JC
(105–106 A cm−2 at 4.2 K and in
the self-field) and HC2
(15–20 T at 4.2 K) in wire/tape geometry, with great scope for further improvement in the coming
years, making it a promising candidate for practical applications. The superconducting properties of
MgB2
differ from those of LTS and HTS in many ways. Besides the unusually high
TC, MgB2 has a
large coherence length, low anisotropy and transparent grain boundaries. The most important difference
between MgB2
and other practical superconductors is that it has two superconducting gaps originating
from two different bands. Tuning the scattering rates between the two bands
improves the superconducting properties and the practical applicability of
MgB2. The different methods
of fabrication of MgB2
conductors are described and compared. Fabrication of long length
MgB2
conductors is relatively easy and less expensive as compared to HTS and the
method allows the use of a variety of sheath materials with suitable barriers or
reinforcement. The conductors have much better mechanical properties for practical
applications. The critical issues and the challenges to be addressed for realization of
MgB2
superconductors as the first choice for high field magnet applications are discussed. At present
MgB2
is most suited for 20–25 K operation in fields of 1–2 T.
The discovery of superconductivity at relatively higher temperatures in a non-cuprate system, LnFeAsO 1−x F x (Ln = lanthanides) has created tremendous activity among the reseachers in this field. This review is an overview on the present status and the future scope for iron pnictides. The various structural categories of iron based superconductors, the structural aspects, different preparation techniques of the material and the necessity for its optimization are discussed. The highlighting features of iron pnictide, i.e. the very high upper critical field, moderate magneto-transport and thermal properties, are also included. The article gives a summary of the prevailing arguments of researchers to relate the material to cuprates and also the comparative features of classical and MgB 2 superconductors. The existing challenges, such as optimizing synthesis methods for technological applications and clarifying the ambiguity in the superconducting mechanism and the flexibility of the material for any site substitution, will keep iron based superconductors on the frontiers of research for a long time, in parallel to HTS.
The effects of Gd addition on the phase evolution and superconducting properties of
(Bi, Pb)-2212 prepared in the bulk polycrystalline form were studied. The Gd
content in the samples was varied from 0.0 to 0.5 on a general stoichiometry of
Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1GdxOy. Phase analysis by means of x-ray diffraction, microstructural examination by scanning electron
microscopy and superconducting property studies were carried out to evaluate the relative
performances of the samples. It is observed that Gd addition enhances the transition temperature
(TC) and critical
current density (JC)
of the system. Moreover no secondary phase containing Gd ions or any other cations was
observed after the final stage of heat treatment. Microstructural examination shows
clear and distinct morphologies for the Gd-added samples, wherein the grain
growth is suppressed by the addition of Gd and the edges of the grains become
more and more rounded. As a result, there is an increase in the porosity of the
Gd-added samples, leading to a reduction in the sintered density for these samples.
The critical current density and flux pinning properties of
Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1Oy
(where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) prepared by solid state synthesis in bulk polycrystalline
form were studied. The samples were characterized by powder x-ray diffraction
(XRD), scanning electron microscopy (SEM) equipped with energy-dispersive x-ray
analysis (EDS) and superconductivity measurements. The critical temperature
(TC), critical current
density (JC) and field
dependence of JC
of the Eu-substituted samples were found to be highly enhanced for optimum
doping levels. The peak position of the normalized pinning force density
(Fp/Fpmax) is found to shift to higher fields (0.88 T) for optimally doped samples
in contrast to 0.2 T for the undoped sample. The enhancement of the
JC–B characteristic and
pinning force density FP
(FP = JC × B) due to Eu substitution is of great technological significance.
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