Study of Structure and Electrical Transport Property in Composite and Doped Systems of YBa2Cu3O7-δ Superconductor

Abstract

A dramatic change in the research activity has taken place when high temperature superconductors (HTSCs) having Tc of 90 K, above the boiling point of liquid nitrogen (77 K), was established in YBa2Cu3O7-δ (YBCO). We have selected the well-studied material, YBCO, as
our parent material, for its relatively less anisotropic and less toxic nature with easily reproducible phase over other cuprates. HTSCs are widely used in various fields including medical diagnosis like Magnetic Resonance Imaging (MRI), Superconducting Quantum Interference Devices (SQUIDs), Transistors, Josephson Junction Devices, Circuitry connections, Particle accelerators, Sensors, Energy Storage etc. The in-homogeneities such as mesoscopic in-homogeneities (grain boundaries, voids, and
cracks), secondary phases and microscopic in homogeneities such as oxygen deficiencies, chemical in-homogeneities, and local strains are induced in the HTSC systems during their preparation. Hence, HTSCs are defect ridden. Properties of HTSC are modified by doping and
making composites of ferroelectric, dielectric and magnetic materials. Composites of YBCO with other materials started flourishing to enhance material property such as critical temperature Tc, critical current density Jc, transition width ΔTc , normal state resistivity etc. Substitution at the Cu site is most important among all the cations of YBCO, as Cu-O networks play a major role for the occurrence of superconductivity in these materials. Ion irradiation can also improve the material’s property by the addition of defects. The controlled defects produced by the collision cascade
obtained by fast moving neutrons, point defects created by low energy ion impact and columnar defects generated by swift heavy ions result in significant enhancement of critical current density. Because of the huge energy loss, the ions in a medium can bring several changes in the target system such as annealing of defects, additional defects, resistivity enhancement, phase change. Ion irradiation can also modify the local geometrical arrangements through introduction of
defects which induces resistivity changes in HTSC. Studies on ion beam irradiation of thin films
of YBCO showed that Tc can be controllably reduced.
In the present thesis, an attempt has been made to understand the interplay between the inhomogeneities,
secondary phases and the thermal fluctuations around the superconducting transition