Electrical properties & structure properties of iron doped ybco-247 via first principle theory / Muhammad Ashraff Hamdan

YBCO is one of the high temperature superconductors that are widely
studied by the researchers to enhance its superconducting properties. By
improving the critical temperature (Tc) and critical current density (Jc) of
the superconductor, it can be used in various applications to withstand the
high temperature. Y-123 phase is one of the YBCO family that is commonly
used to study the doping effect to the structure. The Y-123 phase has critical
temperature about 90 K. Other phase such as Y-247 is not commonly
studied due to high oxygen pressure requirements to build it. Common
studies use solid-state method or sol-gel method to make the pure and doped
YBCO. Computational method was used to study the electrical and
structural properties of Y-247. The structure was doped with different
amount of Feat Y-site and Cu-site. Using the first principle theory it can
calculate the band structure, density of states and analyze the electron
distribution. For both Y-site and Cu-site, same pattern of band structure
were shown. The valence band and conduction band are overlapped with
each other and showing the conducting properties. Copper 3d orbital state
and oxygen 2p state plays important role to maintain the superconducting
properties with electron-hole migration concept. Energy band gap at Y-site
increasing in number but decrease when x=0.08 and x=0.10 were doped to
the structure. For Cu-site, the energy band gap decrease as the concentration
of Fe increase. The Partial Density of States shown that the optimum
concentration of Fe at V-site is x=0.02 and at Cu-site is x=0.08. The
electron distribution shows a high concentration can be found in the CuO
chain and CU02 planes. The bond length among CuO chain and CU02 plane
at Cu-site decreases as the Fe concentrations increases.