Effects of silver-doped on barium-site of ybc0123 superconductor using density functional theory via first principle study / Fatin Nadiah Abdul Jabar

The effect of Ag-doping on Ba-site of YBCO phase 123 has been analysed via
computational simulation to determine the structural and electronic properties. The
software used in this project is Material Studio, CASTEP. The structural properties
that have been analysed were lattice parameter and bond length while the electronic
properties were band structure, density of state, partial density of state and electron
density difference. Generally, YBCO has a perovskite-orthorhombic structure where
a ≠ b ≠ c. The orthorhombicity in this project remains unchanged as there were not
much difference in lattice parameter for all concentrations of dopant. The bond
length at concentration x=0.2500 shows a structural modification due to the changes
in oxygen content at CuO chain and changes in electronic arrangement in CuO plane.
From the simulation of Material Studio CASTEP software through Density
Functional Theory, the optimized crystal structure has been developed. The band
structure at the concentration x=0.2500 shows no energy band gaps since the
conduction bands and valence bands overlap with each other. The density of states
graph shows that the electron near and above Fenni level was highly concentrated
which are involved in the formation of superconducting properties. Based on other
studies and theory, we can assume that when the YBCO is over-doped which is more
than x=0.2500, it will destroy the superconductivity properties. This is resulting in
the excess of hole content which will lower the critical current density, Jc and critical
temperature, Tc.