Correlation of superconducting transition temperature and hole concentration with selective oxygen distribution in the YBa2Cu3Ox lattice

This paper reports on the evaluation of available structural and photoelectron spectroscopy data on orthorhombic YBa2Cu3Ox which indicates that a two stage correlation exists between selective oxygen occupancy of the chain sites and the superconducting transition temperature, Tc, as well as hole formation at the O-ligand sites. It appears that equal changes in the oxygen occupancy in the chains in two separate stoichiometric ranges are associated with strikingly different changes in the Tc and hole formation. As x is increased from ∼6.6 to ∼6.8, a concentration range which corresponds to a low to high Tc Transition, a preferential redistribution of oxygen occurs, from non-chain to chain sites on the basal plane, transforming a disordered orthorhombic lattice into an ordered orthorhombic structure with concomitant increase in the hole formation