Structure and charge transfer driven by the controlled amount of additional oxygen in cation-stoichiometric Bi2Sr2CuO6+δ

Polycrystalline Bi-2201 with stoichiometric cationic ratios has been prepared, and an extensive study for the determination and control of the oxygen content was carried out. The extra-oxygen amount per formula unit, δ inBi 2 Sr 2 CuO 6 + δ , ranged from 0.18 down to 0.10 under appropriate annealing conditions. The evolution of the lattice parameters with the oxygen concentration, featuring a switch in the modulation wave-vector components, is presented. In this range of compositions, T c varies from 3 K (overdoped) to 10 K (underdoped) through a maximum at 16.5 K, showing that, by fine tuning the oxygen excess, most doping levels are accessible in the nominal, substitution-free, Bi-2201.