Alteration of the doping state induced by thallium loss in Tl-2201

Influence of thallium content in Tl-2201 on superconductivity is investigated by annealing at different temperatures at 0.2 oxygen pressure. Deeply overdoped, non-superconducting Tl-2201s undergo a transition from non-superconducting to superconducting and then to non-superconducting state with increasing annealing temperature. By analysis of mass loss of Tl-2201 at high temperature, effects of thallium and oxygen content on superconductivity were separated. The loss of thallium results in that the Tl-2201 undergoes an alteration from over-doping to under-doping state. During annealing at temperatures lower than 500 °C, the thallium lose is ignored. The mainly feature of Tl-2201 exhibits absorption of oxygen and an increase in the mass of Tl-2201. At temperatures higher than 500 °C, the loss of thallium in Tl-2201 becomes dominant, meantime accompanying with a release of oxygen. A phase diagraph with respect to the relationship between the hole carrier concentration, the interstitial oxygen and the substitution Cu2+ for Tl3+ was discussed. The under-doped Tl-2201s only appear at low substitution Cu2+ for Tl3+ region.