A method for doping Tl-based cuprate superconductors with holes

We previously demonstrated that the Tc for a Tl-2223 superconductor was increased to above 125 K when the sample was encapsulated in an evacuated quartz tube and post-annealed at 750degC for 250 h. It was indicated by thermo-electric power measurements that the post-annealed Tl-2223 sample had a hole concentration higher than an as-sintered Tl-2223 sample. Moreover, when the same encapsulation-and-post-annealing (ECPA) technique was applied to a TL-2212 phase and a Tl-2234 sample, the Tc decreased in the case of Tl-2212 while it increased in the case of TL-2234 phase. This demonstrated that the ECPA technique was effective in increasing the hole concentration in both over-doped (i.e. Tl-2212) and under-doped (i.e. Tl-2223 and Tl-2234) phases. Judging from the changes in the lattice constants and the chemical composition, it was likely that the increases in hole concentration and the subsequent changes in Tc were due to decreases in the Tl content during ECPA processes. (orig.)