Hole concentration and critical temperature in TI_2-y,Ba_2-zLa_zCuO_6-x

Samples of the system TI_2-y,Ba_2-zLa_zCuO_6-x with starting values of y=0.00 and 0.35 for 0≤z≤0.2 have been synthesized at 860-880 °C in sealed gold tubes and then quenched in liquid N₂. The lattice parameters and critical temperature T_c, were measured, and chemical analysis was made for y and x of the single-phase products before a further anneal at 350°C in 1 atm O₂. During the 0, anneal, samples with a starting value of y=0.00 extruded thallium to form TI₂O₃ and transformed from tetragonal to orthorhombic; samples with a starting value of y=0.35 did not. The data indicate that the superconductive samples are p-type at the high oxidation side of the range of superconductor solid solutions and that all samples contain TI 6s electrons. Without a quantitative knowledge of the concentration of TI 6s electrons, it was not possible to obtain a quantitative plot of T_c versus the hole concentration, p, per Cu atom in the CuO₂ sheets, but for Δp=0.10, ΔT_c= -52 °C, showing that T_c drops sharply with increasing p. We also conclude that TI extrusion to form TI₂O₃ proceeds by an ordered removal of TI until the Fermi energy E_f falls below a mobility edge in the TI 6s band.