Novel series of thallium cuprate superconductors

The $TlCa_{1-x} Ln_x Sr_2 Cu_2 O_{7+\delta}$(Ln = rare earth) system shows electron-superconductivity when x = 0.25 and hole-superconductivity when x > 0.25. The $T_c$ is generally in the 60–90K in both these regimes. $TlSr_{2-x} La_x CuO_y$ (1021) also show electron or hole superconductivity $(T_c\sim40K)$ depending on