PREPARATION AND TRANSPORT-PROPERTIES OF SINGLE-PHASE TLBA1+XLA1-XCUO5 (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5)

The preparation of polycrystalline TlBa1+xLa1-xCuO5 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) is investigated using Tl-free precursors. Single-phase samples are obtained except for x = 0.5, in which a small amount of impurity phase is detected. Compositional and structural analyses confirm good homogeneity of the Ba and La distribution in each sample. In this system, hole-carrier doping increases with increasing x. The sample with x = 0, TlBaLaCuO5, shows semiconductive resistivity (rho) and a T-independent Hall coefficient (R(H)), indicating two-dimensional (2D) variable range hopping. As x increases, the resistivity becomes metallic and superconductivity is observed for 0.1 less-than-or-equal-to x less-than-or-equal-to 0.4, with a maximum T(c) value of 45 K at x = 0.2. For x = 0.5, the sample is metallic but not superconducting. In all metallic samples (0.1 less-than-or-equal-to x less-than-or-equal-to 0.5), R(H) has a broad maximum at about 100 K, as seen in most high-T(c) cuprates. The inverse Hall mobility, mu(H)-1 = rho/R(H), roughly obeys a T2 dependence regardless of the T(c) value, which is widely observed in other oxide superconductors.