Chemistry and high Tc superconductivity in the La-Ba-Cu-O system

A systematic investigation of the chemistry and superconductivity in the La-Ba-Cu-O system was carried out, using X-ray powder diffraction, resistivity and TGA measurements. A phase diagram for the La-Ba-Cu-O quasi-ternary system at 950 C has been determined and the relationship between the phases in this system is discussed. A series of A-cation (ABO3-type perovskite) deficient compounds of the type of (LaBa2)xCu3O7.0 (0.67 less than x less than 0.96) were prepared. Cation deficiencies appear to stabilize the structure but depress Tc. Partial substitution of La and Ba in LaBa2CuO7 + delta by other rare earth and alkali earth cations, respectively, were also investigated. An enhancement in Tc, compared with La1+xBa2-xCu3O7 + delta was found in LaBa2-xCaxCu3O7 + delta (0 less than x less than 1.0), providing further evidence for the importance of reduced lattice dimensions in stabilizing the superconducting phase of La-123.