Bi-La-based oxide conductors with rhombohedral Bi-Sr-O type: Structural and conductivity properties optimization by polycationic substitutions for La

In Bi0.775La0.225O1.5, the best oxide conductor of the hexagonal-layered materials family known as the Bi-Sr-O type, partial polycationic substitutions for La3+, such as (Ce4+ + M-II(2+)) for 2 La3+ (M-II = Ba, Pb) or (M-VI(6+) + 3M(II)(2+)) for 4 La3+ (M-VI = Mo, W; M-II = Ba, Pb), have been realized; these substitutions have induced an enlargement of the cationic slab thickness and thus allowed improvement of the conductivity, The resulting modifications of a and c lattice constants have been interpreted on the basis of the characteristics of the substituting elements (cationic radii and symmetries) and were correlated to the observed conductivity modifications. (C) 2000 Academic Press.