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 ma terials family known as the Bi-Sr-O type, partial polycationic substitution s 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 realiz ed; these substitutions have induced an enlargement of the cationic slab th ickness and thus allowed improvement of the conductivity, The resulting mod ifications of a and c lattice constants have been interpreted on the basis of the characteristics of the substituting elements (cationic radii and sym metries) and were correlated to the observed conductivity modifications. (C ) 2000 Academic Press.