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++M2+II) for 2 La3+ (MII=Ba, Pb) or (M6+VI+3M2+II) for 4 La3+ (MVI=Mo, W; MII=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.