SOLID-PHASE SYNTHESIS AND CHARACTERIZATION OF NEW BIMEVOX SERIES - BI(4)V(2-X)M(X)O(11-X) (M=CR-III, FE-III)

Two new BIMEVOX series Bi(4)V(2-x)M(x)O(11-x) (M = Cr-III, Fe-III) hav e been investigated by X-ray powder diffraction, thermal analysis and ionic conductivity measurements. Structural phase transitions alpha <- ---> beta and beta <----> gamma occur as a function of composition and temperature in iron substituted phases for which a new orthorhombic d omain is evidenced when x exceeds 0.5. At low temperature, the Cr comp ounds retain the alpha orthorhombic symmetry where an incommensurate s tructural modulation is observed. The structure of the tetragonal phas e Bi4V1.5Fe0.5O10.5 has been refined by the Rietveld method. The anion ic properties are compared to those of other iso- or aliovalent cation substituted BIMEVOX and discussed in terms of electronic configuratio n and site preference of the doping cation.