STRUCTURE AND CONDUCTIVITY OF CU AND NI-SUBSTITUTED BI4V2O11 COMPOUNDS

The partially Cu- or Ni-substituted compounds (Bi4V2(1-x)M2xO11-3x; M = Cu, Ni) are highly oxygen-conducting. Three phases (alpha, beta, gam ma) are observed in the unsubstituted compound; alpha is the low-condu cting room temperature phase and gamma the high-conducting phase at hi gh temperature. Structure and conductivity are studied as a function o f the substitution on the vanadium sites. Between 0 and 6% at room tem perature, the Cu compound remains in the orthorhombic alpha phase and its ionic conductivity increases. A strong anisotropic conductivity is observed. For 0.07 less-than-or-equal-to x less-than-or-equal-to 0.12 , the average structure is tetragonal (gamma-type) at room temperature . The conductivity is very high and does not vary very much over this substitution range. Impedance spectroscopy measurements have also been carried out on the x = 0.07 Ni-substituted compound. Commensurate or incommensurate superstructures are observed for all of these compounds .