Thermal stability and impedance spectroscopy studies of (Cu, Ni) substituted Bi4V2O11 ceramics

Polycrystalline samples of the oxygen ion conductor Bi₂V_0.9Cu_0.1−xNi_xO_5.35 with various contents of nickel (0 ≤ × ≤ 0.1) were investigated. The X-ray powder diffraction revealed the tetragonal structure of all compositions. DTA curves exhibit effects due to phase transition, one endothermic effect during heating and one exothermic one during cooling. The impedance of the ceramics with Pt electrodes was measured in the frequency range 10⁻¹–10⁷ Hz at constant temperatures between 350 and 920 K. The conductivity was determined by nonlinear least-squares analysis of the impedance spectra. Separation of the total resistance into grain interior and grain boundary components was feasible at temperatures below 580 K. The transition temperatures observed in DTA coincide with those observed in conductivity measurements. A phase transition, involving a reordering process of the oxygen ions is considered to be responsible for this phenomenon. The frequency dependent part of the intragrain conductivity was modeled by a constant phase admittance. The effective hopping rate was estimated by comparing the frequency dependent part and the dc limit of the intragrain conductivity. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997.