CO(III)–NI(II) double substituted bismuth vanadate: synthesis, phase stabilization, and structural and electrical characterization

Abstract

Samples of Co–Ni double substituted bismuth vanadate, BICO0.20−xNIxVOX (Bi4Co0.20 − x(III)Nix(II)V1.8O10.8 − (x/2) − δ;0 ≤ x ≤ 0.20) were synthesized by standard solid state reactions. The influence of Ni substitution for Co on phase stabilization and oxide-ion performance have been investigated using X-ray powder diffraction, differential thermal analysis, and AC impedance spectroscopy. The high conducting γ′-phase was effectively stabilized at room temperature for compositions with x ≥ 0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380 °C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (∼2.56 × 10−4 S cm−1 at 300 °C) was observed for the composition with x = 0.13. However, a good agreement was generally found between the values of electrical conductivity and corresponding activation energies of conduction.