Study on phase stability and oxide ion conductivity in the BIAGVOX system

A novel oxide ion conductor, BIAGVOX formulated as Bi4AgxV2−xO11−(2x)−δ is obtained by substituting a fraction (x) of V5+ by Ag+ in Bi4V2O11 samples of the BIAGVOX system in the composition range, 0.05≤x≤0.30 were synthesized using the standard solid-state reaction. XRPD, FT-IR, DTA and AC impedance spectroscopy were used for the investigation of the correlation between the structural phase stability and oxide ion performance of the BIAGVOX materials. It has been found that orthorhombic, β, and incommensurate tetragonal, γ′ were stabilized at room temperature for compositions with x≤0.15 and x≥0.20, respectively. The enthalpy of β→γ and γ→γ transition exhibited a general drop with increasing Ag content and a minimum transition temperature was observed for x=0.20. However, the oxide ion conductivity at lower temperatures remarkably increased in composition stability ranges of β- and γ-phase, while a maximum conductivity was reported for the high temperature γ-phase at x=0.15. However, the low temperature conductivity, σ300°c measured for x=0.30 was found to be comparable with the maximum ionic conductivity of the BICUVOX system reported for x=0.20 at the same temperature.

► Stabilization of tetragonal, γ′-BIAGVOX at room temperature.
► Compositionally dependent stability of β→γ and γ′→γ transition.
► Rapid disordering of oxide vacancies with the γ′→γ transition.
► Good oxide ion performance of BIAGVOX at lower temperatures.