Local Structure and Conductivity in the BIGAVOX System

While BIMEVOX systems have attracted attention for their fast oxide-ion conductivity at intermediate temperatures, there are only a limited number of reports concerning local structure. In this work, both long-range and structures in the Bi2V1–xGaxO5.5–x–δ (BIGAVOX, 0.025 ≤ x 0.40) system investigated using X-ray powder diffraction (XRD) combination total scattering, 51V 71Ga solid-state nuclear magnetic resonance (NMR), Raman spectroscopy, supported by electrical measurements a.c. impedance spectroscopy. The three main polymorphs, α, β, γ, observed room temperature over compositional ranges < 0.10, 0.10 0.20, 0.20 0.40, respectively. Above = as more Ga is introduced into lattice, general growth distance between bismuthate vanadate layers observed, indicating increasing ionicity interaction these layers. found to adopt octahedral tetrahedral geometries, while V polyhedra include tetrahedral, pentacoordinate, geometries. With x-value, vacancy concentration increases, transform lower coordinate resulting decrease average V–O bond length. Reversible α ↔ β γ phase transitions on heating 0.05 composition, γ′ 0.15 compositions, γ-BIGAVOX compositions (x 0.25) generally show high ∼10–2 S cm–1 600 °C.