High oxide ion conductivity in the Bi3+ doped melilite LaSrGa3O7

Highlights: • Bi-doped LaSrGa₃O₇ materials were synthesized by a solid state reaction method. • The Bi³⁺ replacing for Sr²⁺ would introduce interstitial defects into the structure. • The substitution of Bi³⁺ for Sr²⁺ significantly enhanced the oxide ion conductivity. A series of LaSr_1-xBi_xGa₃O_7+0.5x (0 ≤ x ≤ 0.4) materials have been synthesized by a traditional solid state reaction method. The Bi³⁺ ions enter the lattice of LaSrGa₃O₇ and occupy the La/Sr sites, which is validated by Rietveld refinement and Energy Dispersion Spectrum (EDS) analysis, introducing interstitial oxide ions into the structure. The formation energy of this interstitial defect calculated by density functional theory (DFT) is ∼2.21 eV, consistent with the high solid solubility of Bi³⁺ in LaSrGa₃O₇ from experimental data. The substitution of Bi³⁺ ions for Sr²⁺ ions can significantly enhance the oxide ion conductivity, e.g. 1.62 × 10⁻² Scm⁻¹ at 800 °C for x = 0.4, making these materials promising for practical application in SOFCs and oxygen separation membrane.