Correlation between phase structure and electrical conduction in BISNVOX system for intermediate temperature solid oxide fuel cells (IT-SOFC)

Abstract

Samples of Sn⁴⁺-substituted bismuth vanadate, formulated as Bi₄Sn _x V_{2− x} O_{11−( x /2)− δ} in the composition range 0.07 ≤ x ≤ 0.30, were prepared by standard solid-state reactions. Sample characterization and the principal phase transitions (α ↔ β, β ↔ γ and γ′ ↔ γ) were investigated by FT-IR spectroscopy, X-ray powder diffraction, differential thermal analysis (DTA) and AC impedance spectroscopy. For composition x = 0.07, the α ↔ β and β ↔ γ phase transitions were observed at temperatures of 451 and 536°C, respectively. DTA thermograms and Arrhenius plots of conductivities revealed the γ′ ↔ γ phase transition at 411 and 423°C for x = 0.20 and 0.30, respectively. AC impedance plots showed that conductivity is mainly due to the grain contribution, which is evident in the enhanced short-range diffusion of oxide ion vacancy in the grains with increasing temperature. The highest ionic conductivity (5.03 × 10⁻⁵ S cm⁻¹ at 300°C) was observed for the x = 0.17 solid solution with less pronounced thermal hysteresis.

Keywords:

• BIMEVOX
• phase transition
• AC impedance
• ionic conductivity

Acknowledgements

The authors thank the Chairman, Department of Chemistry, Aligarh Muslim University for providing necessary research facilities and the Vice-Rector of higher studies and scientific research of Taiz University for his kind support.