Effect of high oxygen deficiency in nano-confined bismuth sesquioxide

Simone Sanna,Vincenzo Esposito,Elisabetta Maria Firodaliso,Ivano E Castelli,Takeshi Kasama

doi:10.1088/2515-7655/ab783a

Abstract

Bismuth sesquioxide in its cubic form, i.e. δ-Bi2O3, is the fastest oxygen ionic conductor known which has important applications in energy technologies. However, the material is unstable as it undergoes high-density polymorphic transitions and degradation. In this work, we show that δ-Bi2O3 can be stabilized both at high and low temperatures (T < 775 °C) under low oxygen partial pressure (pO2 < 10−5 atm), where the material is nanostructured in multilayered thin film coherent heterostructures with yttrium stabilized zirconia. Density Functional Theory calculation confirms such a form of metastability, also showing that high oxygen defect concentration favors the cubic phase. Moreover, high oxygen deficiency in the nanoionics leads to an unexpected ‘two-regime’ conductivity with high values (σ > 1 S cm−1 at 600 °C) at high pO2 and lower ionic conductivity (σ ∼ 0.1 S cm−1 at 600 °C) at low pO2. Ionic conductivity at low pO2 occurs with high activation energy (Ea > 1.5 eV), suggesting a drastic decrease in mobility for high concentration of defects.

Highlights

Introduction pte KeywordsBi2O3, YSZ, Heterostructure, thin films, nanoionicsAmong the different strategies of tuning, “nanostructuring” is probably the most promising one
Among the fast oxygen ionic conductors, bismuth sesquioxide in its cubic form, i.e. -Bi2O3, is the ce Defective metal oxides (MeOx) that can transport oxygen at high and intermediate temperatures are the corecomponents of key energy technologies such as fuel cells, electrolysers and sensors.[1,2]
Such an attainment relies on the high tunability of the defective chemistry of MeOx that can bring to the material wide range of properties either as the result of combination of functions or even by the arising of new properties that do not belong to constitutive components.[6]

Summary

Introduction

Introduction pte KeywordsBi2O3, YSZ, Heterostructure, thin films, nanoionicsAmong the different strategies of tuning, “nanostructuring” is probably the most promising one. We have shown that nanostructuring of bismth oxide (both doped and undoped) in multilayered heterostrutures with other stable materials can lead to cubic stabilization at low pO2 and unexpected electrical properties.[13,16] Nanostructuring can stabilize the bismuth oxide component beyond its thermodynamical stability, e.g. in highly reducing conditions (H2) and at high temperatures.[13]

Results

Conclusion