Electrical Properties and Microstructural Analysis of Aliovalent-Ion (Y³⁺, Nb⁵⁺)–Doped Bismuth-Based Solid-Oxide Electrolyte

Abstract

Bi_1−x Nb _x O_1.5+δ (x = 0.15–0.25) and Bi_1-y Y _y O_1.5 (y = 0.2–0.3) electrolytes were synthesized using solid-state reaction. The electrolytes have a δ-Bi₂O₃ structure and are stable at room temperature. A Bi_0.8Y_0.2O_1.5 sample that was sintered at 950°C showed the highest conductivity of ∼1.97 S/cm at 800°C, while that of Bi_0.85Nb_0.15O_{1.5 +  δ} sintered at 950°C is 0.41 S/cm. The grain sizes of the Bi_0.85Nb_0.15O_{1.5+ δ} and Bi_0.8Y_0.2O_1.5 samples sintered at 950°C are ∼29.4 and 10.6 μm, respectively. The thermal expansion coefficients of the Bi_0.85Nb_0.15O_{1.5+ δ} sample are 12.1 × 10⁻⁶/°C at 30–500°C and 22.3 × 10⁻⁶/°C at 500–800°C, while those of the Bi_0.8Y_0.2O_1.5 sample are 15.4 × 10⁻⁶/°C at 30–500°C and 20.3 × 10⁻⁶/°C at 500–800°C.

Keywords:

• Solid-oxide fuel cell
• solid electrolyte
• bismuth oxide
• defect-fluorite structure

Acknowledgments

We thank the National Science Council of Taiwan for funding support through contracts NSC 100–2221-E-027–109 and NSC 101-2221-E-027-021.