Long-Term Conductivity Stability of Metastable Tetragonal Phases in 1Yb₂O₃–xSc₂O₃–(99 – x)ZrO₂ (x = 7, 8 mol %)
2020
Shukla, Vandana | Singh, Shashwat | Subramaniam, Anandh | Omar, Shobit
The present work studies the influence of 1 mol % Yb₂O₃ codoping on the long-term conductivity stability in the metastable tetragonal phases present in 8–9 mol % Sc₂O₃–ZrO₂. Dense polycrystalline samples are synthesized via conventional solid-state reaction and pressureless sintering methods. The 8 mol % dopant containing ZrO₂ compositions contain the metastable t′-phase, while the t″-phase exists in the 9 mol % doped compositions. However, the grain conductivity values in all of the compositions are comparable and insensitive to the type of tetragonal phase present in the samples. The total conductivity follows a similar trend except in the 1Yb₂O₃–8Sc₂O₃–91ZrO₂ specimen, which shows a low total conductivity because of the resistive grain boundaries. Long-term thermal aging is performed on all of the tested samples at 650 °C for 2000 h in air. The in situ conductivity study suggests that the conductivity declines occur primarily in the first 650 h. The total conductivity loss at 650 °C is higher in the t′-phase (∼10–16%) compared to the t″-phase (∼3%). Even though substituting 1 mol % Yb₂O₃ (for Sc₂O₃) is beneficial in reducing the % conductivity degradation from 16 to 10% in 8Sc₂O₃–92ZrO₂, it does not affect the long-term conductivity stability in 9Sc₂O₃–91ZrO₂ (∼3%). Thus, the 9Sc₂O₃–91ZrO₂ composition exhibits excellent temporal stability of oxygen-ion conductivity with the magnitude of 20.4 mS·cm–¹ after 2000 h aging at 650 °C in air.
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