Long-Term Conductivity Stability of Metastable Tetragonal Phases in 1Yb₂O₃–xSc₂O₃–(99 – x)ZrO₂ (x = 7, 8 mol %)

Abstract

The present work studies the influence of 1 mol % Yb 2 O 3 codoping on the long-term conductivity stability in the metastable tetragonal phases present in 8−9 mol % Sc 2 O 3 −ZrO 2 . Dense polycrystalline samples are synthesized via conventional solid-state reaction and pressureless sintering methods. The 8 mol % dopant containing ZrO 2 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 1Yb 2 O 3 −8Sc 2 O 3 −91ZrO 2 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 % Yb 2 O 3 (for Sc 2 O 3 ) is beneficial in reducing the % conductivity degradation from 16 to 10% in 8Sc 2 O 3 − 92ZrO 2 , it does not affect the long-term conductivity stability in 9Sc 2 O 3 −91ZrO 2 (∼3%). Thus, the 9Sc 2 O 3 −91ZrO 2 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.

Long-Term Conductivity Stability of Electrolytic Membranes of Scandia Stabilized Zirconia Co-Doped with Ytterbia

“…The maximum conductivity degradation (10–16%) after 2000 h of aging was observed for compositions with a total concentration of stabilizing oxides equal to 8 mol%. Compositions containing 9 mol% of stabilizing oxides were relatively stable (conductivity degradation was 3%) [ 30 ]. Aging of (ZrO 2 ) 0.90 (Sc 2 O 3 ) 0.09 (Yb 2 O 3 ) 0.01 samples at 900 °C for 500 h led to a decrease in conductivity by 20% [ 31 ].…”

Phase Stability and Transport Properties of (ZrO2)0.91−x(Sc2O3)0.09(Yb2O3)x Crystals (x = 0–0.01)

“…Currently, there is interest in studying the structure and transport characteristics of ceramic and crystalline samples of ZrO 2 -Sc 2 O 3 solid solutions additionally doped with Yb 2 O 3 [24][25][26]. The effect of long-term annealing at 650 • C in air on the properties of ZrO 2 solid solutions containing 8-9 mol% Sc 2 O 3 and additionally co-doped with 1 mol% Yb 2 O 3 has been studied [27]. It was shown that the introduction of 1 mol% Yb 2 O 3 reduces the degradation of the conductivity of ZrO 2 -Sc 2 O 3 solid solutions.…”

Role of Divalent Co-Dopant as Structure Stabilizer in Scandia-Stabilized Zirconia Electrolyte for SOFC

“…In this order, Y 3+ (104 pm) Yb 3+ (100.8 pm), and Ce 4+ (101 pm) were mostly used as binary co-dopants. [19][20][21][22] Among these, 1 mol% ceria co-doped in 10 mol% scandia stabilized zirconia (1Ce10SSZ) became the popular choice of market leaders due to its remarkable conductivity (∼0.15 S cm −1 at 850 °C) along with minimum aging rate (∼15% in 4000 h at 850 °C) in air. 23 Furthermore, Omar et al 24 observe this aging behavior of 1Ce10SSZ in the air as well as reducing atmosphere at 600 °C.…”

“…26 Apart from Ce 4+ , other co-dopants such as Y 3+ and Yb 3+ were also added in SSZ to suppress its aging behavior. 19,24,27 Politova and Irvine 27 examine the effect of systematic substitution of Sc 2 O 3 with Y 2 O 3 in 11SSZ. They found out that the presence of yttria in 11SSZ stabilized the cubic structure but reduced the conductivity as well.…”