Structural Characteristics and Electrical Conductivity of Spark Plasma Sintered Ytterbia Co‐doped Scandia Stabilized Zirconia

Abstract

The effect of replacing Sc2O3 with Yb2O3 on the structural and electrical properties of xYb2O3–(12–x)Sc2O3–88ZrO2 has been investigated. Spark plasma sintering technique is employed to fabricate dense bulk samples from the nano‐sized powders. X‐ray diffraction and transmission electron microscopy performed on pellets indicate the existence of cubic and rhombohedral phases in 12ScSZ, and a single cubic phase in all the co‐doped compositions. However, Raman spectroscopic studies suggest the presence of a metastable tetragonal t″‐phase along with rhombohedral phases in 12ScSZ, whereas a single cubic phase in all the co‐doped compositions. Significant enhancement in the conductivity of grain and grain boundary is observed on replacing Sc2O3 with Yb2O3. In the intermediate temperature range, 1Yb11ScSZ exhibits the highest, while 12ScSZ shows the lowest conductivity values, which is attributed to corresponding phases present in that range. Through co‐doping with >1 mol% Yb2O3 leads to conductivity decrease, but the value remains higher than that of 12ScSZ. A sharp conductivity change is observed in 12ScSZ and 1Yb11ScSZ samples, which is attributed to partial phase transition as well to the formation of cation‐vacancy complexes. In this work, the beneficial effect of Yb2O3 co‐doping in 12ScSZ on the phase and conductivity has been highlighted.

Effect of Thermal Aging on the Phase Stability of 1Yb2O3–xSc2O3–(99 – x)ZrO2 (x = 7, 8 mol %)

“…This results in a complex assemblage of several stable and metastable phases with poorly defined phase boundaries. − It is important to comprehend these structural transformations, as this aspect plays a key role in determining the ionic conductivity in the Sc 2 O 3 –ZrO 2 system . Although the focus of numerous studies ,− has been to examine the codoping effect on the stable phases, the metastable tetragonal phases present in ScSZ have hardly received any consideration. The present work examines the influence of Yb 2 O 3 codoping on the metastable phases of t ′ and t ″ existing in ScSZ.…”

Advanced modification of scandia‐stabilized zirconia electrolytes for solid oxide fuel cells application—A review

“…As seen in Figure 4, the movement of ion oxide migrated within the solid electrolyte by a hopping mechanism through a single structure unoccupied (ie, at green arrow) and a series of oxygen vacancies (ie, at yellow arrow). 87 Several additional trivalent cations have been introduced to the ScSZ electrolyte, including ceria codoping, 84 dysprosium co-doping, 85 ytterbia co-doping, 88 magnesia co-doping, 89 and bismuth co-doping. 90 The optimum concentration of co-doping was an important parameter to be measured in order to achieve the high efficiency of the solid electrolyte.…”

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

“…The formation of the β-phase in high Sc 2 O 3 -containing compositions is shown to be caused by the long-range ordering of oxygen vacancies, which can be suppressed either by adding a slight amount of codopants or by heating the sample above 600 °C. 17,18 Although the addition of codopants stabilizes the c-phase and prevents a sudden drop in conductivity on lowering the temperature below 600 °C, the overall conductivity in this compositional range (>10 mol % Sc 2 O 3 ) is severely reduced. This conductivity decrease is related to the defect interactions, which result in the formation of local defect complexes (such as (Sc Zr / −V o •• −Sc Zr / ) × , (Sc Zr / −V o •• ) • , etc.).…”

“…Finally, the correlations between the microstructure and conductivity will be established in both the unaged and aged samples. It is important to note that our earlier reported work though focused on Yb 2 O 3 codoping in Sc 2 O 3 –ZrO 2 , the total doping concentration was fixed at 12 mol %. , In this high doping region, only cubic and rhombohedral phases are reported to exist in ScSZ. The present work studies the effect of Yb 2 O 3 codoping on the metastable tetragonal phases ( t ′ and t ″), which were found to exist in 8–9 mol % Sc 2 O 3 –ZrO 2 .…”