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

Abstract

The present work studies the effect of thermal aging and 1 mol % Yb 2 O 3 codoping on the metastable tetragonal phases present in 8−9 mol % Sc 2 O 3 −ZrO 2 . Dense ceramic discs of xYb 2 O 3 −(y − x)Sc 2 O 3 −(100− y)ZrO 2 (x = 0 and 1 mol %; y = 8 and 9 mol %) are prepared using conventional solid-state route. XRD, TEM and Raman spectroscopy analysis confirmed the metastable t′phase in 8Sc 2 O 3 −92ZrO 2 and t″-phase in 9Sc 2 O 3 −91ZrO 2 . Although t′-phase is retained on Yb 2 O 3 codoping in 8Sc 2 O 3 −92ZrO 2 , the tetragonality reduces. However, codoping does not affect the t″-phase present in 9Sc 2 O 3 −91ZrO 2 . After aging at 650 °C for 2000 h in air, a decrease in unit-cell parameters ratio and weak XRD peak-splitting are observed in 8Sc 2 O 3 −92ZrO 2 and 1Yb 2 O 3 −7Sc 2 O 3 − 92ZrO 2 suggesting a reduction in unit-cell tetragonality, though t′-phase still exists in both the compositions. In compositions possessing t″-phase, a slight lattice contraction is detected on thermal aging. The tetragonality induced by oxygen-ion shuffling inside the unit-cell increases after aging in all the compositions. This shuffling is lower in the aged sample of 1Yb 2 O 3 − 7Sc 2 O 3 −92ZrO 2 compared to 8Sc 2 O 3 −92ZrO 2 . However, it remains similar in both 1Yb 2 O 3 −8Sc 2 O 3 −91ZrO 2 and 9Sc 2 O 3 − 91ZrO 2 , suggesting a negligible codoping effect on t″-phase. These results demonstrate the effectiveness of Yb 2 O 3 codoping in lowering the tetragonality of metastable t′-phase, which may positively affect the conductivity of ScSZ.

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

“…The Raman spectrum of 10ScSZ crystals contains bands corresponding to a mixture of rhombohedral and tetragonal t phases [26]. Thus, the results obtained by X-ray diffraction and Raman spectroscopy confirm previously published data on the positive effect of the addition of Yb 2 O 3 on the stabilization of the cubic (pseudocubic t ) phase [19].…”

“…The Raman spectrum of 10ScSZ crystals contains bands corresponding to a mixture of rhombohedral and tetragonal t″ phases [26]. Thus, the results obtained by X-ray diffraction and Raman spectroscopy confirm previously published data on the positive effect of the addition of Yb2O3 on the stabilization of the cubic (pseudocubic t″) phase [19]. Figure 3 shows typical impedance spectra in Nyquist coordinates for single-crystal solid electrolyte membranes with compositions of 9Sc1YbSZ and 8Sc2YbSZ, measured at temperatures of 624 and 1123 K, respectively.…”

“…Of the electrolytic membranes based on zirconium dioxide, ZrO 2 –Sc 2 O 3 (ScSZ) solid solutions have the highest conductivity; therefore, much attention has been paid to the study of the processes of high-temperature degradation of the conductivity of these materials [ 16 , 18 , 19 ]. It was shown that annealing at 1000 °C for 6000 h of 8ScSZ ceramic samples with a cubic fluorite structure led to a significant degradation in conductivity, while no change in conductivity was observed for rhombohedral samples of 11ScSZ and 12ScSZ [ 18 ].…”

“…As a rule, yttrium oxide or oxides of other rare earth elements are introduced into zirconium dioxide stabilized by scandium oxide, which has a high oxygen ion conductivity. The study of the aging of such ceramic materials has been carried out in a number of works [ 13 , 16 , 19 , 20 ].…”

Stability of the Structural and Transport Characteristics of (ZrO2)0.99−x(Sc2O3)x(R2O3)0.01 (R–Yb, Y, Tb, Gd) Electrolytic Membranes to High-Temperature Exposure

“…A number of works are devoted to the study of the high-temperature degradation of ZrO 2 -Sc 2 O 3 solid solutions [ 16 , 17 , 18 , 19 , 20 , 21 ]. The following mechanisms were considered reasons for degradation: phase changes leading to the formation of inclusions of a low-conductivity tetragonal phase in a cubic matrix [ 16 ]; the formation of various associates of defects [ 17 ]; and local ordering of oxygen ions and oxygen vacancies [ 18 ].…”