Systematics of Phase Transition and Mixing Energetics in Rare Earth, Yttrium, and Scandium Stabilized Zirconia and Hafnia

Abstract

Energetics of rare earth, yttrium, and scandium stabilized zirconia and hafnia have been systematically investigated by oxide melt solution calorimetry. The enthalpies of formation with respect to the oxide end members were simultaneously fit to a quadratic function to extract interaction parameters and enthalpies of transition of the oxide end members to the fluorite structure. ZrO2–SmO1.5 and HfO2–SmO1.5 show the most exothermic enthalpies of formation and interaction parameters, whereas ZrO2–ScO1.5 has the least exothermic enthalpy of formation and interaction parameter. This suggests that the ZrO2–ScO1.5 system shows the least short range order among all investigated systems, consistent with its high ionic conductivity. The extrapolated enthalpy of transition of the rare earth oxide end members to the cubic fluorite structure increase to more endothermic values with decreasing cation size. The γ‐cubic fluorite phase transition in ZrO2–ScO1.5 was investigated by differential scanning calorimetry (DSC). The phase transition is reversible, occurs at 1000°–1200°C and shows hysteresis (∼100°C). The enthalpy of transition is endothermic on heating and increases from 1.7±0.1 kJ/mol (22 mol% ScO1.5) to 2.9±0.2 kJ/mol (30 mol% ScO1.5).

Up-Date of a Thermodynamic Database of the ZrO2-Gd2O3-Y2O3-Al2O3 System for TBC Applications

“…The tie-lines in the ZrO 2 -Gd 2 O 3 -Al 2 O 3 system were used to maintain consistency with the isothermal section at 1523 K [15] by adjusting the enthalpy of formation of GdAM phase. The calculated thermodynamic data for the Gd 2 O 3 -Al 2 O 3 and ZrO 2 -Gd 2 O 3 systems in comparison with experimental data [16,24,[43][44][45][46][47] are given in Table 4. Thermodynamic descriptions of the ZrO 2 -Al 2 O 3 [15,25] and …”

“…New heat capacity measurements of pyrochlore Gd 2 Zr 2 O 7 [14] are within uncertainty limits of data derived by Wang [23] based on his own measurements and the data of Lutique et al [24] Therefore the heat capacity data of Gd 2 Zr 2 O 7 was accepted to be the same as from Wang [23] The thermodynamic description of fluorite from Wang [23] appeared to be in good agreement with new solution calorimetry data for compositional dependence of enthalpy of formation of fluorite by Simoncic and Navrotsky. [16] Therefore the data of Wang [23] for fluorite was accepted in the Basic and Applied Research: Section I present study. The parameters of pyrochlore were re-assessed to be consistent with the description of pyrochlore in the ZrO 2 -La 2 O 3 -Al 2 O 3 system.…”

“…À11170 À10400 [16] x = 0.54 À11197 À11100 [16] x = 0.65 À7412 À7800 [16] 298.15 S(Pyr) Gd 2 Zr 2 O 7 263.68 263.4 [24] (a) Value of Ref 46 was corrected taking into account difference in enthalpy of formation of ZrO 2 [23] Basic and Applied Research: Section I Journal of Phase Equilibria and Diffusion Vol. 32 No.…”

“…Solution calorimetry measurements of the heat of formation of the fluorite phase in the ZrO 2 -Gd 2 O 3 system became available recently. [16] Therefore a re-assessment of the database is necessary. The thermodynamic parameters of the ZrO 2 -Y 2 O 3 -Al 2 O 3 system were already re-assessed by Fabrichnaya et al [17] The thermodynamic database for the ZrO 2 -Gd 2 O 3 -Y 2 O 3 -Al 2 O 3 system allows one to evaluate the thermal stability of the coating and its stability during thermal cycling.…”

Assessment of thermodynamic functions in the ZrO2–Sm2O3–Al2O3 system

“…Recently the thermodynamic assessment of the ZrO 2 -Sm 2 O 3 system was published by Wang et al [12] who applied sublattice models for liquid and solid phases. Wang et al [12] used his own experimental data along with literature data for phase equilibria [13][14][15][16][17][18] and calorimetric data [12,19,20] for the ZrO 2 -Sm 2 O 3 system. The thermodynamic parameters of the Sm 2 O 3 -Al 2 O 3 system were assessed by Wu and Pelton [21] using the quasichemical model for the liquid phase, which is not compatible with the ionic liquid model which was successfully applied to ZrO 2 -based systems [22][23][24][25][26][27].…”