Influence of B-site substituent Ce on thermophysical, oxygen diffusion, and mechanical properties of La2Zr2O7

Pyrochlore-type La2Zr2O7 (LZ) is a promising candidate for high-temperature thermal barrier coatings (TBCs). However, its thermal expansion coefficient and low fracture toughness are not optimal for such application and thus, need to be improved. In this study, we systematically report the effect of CeO2 addition on phase formation, oxygen-ion diffusion, and thermophysical and mechanical properties of full compositions La2(Zr1- xCex)2O7 (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1). La2(Zr1- xCex)2O7 exhibits a pyrochlore structure at x <= 0.3, while a fluorite structure is observed outside this range. With the increase in CeO2 content, thermal expansion coefficient and oxygen-ion diffusivity in La2(Zr1- xCex)2O7 are increased. Oxygen-ion diffusivity of La2(Zr1- xCex)2O7 is two orders of magnitude less than that of classical 8YSZ. Among La2(Zr1- xCex)2O7 compounds, La2(Zr0.7Ce0.3)2O7 and La2(Zr0.5Ce0.5)2O7 exhibit relatively low oxygen diffusivities. The composition La2(Zr0.5Ce0.5)2O7 presents the lowest thermal conductivity due to the strongest phonon scattering and also the highest fracture toughness due to the solid-solution toughening. The highest sintering resistance is achieved by the composition La2(Zr0.7Ce0.3)2O7 because of its ordered pyrochlore structure and high atomic mass of Ce. Based on these results, the compositions La2(Zr0.5Ce0.5)2O7 and La2(Zr0.7Ce0.3)2O7 are alternatives for classical 8YSZ for TBC materials operating at ul-trahigh temperatures.