Ultralow oxygen ion diffusivity in pyrochlore-type La2(Zr0.7Ce0.3)2O7

Abstract Thermally grown oxides (TGOs) at the ceramic top-coat/metallic bond-coat interface are a pressing challenge in advanced thermal barrier coating (TBC) systems as they can affect the performance and service lifetime of TBCs. Thus, developing novel TBC materials with ultralow oxygen ion diffusivity is very urgent. In this study, we reported the diffusive properties of oxygen ions in a novel pyrochlore-type La2(Zr0.7Ce0.3)2O7 (LZ7C3) material. The measured ionic conductivity and atomistic simulation revealed that the oxygen ion diffusivity in LZ7C3 grains is two orders of magnitude lower than that in conventional 8 wt.% yttria-stabilized zirconia (8YSZ) grains. This is due to the relatively high energy barrier for oxygen hopping in LZ7C3. In addition, it was found that enhancing the order distribution of cations is a strategy to reduce the intrinsic oxygen diffusion of pyrochlore-type oxides. On the other hand, we observed that La3+ cations segregate at the grain boundaries (GBs) of LZ7C3, which results in the electrostatic potential at GBs being comparable to that in the bulk. Furthermore, we found that the oxygen ion diffusion is facilitated at the GBs of LZ7C3 due to the stretched O–Zr/Ce bond and the low coordination at GBs. However, the segregations of Y3+ cations and the increase in the number of oxygen vacancies resulted in the formation of an electrostatic layer at the GBs of 8YSZ, which shielded the oxygen ion diffusion. Despite this, the oxygen ion diffusivity in LZ7C3 was still considerably less than that in conventional 8YSZ. This study offers a stepping stone toward utilizing pyrochlore-type LZ7C3 materials as advanced TBCs at high temperatures.