Effect of LSCF Microstructure on GDC Interlayer Stability and Cation Diffusion in Porous and Dense LSCF/GDC/YSZ Triplets

The long-term stability of GDC interlayer as a reaction barrier between La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathode and polycrystalline yttria-stabilized zirconia YSZ substrate is essential in improving the performance of the LSCF cathode at the required operating temperature. However, the formation of resistive phases, especially SrZrO₃ at the interfaces that affects the performance of LSCF cathode is still difficult to mitigate even with the use of GDC interlayer. For this purpose, we systematically evaluated the long-term stability of GDC interlayer by performing cation diffusion experiments using porous and dense LSCF layers. The dense LSCF/GDC/poly-YSZ has homogeneous interfaces, enabling simpler analysis of interface stability and cation diffusion. In both heterostructures, a ~1.0 µm–thick, dense GDC interlayer was utilized which was prepared by PLD with subsequent annealing at 1300°C for 5h. The LSCF/GDC/YSZ heterostructures were then annealed in air at temperatures ranging from 800°C to 1000°C starting from 168 hours to 731 hours. We find that in porous LSCF, the GDC interlayer characterized by significant formation of pores while severe microcraking occurred in dense LSCF after prolonged annealing. We also observed shrinkage of GDC interlayer at elevated temperature in porous samples compared to dense. At high sintering temperature, the Sr and Zr diffusivity along the grain boundaries of GDC interlayer is the dominant diffusion pathway in porous LSCF/GDC/YSZ leading to the formation of SrZrO₃, while for dense LSCF/GDC/YSZ, the cracks or crack–walls in the GDC interlayer are fast diffusion paths for cation diffusion. We also observed that the lateral growth of SrZrO₃ at the GDC/YSZ interface is influenced by the microstructure of GDC interlayer and sintering temperature. Our results show that the interfacial microstructure of LSCF/GDC plays an important role in understanding the formation of SrZrO₃ in LSCF/GDC/YSZ triplets as well as the effectiveness of GDC interlayer as a reaction barrier.