In this work we attempt to give solution to apparently inconsistent results on grain boundary diffusion of Sr in 10GDC that we have found in our earlier diffusion experiments. The emphasis is placed on using of diffusion triplets: LSCF(porous)/10GDC(dense)/8YSZ(dense) that reproduce the driving forces for Sr diffusion found in solid oxide fuel cell (SOFC) real systems. The diffusion triplets were annealed at 1100 and 1200 degrees C for one week. Detailed analyses of the microstructure and elemental distributions unequivocally demonstrate the SrZrO3 formation along both the LSCF/10GDC and the 10GDC/8YSZ interfaces as the result of strontium and zirconium counter directional grain boundary diffusion through the 10GDC interlayer. Furthermore, micro-cracks in the 10GDC interlayer, formed during pre-annealing of the 10GDC/8YSZ layers, were also found to contribute to the SrZrO3 formation via surface diffusion. Thermodynamic considerations taking in account these microstructural features successfully explain, in terms of the chemical potential gradients developed across the 10GDC layer, why SrZrO3 is formed along both interfaces when grain boundary diffusion, or surface diffusion (along crack walls), become dominant compared to bulk diffusion through the 10GDC. (C) 2014 Elsevier B.V. All rights reserved.