Cation transport in Sr and Cu substituted La2NiO4+δ studied by inter-diffusion

La- and Ni-site cation transport was investigated by inter-diffusion couples in Sr- and Cu-substituted La2NiO4+δ (LNO) systems. The diffusion couples between La1.9Sr0.1NiO4+δ-Nd1.9Sr0.1NiO4+δ, La2Ni0.8Cu0.2O4+δ-Nd2Ni0.8Cu0.2O4+δ and La1.9Sr0.1NiO4+δ-La1.9Sr0.1CuO4+δ were annealed for 200-643 h in dry air at 950-1300 °C. Electron Probe Micro Analysis (EPMA) was used to obtain the concentration profiles of the inter-diffusing cations. The solution of Fick's second law for constant source and the Whipple-Le Claire equation were applied for analysis of bulk and grain boundary diffusion, respectively. The obtained results are in good agreement with our previous investigation of cation diffusion in un-substituted LNO, where La- and Ni-site cations have essentially comparable diffusivities in the bulk material and Ni-site diffusion is strongly enhanced along grain boundaries. The enhanced grain boundary diffusion has been visualised by elemental mapping of the cross-section of La1.9Sr0.1NiO4+δ-La1.9Sr0.1CuO4+δ diffusion couples. The extracted activation energies are 223 ± 15 and 267 ± 14 kJ/mol for La-site bulk diffusion in Sr- and Cu-substituted LNO, respectively, and 446 ± 43 and 369 ± 31 kJ/mol for Ni-site bulk and grain boundary diffusion, respectively, in Cu-substituted LNO. Possible causes for similar bulk and enhanced grain boundary diffusivities of the Ni-site despite higher activation energies as compared with La-site bulk diffusion are discussed.