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

Abstract

Abstract La- and Ni-site cation transport was investigated by inter-diffusion couples in Sr- and Cu-substituted La 2 NiO 4+δ (LNO) systems. The diffusion couples between La 1.9 Sr 0.1 NiO 4+δ –Nd 1.9 Sr 0.1 NiO 4+δ , La 2 Ni 0.8 Cu 0.2 O 4+δ –Nd 2 Ni 0.8 Cu 0.2 O 4+δ and La 1.9 Sr 0.1 NiO 4+δ –La 1.9 Sr 0.1 CuO 4+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 La 1.9 Sr 0.1 NiO 4+δ –La 1.9 Sr 0.1 CuO 4+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.