Influence of annealing at intermediate temperature on oxygen transport kinetics of Pr2NiO4+δ

Electrical conductivity relaxation (ECR) and oxygen permeation measurements were conducted, at 750 °C, to assess the long-term oxygen transport characteristics of the mixed ionic-electronic conducting Pr 2 NiO 4+ δ with a K 2 NiF 4 structure. The results show that the apparent values for the oxygen diffusion and surface exchange coefficients extracted from the data and the associated oxygen flux increase over 120 h by 1-2 orders of magnitude. The results of post-mortem X-ray diffraction analysis of the samples show partial to virtually complete decomposition of Pr 2 NiO 4+ δ under the conditions of the experiments to Pr 4 Ni 3 O 10+ δ , PrNiO 3− δ , Pr 6 O 11 , and traces of NiO. Pulse 18 O- 16 O isotopic exchange (PIE) measurements confirmed fast surface exchange kinetics of the higher-order Ruddlesden-Popper phase Pr 4 Ni 3 O 10+ δ and Pr 6 O 11 formed upon decomposition. Additional factors related to the microstructure, however, need to be considered to explain the observations. Decomposition of the layered Ruddlesden-Popper (RP) phase Pr 2 NiO 4+ δ into higher order phases during long-term annealing dramatically enhances oxygen transport.