Structural, surface and oxygen transport properties of Sm-doped Nd nickelates

Ruddlesden – Popper phases are promising materials for solid oxide fuel cell/electrolyzer air electrodes, oxygen separation membranes and other electrochemical devices due to their high oxygen mobility provided by a cooperative mechanism of oxygen migration involving both regular and highly-mobile interstitial oxygen. This work aims at studying structural, surface and oxygen transport properties of Sm-doped Nd nickelates sintered in a furnace at the temperatures in the range of 800–1250 °C and using electron beams at the temperatures in the range of 1150–1250 °C. Nd_2-xSm_xNiO_4+δ, x = 0.2 and 0.4 are synthesized by a modified Pechini technique and characterized by X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed isotope exchange of oxygen with C¹⁸O₂ in a flow reactor. The phase composition studies show the ability to obtain single-phase materials at certain sintering conditions. Nd/Sm ratio on the surface is close to stoichiometric one, while (Nd + Sm)/Ni ratio on the surface is below stoichiometric. Such materials possess a high oxygen mobility (D^⁎ up to ∼10⁻⁷ cm²/s at 700 °C).