Modification of Ruddlesden-Popper-type Nd2-xNi0.75Cu0.2M0.05O4±δ by the Nd-site cationic deficiency and doping with Sc, Ga or In: Crystal structure, oxygen content, transport properties and oxygen permeability

Nd2-xNi0.75Cu0.2M0.05O4 +/-delta (x = 0( )and 0.1; M = Sc, Ga, and In) Ruddlesden-Popper-type oxides are obtained by a sol-gel route and characterized concerning phase composition and crystal structure. It is found that the largest In3+ cannot be effectively introduced into the structure, while Nd stoichiometric and cation-deficient Nd2-xNi0.75Cu0.2M0.05O4 +/-delta and Nd2-xNi0.75Cu0.2M0.05O4 +/-delta (x = 0; 0.1) can be obtained as single-phase materials. Systematic characterization of the crystal structure at high temperatures, oxygen content, as well as transport properties reveals that while the Nd-site deficiency has rather negligible influence on the structure, it causes a substantial decrease of the oxygen content, which at high temperatures leads to a change of the dominant type of defects from the oxygen interstitials to the vacancies for Nd1.9Ni0.75Cu0.2Sc0.05O4 +/-delta and Nd1.9Ni0.75Cu0.2M0.05O4 +/-delta. The Nd-site deficiency also causes a decrease of the total conductivity. Importantly, all the examined materials exhibit full chemical stability in CO 2 atmosphere, which together with moderate thermal expansion makes them good candidates for the oxygen transport membranes, which can be used e.g. in the air separation technologies. The selected Sc- and Ga-doped compounds evaluated as ceramic membranes show relatively high oxygen fluxes, with the highest value of 0.78 mL cm(-2) min(-1) at ca. 880 degrees C registered for 0.9 mm thick, dense Nd1.9Ni0.75Cu0.2M0.05O4 +/-delta membrane.

Automated summary

Ruddlesden-Popper-type oxides Nd2-xNi0.75Cu0.2M0.05O4 +/-delta (where x = 0 and 0.1; M = Sc, Ga, and In) were synthesized via a sol-gel method and characterized. Materials with Nd-site deficiency show potential applications as oxygen transport membranes with relatively high oxygen fluxes.