Synthesis and electrical properties of Ln2CuO4+δ (Ln: Nd or La) mixed conductor sputter deposited coatings

Nd(2)CuO(4) and La(2)CuO(4) are potential candidates as cathode material for intermediate temperature-solid oxide fuel cells. Nd-Cu and La-Cu oxides were co-sputtered on rotating substrates from metallic La, Nd and Cu targets in the presence of a reactive argon-oxygen gas mixture. Structural and chemical features of these films have been determined by X-ray diffraction and energy-dispersive spectroscopy. Their electrical resistivity was measured using the four-point probe method. As-deposited Nd-Cu based coatings are amorphous and, after annealing, crystallise in K(2)NiF(4+) (delta) -type structure for Nd/Cu atomic ratio of 2, with more or less Nd(2)O(3) or CuO, depending on whether Nd or Cu is in excess, respectively. As-deposited La-Cu based coatings are also amorphous and crystallise in La(2)CuO(4) for La/Cu > 2 or in LaCuO(3 +/-delta) perovskite-type structure when Cu is in excess. The electrical measurements show a clear relation between resistivity and structure of the coatings. After annealing, crystallised neodymium-based coatings show higher resistivity than lanthanum-based ones. Finally, LaCuO(3 +/-delta) exhibit higher resistivity than La(2)CuO(4).