Electrical conductivity and oxygen exchange kinetics of La2 NiO4+δ thin films grown by chemical vapor deposition

Epitaxial c -axis oriented La2 NiO4+δ films were deposited onto SrTiO3 and NdGaO3 substrates by the pulsed injection metal organic chemical vapor deposition technique. Experimental conditions were optimized in order to accurately control the composition, thickness, and texture of the layers. X-ray diffraction was used to confirm the high crystalline quality of the obtained material. Electrical characterizations were performed on thin (50 nm) and thick (335 nm) layers. The total specific conductivity, which is predominantly electronic, was found to be larger for the thinner films measured (50 nm), probably due to the effect of the strain present in the layers. Those thin films (50 nm) showed values even larger than those observed for single crystals and, to our knowledge, are the largest conductivity values reported to date for the La2 NiO4+δ material. The oxygen exchange kinetics was studied by the electrical conductivity relaxation technique, from which the surface exchange coefficient was determined.