OPTICAL EMISSION SPECTROSCOPY OF A SUPERSONIC LOW-PRESSURE PLASMA REACTOR USED TO SYNTHESIS SOFC CATHODES THIN LAYERS

A low pressure plasma reactor equipped with a supersonic nozzle was employed to synthesize thin perovskite layers La1-xSrx(Mn, Co)O3±δ on the Solid Oxide Fuel Cell (SOFC) electrolyte from a solution containing nitrates. To determine the role of plasma species in transformation of nitrates into perovskite, Optical Emission Spectroscopy (OES) measurements have been performed on the Ar/O2 discharge during the deposition. At each injection of nitrates precursors, OES have detected species such as Ar*, O from the dissociation of O2, and OHº from the decomposition of water. The electronic temperature (2.5 eV), the excitation temperature of Ar (8900 K) and the rotational temperature of OHº (360 K) have been measured. The results have confirmed that the nitrates are transformed mainly by oxidization reactions at low temperature using O and OHº. This plasma process allows a thin perovskite layer formation without undesirable phases (La(OH)3...), that are generally produced in thermal processes.