Use of RBS and Raman spectroscopy to study oxygen mobility in YBaCuO thin films by 18O tracing experiments

Abstract The 18 O tracer technique is particularly well adapted to study the mobility of oxygen and to evidence the presence of oxygen sites of different energies. The annealing experiments in a pure oxygen atmosphere enriched to > 98% 18 O were performed for 19 h at 200 mbar and at three different temperatures: 350, 450 and 650°C. At 350, and at 450°C the orthorhombic phase was totally preserved (Y 1 Ba 2 Cu 3 O 7 ), whereas at 650°C the nominal oxygen composition was O 6,4 and corresponds to the orthorhombic-te-tragonal transition. All the experiments were performed using YBaCuO samples deposited on MgO substrate by laser ablation or cathodic sputtering. The samples were characterized by X-rays and T c measurements. Their composition and structure were studied by RBS, NRA and ion channeling. The 18 O distribution was studied using the resonant nuclear reaction at 629 keV. The localization in the YBaCuO structure of the 18 O atoms was studied using Raman spectroscopy. It was found that the 18 O uptake at 350°C leads to the formation of a thin surface layer (15 nm) enriched to about 30% whereas the volume enrichment appears to be low (3.5%) and quasi-constant. This result suggests that the 18 O exchange at 350°C is controlled by the diffusion. The reoxidation in 18 O atmosphere of partially reduced sample is shown to be much quicker than that observed by direct exchange. It was found that the 18 O exchange at 450°C leads to a quasi-constant 18 O profile (enrichment to 70% was observed after annealing during 19 h). The Raman spectroscopy showed that the annealing at 450°C induced equivalent exchange in CuO 2 planes and of the bridging oxygen. The annealing at 650°C leads to a total exchange between 16 O and 18 O.