Orthorhombic YBCO-123 ceramic oxide superconductor: Structural, resistive and thermal properties

Two YBa2Cu3O7-x, materials (YBCO-I sintered at 1000 degrees C, and YBCO-II sintered at 960 degrees C and following special cooling programs) belonging to the orthorhombic system were obtained. YBCO-I has a complete volume texture, while for YBCO-II it is only on sample surface. On heating in air (with 10 K min(-1) in the temperature range 20-1000 degrees C), two endothermic processes are recorded on DSC curves (of YBCO-II) and they are due to oxygen diffusion from O1 to O5 sites, and then to the release into the environment; second endothermic effect is attributed to the decomposition reaction. Different behaviour is encountered on heating in argon: an endothermic process in two steps; continuous mass decrease (oxygen loss) during argon cooling is recorded on the thermo-gravimetric curve. In argon atmosphere, the obtained material shall correspond to the chemical composition: YBa2Cu3O6.77, while in air atmosphere, the maximal composition than may be obtained is: YBa2Cu3O6.88. The barrier energies from Arrhenius plots of resistivity vs. temperature (91-93 K) show 2D (YBCO-I) and 3D (YBCO-II) behaviour for the thermally activated flow of melted vortex lattice, below the critical temperature.