Micro-Raman spectroscopy on YBCO films during heat treatment

The oxygen content and the local oxygen arrangement of YBa2Cu3O7-x (YBCO) thin films grown on NdGaO3 substrates have been monitored by micro-Raman spectroscopy. The analysis was performed during the heat treatment of the sample in air, with temperatures Ta ranging between 20–300 °C. At Ta <220°C, the superconductivity of the samples was preserved, the critical temperature Tc being in the range of 86–90.7 K. At higher heating temperatures, the zero voltage state was suppressed due to the loss of oxygen. Evidence of fully oxygenated phase domains was nevertheless observed, proving the existence of a multiphase structure. The dramatic changes in the electrical characteristics are thus attributed to grain boundary region de-oxygenation, revealing the important role of planar-type defects on the transport properties of the films.