The high-temperature superconductor EuBa2Cu3O6+x:role of thermal hystory on microstructure and superconducting properties

We present here combined resistivity and micro-Raman spectroscopy measurements for the superconductor EuBa2Cu3O6+x (Eu-123, EuBCO). We found an important dependence of microstructure and critical temperature on preparation temperature. We also show a strong orientation effect and a Tc of 93 K in samples prepared at high temperature relative to those prepared at lower temperature, which exhibit lower Tc, broad transitions, and no grain orientation. In addition, we show the influence of annealing conditions on superconducting properties by preparing samples with the same oxygen content (x = 0.38) but with various T and P(O2). The peculiar behavior of Eu-123 with temperature by considering a different hole injection sequence for Eu-123 with respect to Y-123 is explained. Micro-Raman measurements seem to support this hypothesis.