High-temperature superconducting oxides: A thermodynamic and impurity study

The author has studied the newly discovered high temperature superconducting systems, pure YBa2Cu3O7, oxygen deficient YBa2Cu3O7-δ with δ = 0.05, 0.15, 0.25, 0.35, and 0.45, and YBa2(Cu1-xMx)3O7-δ with M = Zn, Co, Ga and Al. The measurements that have been made include X-ray diffraction, thermal gravimetric analysis (TGA), electron paramagnetic resonance (EPR), temperature and magnetic field dependence of specific heat, and the temperature dependence of resistivity and magnetic susceptibility. From these studies, a clearer understanding of the importance of the Cu-O chains vs Cu-O planes on the superconductivity of YBa2Cu3O7-δ is established. In addition, thermodynamic studies, e.g., the specific heat vs temperature, seems to indicate that the YBa2Cu3O7-δ system is a weak coupling BCS superconductor thus indicating the mechanisms other than phonons alone are contributing to the pairing interactions. In addition, as Tc is depressed with increasing x in the YBa2(Cu1-xAnx)3O7-δ system, the specific heat anomaly at Tc scales according to that expected using a weak coupling BCS theory