Defect‐chemical Investigations of Defined YBa2Cu3Ox‐Superconductors

Using our K2CO3‐method we succeeded in preparing highly oriented ceramics and large crystals tolerating unusually high currents. Both results and our techniques to determine precisely the redox‐state and to improve durability against humid atmosphere are briefly reviewed. We also report on the possibility of an elemental disorder in the Ba‐ and Y‐sublattice. The use of oriented samples allowed us to measure the anisotropy of the electronic conductivity. At higher temperatures where equilibrium with the ambient oxygen containing atmosphere is achieved, both the ionic conductivity and the chemical oxygen diffusion coefficient are determined by a chemical and an electrochemical relaxation technique. Finally, a defect model is proposed that takes account of the high non‐stoichiometries and explains the oxygen partial pressure dependence of the electronic conductivity observed in our experiments as well as in the literature.