Oxygen stoichiometry and structure of YBa2Cu3O7−δ and their relation to superconductivity

Thermogravimetric curves of the superconducting samples (0.0 ≤ δ 〈0.5) of YBa2Cu3O7−δ are shown to be characteristically different from those of the non-superconducting samples (δ⋍0.5–1.0). The variation of Tc (from resistivity measurements) with δ confirms for a change from chain-super-conductivity to plane-superconductivity. Bands found in bright or dark field electron micrographs are shown to arise for different orientations of the [CuO2]∞ planes, causing oxygen enrichment in the boundaries. A new defect with missing Y-rows is found in the images of Y1−xBa2Cu3O7.