Oxygen distribution in YBa2Cu3O7-x single crystals with x > 0.5

The structure of YBa2Cu3O7-x high-temperature superconducting single crystals with an average oxygen concentration corresponding to x = 0.7 is investigated by transmission electron microscopy. It is demonstrated that this compound is characterized by an inhomogeneous oxygen distribution throughout the crystal: the specimen is divided into blocks with different oxygen concentrations. The oxygen concentration varies from block to block over the interval 0.5 ≤ x ≤ 1. The characteristic block size is ∼ 100 x 10 x 20 nm3. Annealing at T = 370 degree C accompanied by diffusion of the oxygen over a distance substantially exceeding the block size could not eliminate the nonuniform oxygen distribution