Oxygen diffusion and phase transformation in Y1Ba2Cu3Ox

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Abstract
Detailed in situ x‐ray diffraction experiments, differential scanning calorimetry, and thermogravimetrical analyses are performed during annealing of superconducting Y1Ba2Cu3Ox samples in order to study the influence of the oxygen diffusion on the structure and structural changes of these alloys. The superconducting properties before and after annealing are checked via resistivity measurements. Annealing in vacuum leads to an irreversible and diffusion controlled phase transformation from the superconducting orthorhombic to the semiconducting tetragonal perovskite structure. For small heating rates, the transition starts at about 550 °C. With increasing heating rates the diffusion mechanism causes a delayed onset and a broadening of the temperature regime of the transition. The interdiffusion constant D(700 °C) for oxygen in Y1Ba2Cu3Ox is about 10−12 cm2/s. Annealing at 550 °C in oxygen atmosphere regains the orthorhombic superconducting phase with its properties.