Oxygenation mechanism of TSMG YBCO bulk superconductor

Abstract

For the first time isothermal thermogravimetric (TG) measurements of oxygen diffusion in to melt processed YBa2Cu3Oδ/Y2BaCuO5 (Y123/Y211 or YBCO) bulk samples were conducted in the temperature range 350 – 800°C. It is shown that the real time to a full sample oxygenation is much shorter than the calculated one assuming the bulk oxygen diffusion along the a/b-planes. It means that the diffusion distances in the oxygenated samples were much shorter at all temperatures of oxygenation then the halve sample size along the a/b-plane (0.1 cm). Estimated diffusion distances correspondent well with the spacing of the cracks formed during oxygenation. The kinetic law of virgin oxygenation at 350 and 400°C is changed during oxygenation and observed deviation from the typical parabolic dependence of the sample weight on time of isothermal oxygenation was related to oxygenation cracking during the sample oxygenation. The performed microstructural analysis of the samples studied confirmed that the change of oxygenation kinetics is accompanied with cracking. Developed oxygenation cracks along the {100} (c-cracks) and {001} (a/b-cracks) type planes play a crucial role in shortening the oxygenation time of single-grain TSMG YBCO bulk superconductors.