Macro-cracking in melt-grown YBaCuO superconductor induced by surface oxygenation

We have shown that oxygenation of the melt-grown YBa 2 Cu 3 O 7 /Y 2 BaCuO 5 single grain superconductors is associated with the formation of macro-cracks parallel to the a / b -plane. The origin of these cracks is associated with tensile stress induced into the oxygenated surface layer due the c -lattice parameter shortening. The critical strain calculated according to Thoules's model for the cracking of brittle films on an elastic substrate suggests that the macro-cracking starts much earlier than the formation of the homogeneous layer of equilibrium oxygen content at the surface.