Influence of the superconducting state of YBa2Cu3O7-x ceramics on the nature of collisions between paramagnetic dioxygen molecules and the ceramic surface

Measuring the heating rate of well prepared superconducting ceramics YBa2Cu 3O7-x in atmospheres of dinitrogen and dioxygen at 77.4-92 K, we have shown that the paramagnetic dioxygen molecules provide a less effective heat tra nsfer to the YBa2Cu3O7-x than the diamagnetic dinitrogen molecules. It was suggested that the phenomenon results from the predominantly elastic collis ions between the paramagnetic dioxygen molecules and the ceramic surface. T he elasticity is induced by the superconducting state of the material posse ssing a high value of the lower critical field H-c1g = 1.04 x 10(4) A m(-1) and with the mean size for the granules r(ms) similar to 40 mu m. If the v alue of applied field H-a > H-c1g the elastic collisions between dioxygen m olecules and the superconductor surface are suppressed. For the superconduc tor with a low value of H-c1g = 1.4 x 10(3) A m(-1) and r(ms) similar to 10 mu m there are no elastic collisions of dioxygen molecules with the superc onducting surface. We propose that this phenomenon is associated with inter action between the paramagnetic moment of the dioxygen molecule and the mag netic flux 'frozen' into the superconductor.