YBa2Cu3O6+d-originated attraction force giving rise to Meissner effect   at 300 K
  The exposure of YBCO to an air atmosphere at first at pH2O = 110 Pa and then at pH2O = 1 kPa has been used for uncharacteristic and unusual properties of YBCO to be observed. Among them there was an increased reactivity of YBCO with respect to water. Besides, it was experimentally obtained extremely excessive weight gain of hydrated YBCO samples that was not corresponding to the quantity of the absorbed water. Finally, we obtained the significant negative value of the room-temperature (RT) magnetic susceptibility in conventional magnetic study of the hydrated YBCO that was confirmed by the direct observation of decreasing weight of the same samples that were suspended above the source of controlled magnetic field (DC mode) at RT. All the results were explained on the basis of an approximate idea that there is a certain source of attractive force inside YBCO, acting on surrounding particles and bodies. 
A. V. Fetisov and R. I. Gulyaeva
cond-mat.mtrl-sci