TIME-RESOLVED NEUTRON-DIFFRACTION INVESTIGATION OF THE EFFECT OF HYDROGEN ON THE HIGH-TC SUPERCONDUCTOR YBA2CU3O7-DELTA

The results of a time-resolved neutron diffraction investigation of the interaction of hydrogen flow with the high-T(c) superconductor YBa2CuO7-delta are presented. The experiment was carried out on the TOF diffractometer DN-2 at the reactor IBR-2 in Dubna. Hydrogenation was performed on small pieces of 1-2-3 ceramics which were enclosed inside a quartz tube. The sample was heated up to 350-degrees-C at a constant rate of 5-degrees-C/min. Diffraction patterns were collected every 3 min within the d(hkl)-interval of 1-20 angstrom. Up to 220-degrees-C the refinement yielded the well-known orthorhombic phase of the 1-2-3 structure without any remarkable reduction of the (b - a)/(a + b) ratio. Below this temperature the only change in the specimen was a gradual increase of the incoherent background which occurred even at room temperature. Once the temperature of 220-degrees-C was reached, sample degradation took place as evidenced by precipitation of metallic copper, a drastic increase of background and widening of the diffraction peaks. Simultaneously, the occupancy of O(4) + O(5) sites fell to 0.6. No evidence was found for the formation of a solid solution of hydrogen in 1-2-3 structure.