Raman study of the effect of water vapor during low-temperature annealing on the structure and electrophysical properties of YBa2Cu3Oy

The effects of an interaction of YBa(2)Cu(3)o(y) (123) with water vapors at a temperature 200 degrees C on the structure and electrophysical properties of the compound have been examined by Raman spectroscopy. It has been found that the penetration of water into the 123-type causes the transition of the compound from an oxide to a hydride-oxide-hydroxide, which is accompanied with transformation to the 124 pseudotype phase. Direct evidence has been obtained for the incorporation of OH--groups in the 123-structure. After the interaction with water, the materials with high oxygen content (y >= 6.5) retain their superconductivity and exhibit two-magnon scattering in Raman spectra, which is not typical for them. Short-term recovery annealing followed by oxidation removes the water from the compound structure, which leads to the disappearance of the spin fluctuation spectra. At the same time, the structural defects are partially preserved. These manifest themselves through some peculiarities in the Raman spectra and are apparently pinning centers of magnetic vortices. A model of a splitting of the Cu-O chains and a formation of the 124-like phase in water-intercalated 123-structure has been proposed. This mechanism supposes the dissociation of the OH--groups and the filling in the copper vacancies by protons. (C) 2015 Elsevier B.V. All rights reserved.