Collective defect formation in the high-temperature superconductor YBa2Cu3O7 under the influence of adsorbed water molecules |
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Authors: | B M Gorelov |
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Institution: | (1) Institute of Surface Chemistry, National Academy of Sciences of Ukraine, 252022 Kiev, Ukraine |
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Abstract: | The mechanisms for defect formation stimulated by the adsorption of water molecules in the surface of YBa2Cu3O7 ceramic are studied, together with the types of defects and their distributions. It is found that a water layer physically
bound to the surface reduces the rates of annihilation and capture of positrons, changes the amount of barium and copper on
the surface by a factor of two, and inhibits diffusive jumps of nickel atoms. A layer of adsorbed water excites subthreshold
formation of 1021 cm−3 interstitial Ba and Cu1 atoms and transitions of oxygen from O1 to O5, and vice versa in the volume of crystallites, and the migration of defects and accumulation of Ba atoms in the surface layer, which block
diffusive jumps of Ni within the volume of the crystals. These effects are related to the excitation of collective, low-frequency
weakly damped motion of heavy holes in the crystal volume when defects are formed on the surface by physically adsorbed H2O molecules, which is accompanied by Coulomb repulsion of cations from intermediate layers into interstitials and the migration
of defects in the field of the collective excitations.
Zh. éksp. Teor. Fiz. 116, 586–603 (August 1999) |
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