YBa2Cu3O7-d (YBCO) was one of the first high temperature superconductorsdiscovered, and its superconducting properties are strongly dependent on oxygenstoichiometry. A large amount of work has been done on the variation of stoichiometryand its effect on the superconducting properties of the material. However, in spite of allthe work done, the results published in the literature are very scattered.This thesis presents a thermogravimetric study of oxygen diffusion in YBCO underisothermal and non-isothermal conditions and tries to reconcile the data available basedon the results obtained and taking into account the factors that may have affected thedata presented by other groups, such as the effects of the microstructure and thedifferent diffusion coefficients measured with the techniques used. An Arrheniusexpression for the chemical diffusion of oxygen has been calculated from the analysis ofisothermal oxygenation data, and it has been corroborated by a study of the nonisothermalexperiments carried out. This work includes the development of amacroscopic model for oxygen diffusion in YBCO based on the diffusion coefficientcalculated from experimental data. The model is used to simulate for the first timeoxygenations under both isothermal and non-isothermal conditions.The study of non-isothermal oxygenations has led directly to the design of novel coolingprocedures that can be introduced at the end of the processing stage of YBCO samples,producing highly oxygenated specimens in shorter times than for conventionalisothermal and ramped oxygenation procedures.The final section of this dissertation presents a study of the Direct Current Zoning effect.The generation of a mobile hot zone in a polycrystalline YBCO bar when passing acurrent across it is directly linked to the diffusion of oxygen ions in the material. Amechanism for the motion of the zone along the sample has been suggested. A computermodel has been developed to reproduce this process taking into account the motion ofions due to chemical diffusion and the potential difference established. The results fromthis model have corroborated the mechanism suggested and give for the first time theopportunity to study this phenomenon in more detail.
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