A thermogravimetric study of oxygen diffusion in YBa2Cu3O7-d
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Authors
Vazquez-Navarro, Maria Dolores
Date
1998-08Awarding Institution
University of Cambridge
Author Affiliation
Department of Materials Science and Metallurgy
Qualification
Doctor of Philosophy (PhD)
Language
English
Type
Thesis
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1393618 bytes
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Vazquez-Navarro, M. D. (1998). A thermogravimetric study of oxygen diffusion in YBa2Cu3O7-d (Doctoral thesis). https://doi.org/10.17863/CAM.14202
Abstract
YBa2Cu3O7-d (YBCO) was one of the first high temperature superconductors
discovered, and its superconducting properties are strongly dependent on oxygen
stoichiometry. A large amount of work has been done on the variation of stoichiometry
and its effect on the superconducting properties of the material. However, in spite of all
the work done, the results published in the literature are very scattered.
This thesis presents a thermogravimetric study of oxygen diffusion in YBCO under
isothermal and non-isothermal conditions and tries to reconcile the data available based
on the results obtained and taking into account the factors that may have affected the
data presented by other groups, such as the effects of the microstructure and the
different diffusion coefficients measured with the techniques used. An Arrhenius
expression for the chemical diffusion of oxygen has been calculated from the analysis of
isothermal oxygenation data, and it has been corroborated by a study of the nonisothermal
experiments carried out. This work includes the development of a
macroscopic model for oxygen diffusion in YBCO based on the diffusion coefficient
calculated from experimental data. The model is used to simulate for the first time
oxygenations under both isothermal and non-isothermal conditions.
The study of non-isothermal oxygenations has led directly to the design of novel cooling
procedures that can be introduced at the end of the processing stage of YBCO samples,
producing highly oxygenated specimens in shorter times than for conventional
isothermal 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 a
current across it is directly linked to the diffusion of oxygen ions in the material. A
mechanism for the motion of the zone along the sample has been suggested. A computer
model has been developed to reproduce this process taking into account the motion of
ions due to chemical diffusion and the potential difference established. The results from
this model have corroborated the mechanism suggested and give for the first time the
opportunity to study this phenomenon in more detail.
Keywords
oxygen diffusion, YBCO, superconductivity, thermogravimetric
Identifiers
This record's DOI: https://doi.org/10.17863/CAM.14202