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Nuevas aproximaciones al estudio de la dinámica de la relajación dieléctrica en ferroeléctricos ordinarios y relajadores

  • Autores: Rafael Levit Valenzuela
  • Directores de la Tesis: José Eduardo García García (dir. tes.), Diego Alejandro Ochoa Guerrero (codir. tes.)
  • Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2019
  • Idioma: español
  • Materias:
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  • Resumen
    • Ferroelectric materials are endowed with fascinating functional properties from the technological point of view. Consequently, they have promoted the design of ferroelectric-based devices with applications in a vast range of industries. However, there are physical phenomena in these materials that represent a challenge for solid-state physics. Specifically, understanding the correlation between microstructure and functional properties, as well as the properties of the relaxation dynamics from the high sintering temperatures to the working temperatures. The likelihood of functional properties enhancement leads to countless studies on these subjects. This compendium of articles is based on the research of structural order from the crystallographic point of view, as well as on the study of the dielectric properties relaxation dynamics of ferroelectrics. The phenomenological Vogel-Fulcher-Tammann (VFT) equation has been used for decades to parameterize the dielectric relaxation dynamics of ferroelectrics. The first results of this work prove that this parameterization can be applied to the study of the dielectric anomalies exhibited by normal ferroelectrics at low temperatures, highlighting the dynamic nature of the relaxations and refuting previous hypotheses related to structural origin of this dielectric anomaly. Notwithstanding the good results of VFT in the study of dielectric relaxations, there is no physical theoretical microscopic description that justifies the prevalence of this empirical relationship over others. For example, the glassy transition studies in glasses, polymers, and other inorganic amorphous materials are carried on using different, though equally valid parameterizations. Precisely, the confirmation that there is none statistical criterion showing a prevailing parameterization to fit the dielectric relaxations is also an important result of this work. Since different parameterizations provide different explanations for the physical phenomena governing the dielectric relaxations, choosing a parameterization implies biasing the analysis of these physical phenomena. The above conclusion justifies the use of a new unbiased methodology, free of phenomenological models, to study the dielectric relaxations. The method is based on the direct experimental data processing, allowing to obtain the temperatures and coefficients that describe the dielectric relaxations. Hence, changes in the dynamical response and the freezing temperatures could be identified directly from data processing. Besides, as a novelty of this work, a new parameter associated with the compositional order of the relaxor systems is introduced. In fact, the introduction of this parameter and its relationship with the configurational entropy on the studied systems is one of the most reliable results of this work. Finally, a more general parameterization is proposed based on the Adam-Gibbs model and the Grüneisen index. The main advantage of the new equation is the use of only two fitting parameters to study the dielectric relaxations dynamics, similar to the famous Arrhenius equation. As a result of the universality of the proposed methodology and the new parameterization, the work accomplished in this compendium will be relevant for studying the relaxation dynamics in other ferroic systems.

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