Ultra-wide temperature dielectric stability and polar nanoregions dynamics in 0.6Bi(Mg0.5Ti0.5)O3-0.4Ba0.8Ca0.2TiO3-based ceramics

• Autores: Chen Kaiyuan
• Directores de la Tesis: Senén Lanceros Méndez (dir. tes.), Qi Zhang (codir. tes.), Miren Gotzone Barandika Argoitia (tut. tes.)
• Lectura: En la Universidad del País Vasco - Euskal Herriko Unibertsitatea ( España ) en 2025
• Idioma: inglés
• Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología de Materiales por la Universidad del País Vasco/Euskal Herriko Unibertsitatea
• Calificación: Notable
• Materias:
  • Física
• Enlaces
  • Tesis en acceso abierto en: ADDI
• Resumen

  • To enhance the applicability of materials in modern electronics, understanding local structure and physical properties is crucial for fundamental research. Over the past two decades, (1-x)BaTiO3-xBiMeO3-based ceramics, where Me represents single or averaged of B-site ions, have garnered significant attention for developing high permittivity dielectrics suitable for elevated operating temperatures and/or electric fields. Members of the (1-x)BaTiO3-xBiMeO3-based ceramics family exhibit distinctive dipole-glass-like relaxor behavior. They demonstrate ultra-wide dielectric stability and exceptionally high critical breakdown field strength, alongside a nearly pseudo-cubic average crystal structure and consistent electric properties across a wide range of x values. However, the mechanisms behind these excellent properties are not clearly understood so far.

    In this thesis, a series of pseudo-cubic 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3-based ceramics were synthesized using solid oxide state reaction techniques. These ceramics display re-entrant dipole-glass-like relaxor behavior and excellent thermal stability of dielectric permittivity above Tm.

    The low-temperature regime of the relaxor behavior of 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3-based ceramics was analyzed using a Vogel-Fulcher law, a new glass model, and a phenomenological statistical model. Characteristics of their dipole-glass-like relaxor nature was further elucidated through polarization-electric field (P-E) loops. Mid-temperature diffuse phase transition (DPT) and high-temperature local phase transitions were described using phenomenological statistical model and isothermal electrical modulus analyses. Additionally, dielectric anomalies in these ceramics were studied through universal dielectric response methods, providing insights into high-temperature phase transitions and defect behaviors. Furthermore, impedance spectrum analysis was used to observe and reveal the correlations between defect types and oxygen partial pressure (PO2) in the 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3-based ceramics. The obtained findings offer novel perspectives on defect behavior and the modification of A and/or B-site cations influencing re-entrant relaxor behavior.