Banca de QUALIFICAÇÃO: FELIX CHIMEZIE UDECHUKWU

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : FELIX CHIMEZIE UDECHUKWU
Data: 08/10/2026
HORA: 14:00
LOCAL: Santo André
TÍTULO:

DEVELOPMENT OF NEW LEAD-FREE ELECTROSTRICTIVE MATERIALS AND DEVICES

PÁGINAS: 125
RESUMO:

The development of environmentally friendly lead-free electroactive ceramics has stimulated considerable interest in defect-engineered oxide systems for advanced electromechanical applications. This study investigates the processing–structure–property relationships of the CeO₂–HfO₂ binary system, with particular emphasis on conventionally synthesized Ce₀.₅Hf₀.₅O₂ ceramics. An initial compositional investigation was conducted to evaluate the influence of HfO₂ concentration on densification, phase evolution, thermal behaviour, and electrical properties, providing the basis for selecting the equimolar composition for detailed study. Conventionally synthesized Ce₀.₅Hf₀.₅O₂ ceramics were subsequently investigated as a function of sintering temperature, while mechanochemical processing was explored as an alternative synthesis route. Structural, microstructural, thermal, electrical, and electromechanical properties were evaluated using dilatometry, X-ray diffraction with Rietveld refinement, scanning electron microscopy, Raman spectroscopy, thermogravimetric and differential scanning calorimetric analyses, impedance spectroscopy, X-ray absorption spectroscopy, and electrostriction measurements.

The results demonstrate that sintering at 1650 °C is the critical processing condition for stabilizing the orthorhombic HfO₂ phase in the investigated Ce₀.₅Hf₀.₅O₂ and Ce₀.₆Hf₀.₄O₂ ceramics. In contrast, the corresponding samples sintered at 1500 °C did not exhibit the orthorhombic phase, regardless of whether they were prepared by the conventional or mechanochemical route. For the conventionally synthesized Ce₀.₅Hf₀.₅O₂ ceramics, increasing the sintering temperature promoted improved densification, grain growth, and dielectric performance. Despite the pronounced microstructural differences observed by scanning electron microscopy, the electrical conduction mechanism remained essentially unchanged, with activation energies of 0.80 and 0.82 eV for the samples sintered at 1500 °C and 1650 °C, respectively. Most significantly, the ceramic sintered at 1650 °C exhibited giant electrostriction, achieving a longitudinal electrostriction coefficient (M₃₃) of approximately 1.3 × 10⁻¹⁷ m²V⁻², compared with approximately 1.0 × 10⁻¹⁷ m²V⁻² for the ceramic sintered at 1500 °C. These findings demonstrate the decisive role of sintering temperature in controlling phase evolution and electromechanical performance, and establish Ce₀.₅Hf₀.₅O₂ as a promising lead-free electroactive ceramic for future electromechanical applications.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1545738 - MARCIA TSUYAMA ESCOTE
Membro Titular - Examinador(a) Interno ao Programa - 1552290 - ANDRE SANTAROSA FERLAUTO
Membro Titular - Examinador(a) Externo ao Programa - 2123676 - OLAVO LUPPI SILVA
Membro Titular - Examinador(a) Externo à Instituição - REGINALDO MUCCILLO - IPEN
Membro Suplente - Examinador(a) Externo ao Programa - 2604128 - ALEXANDRE JOSE DE CASTRO LANFREDI
Membro Suplente - Examinador(a) Externo à Instituição - Larissa da Silva Marques - UFABC
Membro Suplente - Examinador(a) Externo à Instituição - FÁBIO CORAL FONSECA - IPEN
Membro Suplente - Examinador(a) Externo à Instituição - MANUEL LENTE - UNIFESP