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Synthesis, Characterizations and applications of oxides materials based on CaCu3Ti4O12

Abstract : Perovskite oxides exhibit a large variety of properties because of their structures and chemical compositions. Well known properties of the perovskite oxides are Ferroelectricity in BaTiO3-based oxides and superconductivity in YBa2Cu3O7. The major limit of these compounds is their phase transitions at high temperature, which lead to modify the perovskite properties. CaCu3Ti4O12 (CCTO) exhibit a cubic structure stable at high temperature, it is a double-perovskite (ABO3). CCTO was known as high dielectric material, and can play a key role in photoelectrochemical activity due to its structure. In addition, CCTO can occur a phase transition into the antiferromagnetically ordered phase below Neel temperature TN = 25 K. On the other hand, 2D nanomaterials including graphene oxide (GO) and hexagonal boron nitrides (h-BN) were widely used due their exceptional properties.The aim of this thesis is to investigate the photoelectrochemical, dielectric, and magnetic properties of CCTO based composites. Composites made of CCTO/GO and CCTO/h-BN ceramics were fabricated by solid-state reaction. With the addition of 2D nanosheets materials, the photoelectrochemical performance is enhanced by increasing the generation of photocurrent. CCTO with 3%wt of h-BN showed the insertion of bore (B) and nitrogen (N) into CCTO lattice, leading to Ti-B-O, Ti-N-O bonds and oxygen vacancies on the surface which reduce the bang gap energy and increase the density of generated photocurrent. With 3% of GO, Ti4+ and Cu2+ were reduced to active species Ti3+ and Cu+ respectively and oxygen vacancies were generated at the surface for charge neutralization, leading to generate photocurrent density 50% higher than pure phase of CCTO. In order to investigate 2D nanomaterials effects on magnetic properties of composites, CCTO with 6%wt of nanosheets was prepared and have shown no significant changes in Neel temperature. Finally in the last section, all composites were surface polished to investigate their dielectric properties, measurements showed a low permittivity in comparison to the literature. In conclusion, this work has shown that 2D nanosheets materials incorporation does not affect dielectric and magnetic properties, but enhance strongly the photoelectrochemical behavior of CCTO
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Sara Kawrani. Synthesis, Characterizations and applications of oxides materials based on CaCu3Ti4O12. Other. Université Montpellier, 2019. English. ⟨NNT : 2019MONTS085⟩. ⟨tel-02492225⟩

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