Produção e estudo dos defeitos de materiais fotossensíveis com estrutura cristalina do tipo silenita

• Autor(a) principal: Santos, Denise de Jesus
• Data de Publicação: 2014
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/handle/riufs/5317
• topic: Físico-química; Cristalografia; Titanatos; Bismuto; Metais de transição; Terras-raras; Difração; Raios X; Materiais fotossensíveis; Chemistry, Physical and theoretical; Crystallography; Difration; Earths, Rare; Titanates; Transition metals; X-rays; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

Photorefractive BTO presents useful properties for applications such as real-time holography, coherent light amplification and optical information processing, among others. The performance strongly depends on the defects induced by impurities, which can act as charge donors or acceptors. Defects can also be created by doping so that the properties can be adjusted to the desired application. Since ceramic reproduce well the single crystal properties and have advantages such as the simplicity and low cost of processing, they become suitable for the study of the relationship between properties and defects in this material. The subject of this work was the production and characterization of bismuth titanate ceramics ( Bi12TiO20 - BTO) pure and doped with transition metals and rare earths. The study was focused on the point defects related to the site occupancy of the dopant in the BTO matrix, as well as on the valence of the dopant and possible charge compensation mechanisms associated with the defects. In this work, BTO ceramics were produced by solid state synthesis with calcination at 700º C/6h and sintering at 800º C/3h. The characterization techniques employed were Xray Diffraction (XRD), X-ray absorption spectroscopy (XAS), Scanning Electron Microscopy (SEM) and Impedance Spectroscopy (IS). Undoped and Dy , Er , Eu, Cr and Mn-doped BTO ceramic powders were produced, as well as ceramic bodies undoped and doped with Dy, Cr and Mn. All samples presented single phase Bi12TiO20. The XAS analysis revealed the presence of T4+ and metallic Ti in BTO, a result that adds detail to the model for the formation of intrinsic defects in this material. Transition metals Cr and Mn presented oxidation states 6+ and 4+, respectively, when inserted into the BTO matrix, while the other elements present valence 3+. Concerning the site occupancy, it was determined that the Dy tends to occupy the Bi3+ site, while Er, Eu, Mn and Cr tend to occupy the Ti4+ site. Impedance measurements showed that none of the doped samples had higher dark conductivity than pure sample. For the samples doped with Mn and Dy, which tend to occupy the Ti and Bi sites, respectively, the charge transport mechanisms are exactly the same as those verified in pure sample. For the Cr-doped sample, the Ti substitution occurs with a charge compensation mechanism that possibly give rise to new defects in the material.