Estudo e determinação de relações estrutura-propriedades do composto TbMnO3

• Ano de defesa: 2013
• Autor(a) principal: Dias, Gustavo Sanguino
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Estadual de Maringá; Brasil; UEM; Maringá, PR; Programa de Pós-Graduação em Física
• Palavras-chave em Português: Materiais multiferróicos; Magnetoelétricos; Manganita de térbio; Brasil.; Ciências Exatas e da Terra; Física
• Link de acesso: http://repositorio.uem.br:8080/jspui/handle/1/2624

In this work, policrystalline TbMnO3 samples, processed by high-energy ball milling, were synthesized in three distinct atmospheres: Argon, Air and Oxygen, for understanding the structure- properties correlations in these materials and the influence of synthesis atmosphere on their physical properties. High-resolution X-ray and neutron diffraction studies revealed the contraction of TbMnO3 unit cell, mainly along the orthorhombic b-axis, for samples synthesized in Air and Oxygen. However, no changes of the Mn valence were observed in the X-ray absorption spectroscopy analyzes. The Neutron powder diffraction studies showed that the Mn sublattice of all TbMnO3 samples exhibit a sinusoidal antiferromagnetic behavior in the antiferromagnetic-paraelectric phase, below 41 K, and a cycloidal noncollinear phase below 27 K, with a propagation direction along the b-axis. As the magnetic ordering of TbMnO3 is governed by the competition between ferromagnetic nearest-neighborhood and antiferromagnetic nextnearest-neighborhood superexchange interactions of Mn ions, the contraction of TbMnO3 unit cell along the b-axis favors the antiferromagnetic near-next- eighborhood superexchange interaction leading to a decrease of the magnetic response for TbMnO3 samples synthesized in Oxygen and Air. This contraction also promotes the reduction of the energy gap between valence and conduction bands, resulting in higher dielectric losses and smaller dielectric constants for Oxygen and Air synthesized samples in comparison to the Argon synthesized one. Dielectric analyzes also revealed the presence of relaxation processes related to the hoopping of charge carriers in grain and grain boundaries, which forms space charges that, consequently, results in an apparent giant dielectric response at room temperature.