https://tedebc.ufma.br/jspui/handle/tede/706 Mon, 25 May 2026 01:50:04 GMT 2026-05-25T01:50:04Z https://tedebc.ufma.br/jspui/handle/tede/7000 Título: Propriedades estruturais, vibracionais e elétricas das manganitas ortorrômbica eumno3 e hexagonal ErMnO3 Autor: CORREA, Adriano Primeiro orientador: SANTOS, Clenilton Costa dos Abstract: We investigated the structural, magnetic and vibrational properties of orthorhombic EuMnO3 and hexagonal ErMnO3 manganites using X-Ray Diffraction (XRD), Magnetometry, Raman spectroscopy and Dielectric spectroscopy. The structural and vibrational data obtained respectively via X-ray and Raman diffraction are consistent with the Pnma space group orthorhombic symmetries (D2h 16-62) and the P63cm space group hexagonal symmetries (C6υ 3-185)) for the EuMnO3 and ErMnO3 manganites, respectively. X-ray diffraction data as a function of temperature for both manganites show that there are deviations in the monatomic behavior of both lattice parameters and interatomic distances, unprecedented information for both manganites, since structural data as a function of temperature are scarce for these manganites, which allowed us to analyze in more detail the cause of the strong renormalizations of phonon frequencies and evidence of isostructural transitions. In addition, our XRD results for the EuMnO3 manganite give indications of the orbital ordering of the lattice associated with the Jahn-Teller distortion and we also observed, from the structural data, behaviors consistent with the magnetic ordering of the Mn spins in the ac plane, a result that is very interesting since the literature reports difficulty in obtaining the orientation of the spins for EuMnO3. Regarding the ErMnO3 manganite, we observed evidence of the participation of the Mn3+(site 6c) and Er3+(site 4b) spin networks, contrary to what is reported for the hexagonal manganites ReMnO3 (Re = Y, Dy, Ho, Tm, Yb and Lu) that indicate only the participation of the spin network of Mn3+ (site 6c) for the magnetic symmetry. In addition, we observed evidence of the occurrence of isostructural transitions involving the Er3+ spin network occurring from the Γ2Er configuration to the Γ4Er. The dielectric measurements data for the polycrystalline ErMnO3 manganite allowed us to investigate in more detail the contributions of grains and grain boundaries to the electrical conductivity, important results since the few existing results in the literature are concentrated in monocrystalline samples. In addition, the dielectric measurements showed anomalies in the dielectric constant in the vicinity of the magnetic region, these anomalies, together with magnetometry results, suggest the existence of magnetoelectric coupling for ErMnO3. Finally, we show evidence of a coupling between multi-order parameters and their interaction with the magnetoelectric effect in h-ErMnO3. A high magnetostriction response is evidenced by the Einstein-Grüneisen model. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese Fri, 12 Jul 2024 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/7000 2024-07-12T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6868 Título: Determinação da estrutura cristalina do novo complexo de L-Glutamina com Ni(II): um estudo de difração de raios X em policristais auxiliado por análise térmica, vibracional e cálculos DFT Autor: OLIVEIRA, Wesley Kardex Cordeiro de Primeiro orientador: MENEZES, Alan Silva de Abstract: In this work, the determination of the crystal structure of the L-glutamine-nickel complex through X-ray diffraction in polycrystals was carried out and aided by thermal and vibrational analysis and DFT calculations. This material was synthesized in the proportion of 2 mols of L-glutamine and 1 mol of nickel, which grew in the form of polycrystalline spheres. These spheres were ground and subjected to X-ray diffraction measurements in polycrystals. After a search at the Cambridge Crystallographic Data Center (CCDC) for materials that had a crystal structure that matched the diffraction pattern of the complex studied in this work, it was found that the available X-ray diffraction patterns did not match the pattern of the complex. glutamine with nickel. Therefore, a new material had been obtained and therefore its crystal structure had to be determined. From the thermogravimetric analysis, a loss of mass around 160 ◦C was observed, equivalent to the mass of two water molecules, which were coordinated to the metal. Thus, it was considered that the chemical formula of this new complex is: Ni(L-glutamine)2(H2O)2. DFT calculations were performed with the aim of generating an initial molecule to resolve the structure of this crystal. Initially, the analysis of five molecules of the complex was established, arranged with two molecules of glutamine and water linked to the nickel atom. These structures were optimized with the hybrid functional B3LYP with the base function def2-tzvp for the nickel atom and 6-311++G(d,p) for the other atoms, and relaxed scan calculations were performed. in order to build the potential energy surfaces, and identify the most stable structure. With the measurement of X-ray diffraction in polycrystals and with the possible configurations of the optimized molecules, the resolution of the crystal structure Ni(L-glutamine)2(H2O)2 was performed using the Simulated Annealing method. This compound crystallized in a triclinic system with space group P-1, with unit cell parameters a = 5.1308(2) Å, b = 10.6038(9) Å, c = 14.2084(14) Å, α = 104.325 ◦ , β = 96.652 ◦ , γ = 91.433 ◦ and V = 742.79(11) Å 3 . The crystal structure of Ni(L-glutamine)2(H2O)2 consists of two molecules per unit cell (Z = 2), accommodating one molecule in the asymmetric unit (Z’ = 1). The Rietveld method was used to refine the crystal structure and the fit quality indicators were: Rp = 3.53 %, Rwp = 4.77 % and the RBragg = 1.07 %. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação Fri, 13 Aug 2021 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/6868 2021-08-13T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6845 Título: Decaimento de fótons no modelo padrão estendido Autor: Ribeiro Júnior, Marcos Cezar Rios Primeiro orientador: SCHRECK,   Marco Abstract: The discovery of Lorentz symmetry was one of the great advances in modern physics. This symmetry has been increasingly confirmed by various experiments over the past few decades. Thus, a search for small deviations from this symmetry is a window to search for a new physics. The present work is dedicated to photon decay, in the context of the Standard-Model Extension (SME). To develop this subject matter, we initially carried out a literature survey on the Lorentz noninvariant extension of the Standard Model, the well-known SME. Next, we present the characteristics of the photon sector of the SME, such as the Lagrangian, the equation of motion and its solutions, as well as the conservation laws. Later, we discuss photon decay as a consequence of a violation of Lorentz symmetry. We analyze photon decay for a particular type of violation, known as isotropic. Such a violation is obtained from the CPT-even sector of the SME. Furthermore, we discuss some classical and quantum aspects of the isotropic sector of the modified electromagnetic theory and obtain a series of results related to the photon decay process. The fact that photon decay has not been observed in any experiment allows us to set limits on the isotropic coefficient. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação Fri, 07 Aug 2026 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/6845 2026-08-07T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6786 Título: Espalhamento quântico não relativístico no espaço tempo de uma corda cósmica Autor: SOARES, José do Nascimento Linhares Primeiro orientador: SILVA, Edilberto Oliveira Abstract: In this work, we investigate nonrelativistic quantum scattering by a Coulomb potential in the spacetime of a cosmic string. We begin by reviewing the foundations of nonrelativistic quantum mechanics, with emphasis on the Schr¨odinger equation and its essential properties. We then develop the theory of quantum scattering, specializing the formalism to the Coulomb potential. The cosmic string is described by the line element ds2 = −dt2 +dr2 +r2dθ2 +α2r2sin2θdφ2, within which we formulate the Schr¨odinger equation and explicitly solve the problem for scat tering states. From these solutions, we determine the phase shift, the scattering amplitude, and the cross section, highlighting the modifications introduced by the topological defect. Mo reover, we show that the energy spectrum of bound states can be obtained from the poles of the scattering matrix, yielding energy levels corrected by the geometric parameter α. The results reveal that the topology associated with the cosmic string directly influences quantum observables, manifesting itself both in the asymptotic behavior of the scattered waves and in the geometric splitting of the energy levels of the hydrogen atom. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação Mon, 16 Mar 2020 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/6786 2020-03-16T00:00:00Z