TEDE Communidade:https://tedebc.ufma.br/jspui/handle/tede/7062026-08-10T02:08:41Z2026-08-10T02:08:41ZPropriedades estruturais, eletrônicas e energéticas de pesticidas interagindo com nanotubos de nitreto de gálioLIRA JUNIOR, Paulo Brito Oliveirahttps://tedebc.ufma.br/jspui/handle/tede/71462026-08-06T15:09:06Z2024-09-26T00:00:00ZTítulo: Propriedades estruturais, eletrônicas e energéticas de pesticidas interagindo com nanotubos de nitreto de gálio
Autor: LIRA JUNIOR, Paulo Brito Oliveira
Primeiro orientador: GUERINI, Silvete Coradi
Abstract: The structural, electronic and energetic properties of single-walled (10, 0) GaN nanotube
(GaNNT) interacting with the pesticides acephate and glyphosate, in different configurations,
were investigated through first-principles calculations based on density functional theory
( DFT) broke in the SIESTA computer program, to verify the use of GaNNT as a filter
or sensor for pesticides. The calculation results indicate that acephate and glyphosate
can be adsorbed on the GaNNT wall through electrostatic interaction. The results also
show that acephate and glyphosate change the properties of the nanotube when they
interact with it. The band structure for GaNNT was pure modified with the adsorption of
acephate and glyphosate by the appearance of localized levels, as well as the reduction of
the energy gap. The binding energy shows that the interaction of acephate and glyphosate
with GaNNT occurs via a chemical process. Our results also indicate that GaNNT is a
promising material for detecting and removing pesticides from the environment.
Instituição: Universidade Federal do Maranhão
Tipo do documento: Dissertação2024-09-26T00:00:00ZPropriedades estruturais, vibracionais e elétricas das manganitas ortorrômbica eumno3 e hexagonal ErMnO3CORREA, Adrianohttps://tedebc.ufma.br/jspui/handle/tede/70002026-05-22T03:07:47Z2024-07-12T00:00:00ZTítulo: 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: Tese2024-07-12T00:00:00ZDeterminação 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 DFTOLIVEIRA, Wesley Kardex Cordeiro dehttps://tedebc.ufma.br/jspui/handle/tede/68682026-03-26T11:44:12Z2021-08-13T00:00:00ZTítulo: 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: Dissertação2021-08-13T00:00:00ZDecaimento de fótons no modelo padrão estendidoRibeiro Júnior, Marcos Cezar Rioshttps://tedebc.ufma.br/jspui/handle/tede/68452026-03-16T18:37:01Z2026-08-07T00:00:00ZTítulo: 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: Dissertação2026-08-07T00:00:00Z