TEDE Coleção:
https://tedebc.ufma.br/jspui/handle/tede/tede/707
2024-03-28T14:18:12ZCaracterização estrutural, vibracional e térmica de microbastões de AgVO3
https://tedebc.ufma.br/jspui/handle/tede/tede/5152
Título: Caracterização estrutural, vibracional e térmica de microbastões de AgVO3
Autor: MIRANDA, Antonio Werbeson
Primeiro orientador: MOURA, João Victor Barbosa
Abstract: In this work we present a study of the structural and phonon properties of silver vanadates in
the α-AgVO3 and β-AgVO3 structures. The samples were synthesized by the coprecipitation
method and characterized by X-ray Diffraction (XRD), Raman Spectroscopy and Scanning
Electron Microscopy (SEM). The α-AgVO3 and β-AgVO3 crystals have rod morphology with
micrometric diameter. XRD analyzes together with Rietveld refinement confirmed that the α-
AgVO3 sample crystallized in the monoclinic structure of space group C2/c, Z = 8, with the
lattice parameters a = 10.4499(8) Å, b = 9, 9256 (5) Å, c = 5.5260 (4) Å, β = 99.647 (8) °, V =
565.07 (7) Å3
, while the β-AgVO3 sample was obtained in the monoclinic structure of space
group C1/ m1, Z = 8, with the lattice parameters a = 18.1177 (3) Å, b = 3.58232 (8) Å, c =
8.0389 (2) Å, β = 104.437 (1) °, V = 505.27 (2) Å3
. XRD experiments at low temperatures (298
– 12 K) demonstrated thermal stability of the α-AgVO3 and β-AgVO3 phases and uniaxial
negative thermal expansion in the b direction of the β-AgVO3 microcrystals. Raman
Spectroscopy and XRD experiments at high temperatures (298 – 673 K) demonstrate that α-
AgVO3 microrods exhibit two temperature-induced phase transitions at 413 and 513 K during
heating (α → α' → β'), and a transition at 433 K to the β-AgVO3 phase during return to room
temperature (β' → β). The β-AgVO3 microrods show a structural transition from the monoclinic
phase to a triclinic phase at 473 K (β → β’). The temperature-induced structural modifications
in the α-AgVO3 and β-AgVO3 phases, as well as the uniaxial negative thermal expansion in the
β-AgVO3 phase are not yet demonstrated in the literature.
Instituição: Universidade Federal do Maranhão
Tipo do documento: Dissertação2023-10-11T00:00:00ZEstudo de plasmas magnetizados na eletrodinâmica de Maxwell-Carroll-Field-Jackiw
https://tedebc.ufma.br/jspui/handle/tede/tede/5147
Título: Estudo de plasmas magnetizados na eletrodinâmica de Maxwell-Carroll-Field-Jackiw
Autor: RIBEIRO, Filipe dos Santos
Primeiro orientador: FERREIRA JUNIOR, Manoel Messias
Abstract: The present work addresses, in a simpli ed way, Appleton's model for magnetized plas mas in the context of the usual Maxwell theory and Maxwell-Carroll-Field-Jackiw (MCFJ)
electrodynamics, endowed with a xed 4-vector of Lorentz symmetry violation. We begin by
reviewing the essential aspects of electromagnetic (EM) wave propagation in plasmas, analy zing the scattering relations, refractive index, propagation modes, and the birefringence e ect.
In the sequel, we revisit some basic aspects of Carroll, Field, and Jackiw's electrodynamics,
such as the derivation of the modi ed Maxwell equations and extended scattering relations,
which leads to birefringence in vacuum. Finally, we study Appleton's model in the context of
MCFJ electrodynamics in order to verify the e ects of the CPT- odd term on the propaga ting modes. Using the same procedure, we nd the relations of scattering, refractive index,
propagating modes, and the birefringence e ect. We highlight how the CFJ term alters the
propagation indices and acts on the propagating modes.
Instituição: Universidade Federal do Maranhão
Tipo do documento: Dissertação2021-07-17T00:00:00ZGrafeno interagindo com agrotóxicos: um estudo DFT
https://tedebc.ufma.br/jspui/handle/tede/tede/5056
Título: Grafeno interagindo com agrotóxicos: um estudo DFT
Autor: OLIVEIRA, Andreik Pereira de
Primeiro orientador: GUERINI, Silvete Coradi
Abstract: Pesticides are widely used around the word, especially in less developed contries. These
products, whose objective is to eliminate insects in plantations, infiltrating the soil,
groundwater and the rainwater, which, wen flowing therough the plantations, transport the
pesticides to the rivers, contaminating the waters and aquatic beings. So, is necessary to
detect and remove these toxic substances from the environment. In this work we analyze
the interaction of acephate and glyphosate pesticides with graphene through firts prınciples
calculations, based on the density functional theory, implemented in the Siesta computer
program. It was observed through the binding energy that both acephate and glyphosate
interact with graphene through a physical process in all configurations considered for
analysis. Thus, we propose that graphene is a possible candidate to be used as a filter
to remove the pesticides acephate and glyphosate from the aquatic environment due to
physical interaction.
Instituição: Universidade Federal do Maranhão
Tipo do documento: Dissertação2023-08-31T00:00:00ZEstudo do espectro de Fônons das Perovskitas A2NiB''O6 (A = Sr, Ba; B'' = W, Mo) em função da temperatura
https://tedebc.ufma.br/jspui/handle/tede/tede/4824
Título: Estudo do espectro de Fônons das Perovskitas A2NiB''O6 (A = Sr, Ba; B'' = W, Mo) em função da temperatura
Autor: CORREA, Adriano
Primeiro orientador: SANTOS, Clenilton Costa dos
Abstract: In recent years, the scientific community dedicated to the study in the field of
condensed matter physics has been dedicated to the study of materials of the perovskite
oxide type due to its recognized technological potential. The study of its structural and
vibrational properties have been made by several techniques, such as X-ray Diffraction
and Neutrons and Raman and Infrared spectroscopies, which are very sensitive to the
structural changes of these materials. This work presents a study of the behavior of the
phonons as a function of temperature, in the range of 10 K to 300 K, of the double
perovskites A2NiB
′′O6 (A = Sr, Ba and B
′′ = W, Nb), by means of Raman spectroscopy
technique. It is known that, at room temperature, Strontium-containing compounds
crystallize into a tetragonal structure with I4/m space group and those containing Barium
crystallize into a cubic structure with space group Fm3̅m. Based on this, the Raman
spectra at room temperature were interpreted by means of the factor group analysis in
terms of the respective space groups, where for the first time the unfolding of the doubly
(Eg) and triple (T2g) degenerated phonons for the tetragonal structure, which presents
slight distortion with respect to the cubic one. The Raman spectra as a function of
temperature presented strong evidence of spin-phonon coupling when analyzed in the
temperature range in which the magnetic order of these perovskites occurs (T = 70 K for
Ba2NiWO6, T = 50 K for Ba2NiMoO6, T = 59 K for Sr2NiWO6 and T = 81 K for
Sr2NiMoO6).
Instituição: Universidade Federal do Maranhão
Tipo do documento: Dissertação2018-04-23T00:00:00Z