Phonon properties of AB (Bernal) stacked bilayer graphene (BLG) with various types of defects have been investigated theoretically. Forced Vibrational (FV) method has been employed to compute the phonon modes of disordered BLG. A downward linear shift of E2g mode frequencies has been observed with an increasing amount of defect concentration. Moreover, two identical E2g peaks have been observed in PDOS of the bilayer system where the individual layer contains 12C and 13C atoms respectively. From computed typical mode patterns of in-plane K-point optical mode phonons, it has been noticed that phonons become strongly localized around a few nanometers area at the presence of defects and localized modes increase with the increasing amount of defect concentration. The edge effect on the localized phonon modes has also been discussed for bilayer armchair graphene nanoribbons (BiAGNRs). The impact of defects on the phonon conduction properties has also been studied for BiAGNRs. My investigated results can be convenient to study the thermal conductivity and electron-phonon interaction of bilayer graphene-based nanodevices and to interpret the Raman and infrared spectra of disordered system.

On account of the high temperatures and pressures experienced by energetic materials during deflagration and detonation, it is important to know not only the physical properties of these materials at ambient temperatures and pressures, but also to understand how their structure and properties are affected by extreme conditions. Combined computational and experimental investigations of the effects of high pressures on the structure and properties of several energetic materials are described herein. A comparison of the performances of different pseudopotentials and density functional theory (DFT) dispersion correction schemes in calculating crystal geometries and vibrational frequencies of crystalline ammonium perchlorate at high pressure is described. The results highlight the fact that care must be taken when choosing pseudopotentials for high-pressure studies. A comprehensive comparison of calculated vibrational modes (including symmetry) with experiment has been performed, with the frequencies of all internal modes predicted to lie within 5% of experimental values. This study established that no significant improvements in the calculation of crystal geometries of ammonium perchlorate are obtained by employing DFT-D corrections. The enthalpy of fusion (ΔHfus) of the highly metastable β-form of RDX (cyclotrimethylenetrinitramine) was determined to be 12.63 ± 0.28 kJ mol-1. DFT-D calculations of the lattice energies of the α- and β-forms of RDX are described. Furthermore, the response of the lattice parameters and unit-cell volumes to pressure for the α-, γ- and ε-forms of RDX calculated using DFT-D are in very good agreement with experimental data. Phonon calculations provide good agreement with vibrational frequencies obtained from Raman spectroscopy, and a predicted inelastic neutron scattering (INS) spectrum of α-RDX shows excellent agreement with experimental INS data recorded as part of this study. The results of the high-pressure phonon calculations have been used to show that the heat capacities of the α-, γ- and ε- forms of RDX are only weakly affected by pressure. DFT-D calculations have been utilised to describe accurately the structure and properties of both β-HMX (Cyclotetramethylenetetranitramine) and α-FOX-7 (1,1-Diamino-2,2-dinitroethylene) as a function of pressure. This work presents data for the experimental hydrostatic compression of both deuterated β-HMX and α-FOX-7 performed using neutron powder diffraction at the ISIS Neutron and Muon facility, in addition to experimental determinations of the INS spectra of both β-HMX and α-FOX-7. The DFT-D hydrostatic compression studies for both materials reproduce the experimental compression trends. Furthermore, the calculated vibrational properties as a function of pressure were in very good agreement with available experimental data. The results of the phonon calculations were then used to predict the effect of pressure on the heat capacities of β-HMX and α-FOX-7. These predictions suggest a very weak pressure dependence of heat capacities (approximately -1 J K-1 mol-1 GPa-1) for these materials. This work demonstrates that the DFT-D model performs extremely well over a range of conditions, and is able to describe accurately intramolecular and intermolecular interactions, and thus the structure and properties of organic molecular nitramine crystals. The computational model was therefore used to predict the high-pressure hydrostatic compression behaviour of a related nitramine, CL-20 (2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane), the results of which highlighted possible discrepancies in the experimental high-pressure X-ray diffraction data recorded for ε-CL-20. This prompted a high-pressure neutron powder diffraction study, which showed good agreement with the computational results, thereby highlighting radiation damage in the X-ray experiments.

Research on two-dimensional (2D) materials currently occupies a sizeable fraction of the materials science community, which has led to the development of a comprehensive body of knowledge on such layered structures. However, the goal of this thesis is to deepen the understanding of the comparatively unknown heterostructures composed of different stacked layers. First, we utilise linear-scaling density functional theory (LS-DFT) to simulate intricate interfaces between the most promising layered materials, such as transition metal dichalcogenides (TMDC) or black phosphorus (BP) and hexagonal boron nitride (hBN). We show that hBN can protect BP from external influences, while also preventing the band-gap reduction in BP stacks, and enabling the use of BP heterostructures as tunnelling field effect transistors. Moreover, our simulations of the electronic structure of TMDC interfaces have reproduced photoemission spectroscopy observations, and have also provided an explanation for the coexistence of commensurate and incommensurate phases within the same crystal. Secondly, we have developed new functionality to be used in the future study of 2D heterostructures, in the form of a linear-response phonon formalism for LS-DFT. As part of its implementation, we have solved multiple implementation and theoretical issues through the use of novel algorithms.

PEREIRA, José Enedilton Medeiros. Espectroscopia vibracional em cristais do ácido trans-cinâmico complexado com európio sob condições extremas. 2014. 90 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-09-12T19:42:18Z No. of bitstreams: 1 2014_dis_jempereira.pdf: 4086204 bytes, checksum: f746c208810c91b5b87b4ef1b2f4de4a (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-09-12T19:50:42Z (GMT) No. of bitstreams: 1 2014_dis_jempereira.pdf: 4086204 bytes, checksum: f746c208810c91b5b87b4ef1b2f4de4a (MD5) / Made available in DSpace on 2014-09-12T19:50:42Z (GMT). No. of bitstreams: 1 2014_dis_jempereira.pdf: 4086204 bytes, checksum: f746c208810c91b5b87b4ef1b2f4de4a (MD5) Previous issue date: 2014 / This work is focused on characterization of a polycrystalline sample of the coordination compound with ions Eu3+ using as a binder the trans-cinnamic acid , [Eu(cin)3]. The interest in coordination with lanthanide compounds is due to their large technological applications. The process of luminescence of coordination compounds containing lanthanide, also called antenna effect, has a main objective the use of new ligands with various applications, both in increasing the efficiency of energy receptors in the ultraviolet region and the development of biomarkers. In this work, to characterize the polycrystalline material, Raman spectroscopy was used to determine the vibrational behavior of the material at ambient temperature and pressure. It was also shown the behavior of the compound at low temperatures, in which variations in various vibrational modes were observed, indicating thus the occurrence of phase transition. Using a diamond anvil cell the material was studied by high hydrostatic pressure Raman spectroscopy. The purpose of this methodology was to map possible phase transitions and discover the occurrence of possible polymorphism. However, until the pressure reached in the experiments - about 5.2 GPa - it was found that the original phase remained stable. A discussion of the luminescence of the sample is also provided in this work. / O presente trabalho está focado na caracterização de uma amostra policristalina do composto de coordenação com íons Eu3+ utilizando como ligante o ácido trans-cinâmico, [Eu(cin)3]. O interesse em compostos de coordenação com lantanídeos deve-se às suas amplas aplicações tecnológicas. O processo de luminescência dos compostos de coordena- ção contendo lantanídeo, também chamado de efeito antena, tem como principal objetivo o uso de novos ligantes com aplicações diversas, tanto no aumento da eficiência de re- ceptores de energia na região do ultravioleta quanto no desenvolvimento de marcadores biológicos. Neste trabalho, para realizar a caracterização do material policristalino, foi utilizada a espectroscopia Raman, a fim de determinar o comportamento vibracional do material à temperatura e pressão ambiente. Também foi verificado o comportamento do composto sob baixas temperaturas, no qual foram observadas variações em vários modos vibracionais, indicando, por conseguinte, a ocorrência de transição de fase. Utilizando uma célula de pressão a extremos de diamante o material foi estudado a altas pressões hidrostáticas através de espectroscopia Raman. O intuito desta metodologia era mapear possíveis transições de fase e descobrir a ocorrência de eventual polimorfismo. Entretanto, até a pressão atingida nos experimentos – cerca de 5,2 GPa – verificou-se que a fase ori- ginal permaneceu estável. Uma discussão sobre a luminescência da amostra também é fornecida neste trabalho.

The major objective of this thesis is to systematically investigate the effect of hexagonal BN (h-BN) islands on electronic and vibrational properties of single wall carbon Nanotubes. All our investigation are based on first principle Density Functional Theory (DFT) calculations. Our study is motivated by interesting metal-semiconductor transition recently found in periodically patterned graphene with h-BN islands. After reproducing the electronic band structure for pristine single wall zigzag carbon nanotubes (which shows metallic or semiconducting properties depending on their chirality), we investigated their electronic band structure in the presence of h-BN islands. The band structure depends not only on the defect concentration, but also on the pattern of the defect atoms. Our results also suggest that, if we start with a metallic /semiconducting mixture of ZSWCNTs, upon h-BN addition, the sample converts to fully semiconducting. This is a promising result for applications of CNTs in molecular electronics. Fundamental understanding of vibrational properties of nano electronics component is equally important in their applications especially in thermal management and thermoelectric applications. Defect engineering is one of the potential approach for tuning nanoelectronic devices for optimal thermal management and thermoelectric devices. In this work, I present a systematic investigation on how the group velocity and frequency of different phonon modes depend on various h-BN defect concentrations and defect patterns in ZSWCNTs. The study was extended to investigate the effect of hexagonal-C defects on the electronic and vibrational properties of zigzag single wall Boron Nitride nanotubes (ZSWBNNTs).

MAIA, José Robson. Estudo da cafeína anidra sob condições extremas através de Espectroscopia Raman. 2010. 82 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2010. / Submitted by francisco lima (admir@ufc.br) on 2014-06-30T17:14:06Z No. of bitstreams: 1 2010_dis_jrmaia.pdf: 2070388 bytes, checksum: 91f8d25cd08ec0e46e3c280ebd10e9d0 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-08-06T17:23:39Z (GMT) No. of bitstreams: 1 2010_dis_jrmaia.pdf: 2070388 bytes, checksum: 91f8d25cd08ec0e46e3c280ebd10e9d0 (MD5) / Made available in DSpace on 2014-08-06T17:23:39Z (GMT). No. of bitstreams: 1 2010_dis_jrmaia.pdf: 2070388 bytes, checksum: 91f8d25cd08ec0e46e3c280ebd10e9d0 (MD5) Previous issue date: 2010 / In this work anidrous cafeine (C8H10N4O2) crystals were investigated through the Raman spectroscopy technique, with change of temperature and pressure, in the spectral region between 30 and 3200 cm-1 In the temperature experiments the thermodynamic parameter changed from 23 and 170 0C. From them it was possible to realize that anidrous cafeine undergoes a structural phase transition at about 140 0C, as pointed by the disappearance of three bands associated to external modes. After sample goes back to room temperature, it is observed that the original Raman spectrum was not recovered, indicating that the transition is not reversible. Thermal analysis experiment confirms the structural phase transition undergone by cafeine. In order to perform high pressure experiments we have used a diamond anvil cell, being possible to arrive to pressures up to 10.6 GPa. In the high pressure Raman experiments it was possible to observe a phase transition at about 1 GPa, as indicated by the appearance of a band at 37 cm-1 as well as a second phase transition between 6.2 and 7.5 GPa. This last phase transition was characterized by the discontinuity in the frequency band of two low energy. In the pressure range 7.3-10.6 GPa, the Raman scattering experiments performed on anidrous cafeine showed indicious of lost of long range order, which was interpreted as a possible amorphization of the sample. / No presente trabalho policristais de cafeína anidra (C8H10N4O2), foram investigados por meio de experimentos de espectroscopia Raman, com variação dos parâmetros termodinâmicos temperatura e pressão, em uma região espectral entre 30 e 3200 cm-1. Nos experimentos de espectroscopia Raman realizados variando a temperatura entre 23 e 170 °C, verificou-se que a cafeína anidra sofreu uma transição de fase estrutural em torno de 140 °C, acompanhada pelo desaparecimento de três dos modos externos. A análise dos espectros Raman obtidos após o retorno a temperatura ambiente revelaram que a cafeína não recupera a fase beta. O experimento de análise térmica confirma a transição de fase estrutural sugerida pelos experimentos de espectroscopia Raman a altas temperaturas. Nos experimentos de altas pressões utilizando-se uma célula de pressão a extremos de diamantes os cristais foram submetidos a pressões de até 10,6 GPa. Em tais experimentos pode-se observar uma transição de fase, em torno de 1 GPa devido ao surgimento de uma banda Raman em aproximadamente 37 cm-1 e uma outra transição em um intervalo de pressão compreendido entre 6,2 e 7,5 GPa, relacionado a uma descontinuidade na freqüência de duas bandas de baixa energia. Para o intervalo de pressão entre 7,3 e 10,6 GPa os experimentos de espectroscopia Raman realizadas sobre policristais de cafeína anidra mostraram fortes indícios de perda da ordem de longo alcance o que foi interpretado como uma possível amorfização da amostra.

GONÇALVES, Ricardo Oliveira. Espalhamento Raman em Policristais de L-alanina deuterados sob pressão. 2008. 78 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2008. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-06-08T19:38:31Z No. of bitstreams: 1 2008_dis_rogoncalves.pdf: 6962166 bytes, checksum: 5422b2af7936494743aae69cbce2e2e3 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-06-08T19:52:47Z (GMT) No. of bitstreams: 1 2008_dis_rogoncalves.pdf: 6962166 bytes, checksum: 5422b2af7936494743aae69cbce2e2e3 (MD5) / Made available in DSpace on 2015-06-08T19:52:47Z (GMT). No. of bitstreams: 1 2008_dis_rogoncalves.pdf: 6962166 bytes, checksum: 5422b2af7936494743aae69cbce2e2e3 (MD5) Previous issue date: 2008 / In this dissertation we present of Raman spectroscopy on deuterated L-alanine crystals under hydrostatic pressure. L-alanine is one of twenty proteic amino acids, and among them it is the simplest chiral one. L-alanine crystallizes in an orthorhombic (D24) structure with four molecules per unit cell, forming a complex network of seven hydrogen bonds. When one applies pressure on an amino acid crystal the distances between molecules are changed and, eventually, the crystal goes to a new structure with different symmetry. In this work we present the Raman spectra of deuterated L-alanine in the 50 - 2500 cm-1 spectral region with pressures changing from 0 to 6 GPa. Beyond the conventional frequency blue shift of almost all modes, we observed frequency discontinuities of both internal and external modes at 1,5 and 4,5 GPa. These discontinuities were interpreted as structural phase transitions undergone by deuterated L-alanine crystal from the orthorhombic to the tetragonal, and from the tetragonal to a monoclinic symmetry, respectively. This suggestion is based on previous results on non - deuterated L-alanine. The behavion of torcional vibration of ND3 was also studied and a comparison with studies on L-alanine, L-threonine and taurine crystals (related with dimensions of hydrogen bonds) is also given. / Nesta Dissertação são apresentados os resultados oriundos do estudo do efeito da aplicação de pressão hidrostática sobre cristais de L-alanina deuterada. A L-alanina é um dos vinte aminoácidos formadores das proteínas, sendo entre os quirais o mais simples deles. A L-alanina cristaliza-se numa estrutura ortorrômbica (D24) com quatro moléculas por célula unitária formando uma complexa rede de sete diferentes ligações de hidrogênio. Quando pressão é aplicada a um cristal de aminoácidos ocorre a aproximação das moléculas com a consequente variação nas distâncias e ângulos das ligações de hidrogênio, eventualmente obrigando a estrutura a ir para uma nova simetria. Investigou-se nesta Dissertação o comportamento dos espectros Raman da L-alanina deuterada na região espectral entre 50 e 2500 cm-1 para pressões variando entre 0 e 6 GPa. Além do usual comportamento do desvio da freqüência de quase todos os modos para altos valores, observou-se também descontinuidades nas freqüências de modos internos e modos externos para valores de pressão em 1,5 e 4,5 GPa. Estas descontinuidades foram interpretadas como sendo consequências de transições de fase estruturais de uma estrutura ortorrômbica para uma estrutura tetragonal e, a seguir, para uma estrutura monoclínica em analogia ao que ocorre com a L-alanina não deuterada. O comportamento do modo de torção da estrutura ND3 também foi estudado e uma analogia do seu comportamento com aqueles observados na L-alanina, na L-treonina e na taurina em termos das dimensões das ligações de hidrogênio também é fornecida.

SILVA, Antônio Neves da. Caracterização de Óxidos Nanoestruturados através de Espectroscopia Raman em condições de pressões elevadas. 2015. 115 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2015. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-06-11T18:16:10Z No. of bitstreams: 1 2015_tese_ansilva.pdf: 10244378 bytes, checksum: f5574341b39d6d68105f6205b730556d (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-06-11T18:25:13Z (GMT) No. of bitstreams: 1 2015_tese_ansilva.pdf: 10244378 bytes, checksum: f5574341b39d6d68105f6205b730556d (MD5) / Made available in DSpace on 2015-06-11T18:25:13Z (GMT). No. of bitstreams: 1 2015_tese_ansilva.pdf: 10244378 bytes, checksum: f5574341b39d6d68105f6205b730556d (MD5) Previous issue date: 2015 / Raman spectroscopy studies has been used to investigate the structural properties of nanocasted oxides, CeO2 (Ce), ZrO2 (Zr), TiO2 (Ti), SnO2 (Sn), MnOx (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) and NiO−Al2O3 (NiAl), obtained from nanocasting technique. The studies were collaborated by Transmission Electron Microscopy (TEM) and Infrared Spectroscopy with Fourier transform (FT-IR) techniques. The results suggested that Ce, Sn and Mn monoxides have structural defects (vacancies) derived from the preparation method of the solids. This result is indeed not common for ordinary oxides. At room pressure Ti anatase is tetragonal belonging to D4h19 (I41/amd) space group and changes for the monoclinic phase at pressures around 14 GPa. With pressure release Ti changes to orthorhombic phase. The sample Mn showed a phase transition at about 17,5 GPa, whose phase is still unknown. For all samples the spectra appear strongly influenced by the particle size, shape and structure of the material, especially in the position value of pression for phase transition. The Ce, Zr and Sn remained stable up to the maximum pressure achieved and Ti and Mn showed phase transition. TEM analysis estimated the average nanoparticle size of 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) and 8 nm (CeAl); and distance between crystallographic planes of d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0,32 nm (CeMn) e d111 = 0,3 nm (CeAl). The nanoparticles sizes for Ce, CeMn and CeAl, obtained from Raman spectroscopy data were 7, 8 and 3 nm, respectively, wich agree well with the results of TEM. The images suggest that all the nanoparticles were distributed over the remaining silica surface. All nanoparticles were agglomerated in some regions, due to the fact that in the silica-based nanocomposites, calcination leads to migration to nucleation sites. The FT-IR spectra indicated the presence of modes related to vibrations of OH bonds in na- nostructures; and the vibrations of Ce-O, Sn-O and Mn-O bonds of Ce, Sn and Mn oxides, respectively. The spectra of sample CeMn showed that the interaction between Mn and Ce can break the structure of the fluorite type and form oxygen vacancies in the Ce structure whereas the CeMn and NiAl high pressure results showed line broadening, decreasing in modes intensity and remained stable until the maximum pressure value reached, 14 and 18 GPa respectively. The stability of CeAl was maintained up to 36 GPa, in contrast with that observed for Ce monoxide, in which a phase transition occurs at about 35 GPa to a structure of PbCl2 orthorhombic (space group D2h16). The introduction of oxide Al2O3 in the structure of CeO2 increases the stability of this structure. The effect of varying laser power incident in nanostructured oxides showed an increase in intensity in all nano oxides spectra with the increasing laser power. Mn oxide, in particular, presented an increase in the modes related to defects due to vacancies generated by OH removing. / Neste trabalho caracteriza-se os óxidos de Cério (Ce), Zircônio (Zr), Titânio (Ti), Estanho (Sn), Manganês (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) e NiO−Al2O3 (NiAl), sintetizados a partir do método da nanomoldagem, por espectroscopia Raman a altas pressões, Microscopia Eletrônica de Transmissão (TEM) e Espectroscopia na região do Infravermelho com transformada de Fourier FT-IR. Os resultados sugerem que os monóxidos Ce, Sn e Mn possuem defeitos estruturais (vacâncias) derivados do método de preparação dos sólidos. Na pressão ambiente Ti anatase é tetragonal pertencendo ao grupo espacial D4h19 (I41/amd) e muda para a fase monoclínica, em pressões em torno de 14 GPa. Ao se realizar a descompressão Ti muda para a fase ortorrômbica. A amostra Mn mostrou uma transição de fase em cerca de 17,5 GPa, cuja fase ainda é desconhecida. Através da análise de TEM, estimou-se o tamanho médio das nanopartículas de 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) e 8 nm (CeAl); e distância entre planos cristalográficos de d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0, 32 nm (CeMn) e d111 = 0,3 nm (CeAl). Os tamanhos médios estimados para o Ce, CeMn e CeAl, através dos dados de espectroscopia Raman foram de 7, 8 e 3 nm respectivamente, em concordância com os resultados de TEM. As micrografias sugerem que todas as nanopartículas estavam distribuídas sobre a superfície da sílica remanescente e todas apresentaram-se aglomeradas em algumas regiões, devido ao fato de que em nanocompostos à base de sílica, a calcinação conduz à migração para sítios de nucleação. Os modos identificados nos espectros FT-IR foram relacionados às vibrações das ligações O-H nas nanoestruturas e às vibrações das ligações Ce-O, Sn-O e Mn-O dos óxidos Ce, Sn e Mn, respectivamente. Os experimentos sob condições de altas pressões do CeMn mostram que a interação entre Mn e Ce pode deformar a estrutura do tipo fluorita e formar vacâncias de oxigênio na rede de Ce. Os óxidos CeMn e NiAl apresentaram alargamento de linha, diminuição na intensidade dos modos e permaneceram estáveis até o valor máximo de pressão alcançado, 14 e 18 GPa respectivamente. Para o sólido CeAl, a estabilidade da fase cúbica é mantida até 36 GPa, fato oposto àquele observado para o monóxido Ce, no qual ocorre uma transição de fase em cerca de 35 GPa para uma estrutura do tipo PbCl2 ortorrômbica (grupo espacial D2h16). Conclui-se que a introdução do óxido Al2O3 na estrutura do CeO2 aumenta a estabilidade dessa estrutura. Os experimentos com a variação da potência mostraram que o aumento na potência está relacionado a um aumento na intensidade dos modos em todos os óxidos. O óxido Mn, em particular, apresentou um aumento nos modos de defeitos devido às vacâncias geradas pela eliminação da água presente, evidenciado pelos modos do grupo OH.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Neste trabalho caracteriza-se os Ãxidos de CÃrio (Ce), ZircÃnio (Zr), TitÃnio (Ti), Estanho (Sn), ManganÃs (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) e NiO−Al2O3 (NiAl), sintetizados a partir do mÃtodo da nanomoldagem, por espectroscopia Raman a altas pressÃes, Microscopia EletrÃnica de TransmissÃo (TEM) e Espectroscopia na regiÃo do Infravermelho com transformada de Fourier FT-IR. Os resultados sugerem que os monÃxidos Ce, Sn e Mn possuem defeitos estruturais (vacÃncias) derivados do mÃtodo de preparaÃÃo dos sÃlidos. Na pressÃo ambiente Ti anatase à tetragonal pertencendo ao grupo espacial D4h19 (I41/amd) e muda para a fase monoclÃnica, em pressÃes em torno de 14 GPa. Ao se realizar a descompressÃo Ti muda para a fase ortorrÃmbica. A amostra Mn mostrou uma transiÃÃo de fase em cerca de 17,5 GPa, cuja fase ainda à desconhecida. AtravÃs da anÃlise de TEM, estimou-se o tamanho mÃdio das nanopartÃculas de 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) e 8 nm (CeAl); e distÃncia entre planos cristalogrÃficos de d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0, 32 nm (CeMn) e d111 = 0,3 nm (CeAl). Os tamanhos mÃdios estimados para o Ce, CeMn e CeAl, atravÃs dos dados de espectroscopia Raman foram de 7, 8 e 3 nm respectivamente, em concordÃncia com os resultados de TEM. As micrografias sugerem que todas as nanopartÃculas estavam distribuÃdas sobre a superfÃcie da sÃlica remanescente e todas apresentaram-se aglomeradas em algumas regiÃes, devido ao fato de que em nanocompostos à base de sÃlica, a calcinaÃÃo conduz à migraÃÃo para sÃtios de nucleaÃÃo. Os modos identificados nos espectros FT-IR foram relacionados Ãs vibraÃÃes das ligaÃÃes O-H nas nanoestruturas e Ãs vibraÃÃes das ligaÃÃes Ce-O, Sn-O e Mn-O dos Ãxidos Ce, Sn e Mn, respectivamente. Os experimentos sob condiÃÃes de altas pressÃes do CeMn mostram que a interaÃÃo entre Mn e Ce pode deformar a estrutura do tipo fluorita e formar vacÃncias de oxigÃnio na rede de Ce. Os Ãxidos CeMn e NiAl apresentaram alargamento de linha, diminuiÃÃo na intensidade dos modos e permaneceram estÃveis atà o valor mÃximo de pressÃo alcanÃado, 14 e 18 GPa respectivamente. Para o sÃlido CeAl, a estabilidade da fase cÃbica à mantida atà 36 GPa, fato oposto Ãquele observado para o monÃxido Ce, no qual ocorre uma transiÃÃo de fase em cerca de 35 GPa para uma estrutura do tipo PbCl2 ortorrÃmbica (grupo espacial D2h16). Conclui-se que a introduÃÃo do Ãxido Al2O3 na estrutura do CeO2 aumenta a estabilidade dessa estrutura. Os experimentos com a variaÃÃo da potÃncia mostraram que o aumento na potÃncia està relacionado a um aumento na intensidade dos modos em todos os Ãxidos. O Ãxido Mn, em particular, apresentou um aumento nos modos de defeitos devido Ãs vacÃncias geradas pela eliminaÃÃo da Ãgua presente, evidenciado pelos modos do grupo OH. / Raman spectroscopy studies has been used to investigate the structural properties of nanocasted oxides, CeO2 (Ce), ZrO2 (Zr), TiO2 (Ti), SnO2 (Sn), MnOx (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) and NiO−Al2O3 (NiAl), obtained from nanocasting technique. The studies were collaborated by Transmission Electron Microscopy (TEM) and Infrared Spectroscopy with Fourier transform (FT-IR) techniques. The results suggested that Ce, Sn and Mn monoxides have structural defects (vacancies) derived from the preparation method of the solids. This result is indeed not common for ordinary oxides. At room pressure Ti anatase is tetragonal belonging to D4h19 (I41/amd) space group and changes for the monoclinic phase at pressures around 14 GPa. With pressure release Ti changes to orthorhombic phase. The sample Mn showed a phase transition at about 17,5 GPa, whose phase is still unknown. For all samples the spectra appear strongly influenced by the particle size, shape and structure of the material, especially in the position value of pression for phase transition. The Ce, Zr and Sn remained stable up to the maximum pressure achieved and Ti and Mn showed phase transition. TEM analysis estimated the average nanoparticle size of 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) and 8 nm (CeAl); and distance between crystallographic planes of d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0,32 nm (CeMn) e d111 = 0,3 nm (CeAl). The nanoparticles sizes for Ce, CeMn and CeAl, obtained from Raman spectroscopy data were 7, 8 and 3 nm, respectively, wich agree well with the results of TEM. The images suggest that all the nanoparticles were distributed over the remaining silica surface. All nanoparticles were agglomerated in some regions, due to the fact that in the silica-based nanocomposites, calcination leads to migration to nucleation sites. The FT-IR spectra indicated the presence of modes related to vibrations of OH bonds in na- nostructures; and the vibrations of Ce-O, Sn-O and Mn-O bonds of Ce, Sn and Mn oxides, respectively. The spectra of sample CeMn showed that the interaction between Mn and Ce can break the structure of the fluorite type and form oxygen vacancies in the Ce structure whereas the CeMn and NiAl high pressure results showed line broadening, decreasing in modes intensity and remained stable until the maximum pressure value reached, 14 and 18 GPa respectively. The stability of CeAl was maintained up to 36 GPa, in contrast with that observed for Ce monoxide, in which a phase transition occurs at about 35 GPa to a structure of PbCl2 orthorhombic (space group D2h16). The introduction of oxide Al2O3 in the structure of CeO2 increases the stability of this structure. The effect of varying laser power incident in nanostructured oxides showed an increase in intensity in all nano oxides spectra with the increasing laser power. Mn oxide, in particular, presented an increase in the modes related to defects due to vacancies generated by OH removing.

The vibrational properties of spruce (Picea abies Karst.) and European beech (Fagus sylvatica L.) were investigated in this study in dependence on the relative humidity (RH). The RH was measured at 20 °C ranging from oven-dried to 85%. For the evaluation of the vibrational properties the dynamic modulus of elasticity E’ and the damping coefficient tan δ were measured at 7 climate steps. The same samples used for the vibrational tests were afterwards mildly thermally modified at 180 °C and measured at the same climate steps. Both wood species were compared and evaluated considering the property changes (E’, tan δ, sorption isotherms and volume swelling) due to the thermal modification. The chosen modification resulted in a marginal change in the vibrational properties of spruce, whereas the properties of beech were clearly changed. The vibrational properties of beech could be improved in the usual RH range (35–85%) due to this thermal modification. For spruce, it was concluded that a mild modification, conducted in this study, is not suitable for improving the vibrational properties. Further conclusions concerning the underlying causes as well as the use in musical instruments were drawn.