Magnetism and multiferroic properties at MnTiO3 surfaces: A DFT study

The present study illustrates how density functional theory calculations can rationalize the surface structure and magnetism for the low-index (1 1 0), (1 0 1), (1 0 0), (0 0 1), (1 1 1), and (0 1 2) surfaces of MnTiO3. A simple procedure, without surface reconstructions or chemical adsorptions in which the stability, magnetism and the morphological transformations is presented in detail to clarify the control of their multiferroic nature. The surface stability was found to be controlled by the octahedral [MnO6] and [TiO6] clusters formed by the Mn2+ and Ti4+ cations - i.e., their local coordination at the surfaces, respectively- with nonpolar (1 1 0) being the most stable. Enhanced superficial magnetism was found for (0 1 2), (0 0 1), and (1 1 1) surfaces in agreement with the more undercoordinated [TiOn]′ and [MnOn]• complex clusters at the surface plane. Our calculation suggests the existence of magnetic [TiOn]′ species for unstable (0 0 1) and (1 1 1) surfaces, explained by the unusual crystal-field associated with the surface environment. The crystal morphology has been predicted to determine the most likely terminations to be present as well as the intrinsic magnetization density associated with morphologies. Moreover, the (0 0 1) surface plane plays a key role in the enhancement of the magnetic properties for shape-oriented MnTiO3 nanoparticles, suggesting a superior magnetoelectric coupling due to the presence of uncompensated spins and polar distortions perpendicular to the surface plane

A DFT investigation of the role of oxygen vacancies on the structural, electronic and magnetic properties of ATiO3 (A = Mn, Fe, Ni) multiferroic materials

In order to achieve deep insight into the multiferroic behavior and electronic properties of intrinsic oxygen vacancies in ATiO3 (A = Mn, Fe, Ni), first-principles calculations based on hybrid density functional theory were carried out for bulk and non-polar (110) surface models. We found that the formation of an oxygen vacancy is accompanied by structural and electronic disorders in the constituent clusters of [TiO6] and [AO6] in ATiO3, that become [TiO5] and [AO5], respectively. This perturbation contributes to the generation of intermediary energy levels in the band gap region, thus narrowing the required excitation energy. In addition, the remaining electrons are mainly trapped in the empty 3d orbitals of the Ti cations neighboring the oxygen vacancy, generating [TiO5] 0 (3d1 ) that mediates an antiferromagnetic to ferromagnetic transition in MnTiO3 and FeTiO3 materials. In particular, MnTiO3 surfaces show exposed [TiO4] 0 species that are responsible for its half-metallic behavior. The present work provides compelling evidence that controlling oxygen vacancies can be a valuable strategy to tailor the multiferroic properties of ATiO3 materials

Magnetic Ordering in Ilmenites and Corundum-Ordered Structures

In the last few years, the multiferroic materials have represented a very important research topic on the design of new technological devices. A better description for this kind of materials involves two or more forms of ferroic orders coupled in a single crystalline structure. The great number of studies in this field is focused on candidates that present the coupling between a magnetic order and ferroelectricity. However, these material classes are a challenging topic on first-principles calculations due to the strong correlation that arose from the unpaired electrons. Furthermore, the partial filling of d or f orbitals reduces a high localization and a strong interaction causing failures on the electronic structure prediction. The investigation of multiferroic materials aims at their application on the development of devices such as actuators, magnetic readers, sensors and data storage. Multiferroic materials are also alternatives to the production of technological applications based on spintronic. Our proposal is to show our experience in DFT simulations for magnetic states applied in oxides of ilmenites and corundum-ordered structures. Theoretical results reported for our group until now showed a good agreement with experimental results for half-metallicity, reduced band-gap, and/or ferromagnetic ordering

Quantum Chemistry Applied to Photocatalysis with TiO2

Heterogeneous catalysis is a topic very studied in science. Its application in technologies of energy conversion, water purification, chemical synthesis, car catalytic converter and so on is studied. Recently, the TiO2 material in anatase and rutile phases has been used extensively in photocatalytic systems; its band-gap is localized in visible and ultra-violet spectra, proportioning a good material for generation of chemical radicals. Nowadays, the density functional theory (DFT) is shown as a great tool to simulate all types of materials and the possibilities to simulate bulk and surfaces of materials importance in last few decades. Recently, quantum periodic calculations based on DFT methods have been widely used to simulate materials and the main functionals applied are PBE, PBE0 and B3LYP; they are important for doping and adsorption theoretical investigations and are present in various simulation programs, such as, Crystal, Wien, Vasp and others. This methodology has investigate the influence of dangling bonds, cationic and anionic doping, charge transfer, surface energy and more quantum properties. Quantum chemistry tools, in particular, DFT methods, are key points to develop high quality research and technology once theoretical calculations are important to guide and understand the molecular design in photocatalysis

First principle investigation of the exposed surfaces and morphology of β-ZnMoO4

Crystal shape is a critical determinant of the physical and chemical properties of crystalline materials; hence, it is the challenge of controlling the crystal morphology in a wide range of scientific and technological applications. The morphology is related to the geometry of their exposed surfaces, which can be described by their surface energies. The surface properties of β-ZnMoO4 have not yet been well explored, either experimentally or theoretically. Thus, the first-principle calculation at the density functional theory level was carried out for different low-index surfaces of β-ZnMoO4, specifically (001), (010), (110), (011), (101), and (111), and the surface energy values (Esurf) were reported. The surface stability was found to be controlled by the undercoordinated [MoOn…yVxO] and [ZnOn…yVxO] (n = 4 and 5; y = 1 and 2) clusters, i.e., their local coordination of Mo and Zn cations at the exposed surfaces, respectively, with the (111) surface being the most stable. A complete map of investigated β-ZnMoO4 morphologies was obtained using the Wulff construction and changing the values of the calculated energy surfaces. The final geometries from this map were compared with field emission-scanning electron microscopy images showing excellent agreement, prevising rectangular and hexagonal plates. Our findings will promote the use of facet engineering and might provide strategies to produce β-ZnMoO4-based materials for achieving morphology-dependent technological applications

Experimental and theoretical study of the energetic, morphological, and photoluminescence properties of CaZrO3:Eu3+

In this study, we present a combined experimental and theoretical study of the geometry, electronic structure, morphology, and photoluminescence properties of CaZrO3:Eu3+ materials. The polymeric precursor method was employed to synthesize CaZrO3:Eu3+ crystals, while density functional theory calculations were performed to determine the geometrical and electronic properties of CaZrO3:Eu3+ in its ground and excited electronic states (singlet and triplet). The results were combined with X-ray diffraction (XRD) measurements to elucidate the local structural changes induced by the introduction of Eu3+ in the crystal lattice. This process results in the formation of intermediate levels in the band-gap (Egap) region, narrowing its width. The PL emissions were rationalized by characterizing the electronic structure of the excited singlet and triplet electronic states, which provided deep insight into the main structural and electronic fingerprints associated with [CaO8], [EuO8], and [ZrO6] clusters. In addition, the Wulff construction, obtained from the first-principles calculations, was used to clarify the experimental morphologies. These results extend our fundamental understanding of the atomic processes that underpin the Eu doping of CaZrO3

Computational Chemistry Meets Experiments for Explaining the Geometry, Electronic Structure, and Optical Properties of Ca10V6O25

In this paper, we present a combined experimental and theoretical study to disclose, for the first time, the structural, electronic, and optical properties of Ca10V6O25 crystals. The microwave-assisted hydrothermal (MAH) method has been employed to synthesize these crystals with different morphologies, within a short reaction time at 120 °C. First-principle quantum mechanical calculations have been performed at the density functional theory level to obtain the geometry and electronic properties of Ca10V6O25 crystal in the fundamental and excited electronic states (singlet and triplet). These results, combined with the measurements of X-ray diffraction (XRD) and Rietveld refinements, confirm that the building blocks lattice of the Ca10V6O25 crystals consist of three types of distorted 6-fold coordination [CaO6] clusters: octahedral, prism and pentagonal pyramidal, and distorted tetrahedral [VO4] clusters. Theoretical and experimental results on the structure and vibrational frequencies are in agreement. Thus, it was possible to assign the Raman modes for the Ca10V6O25 superstructure, which will allow us to show the structure of the unit cell of the material, as well as the coordination of the Ca and V atoms. This also allowed us to understand the charge transfer process that happens in the singlet state (s) and the excited states, singlet (s*) and triplet (t*), generating the photoluminescence emissions of the Ca10V6O25 crystals

Pré-eclâmpsia : rastreamento universal ou prevenção universal para países de baixa e média-renda?

Pre-eclampsia (PE) is a severe disorder that affects up to 8% of all pregnancies and represents an important cause of maternal and perinatal morbidity and mortality. The screening of the disease is a subject of studies, but the complexity and uncertainties regarding its etiology make this objective a difficult task. In addition, the costs related to screening protocols, the heterogeneity of the most affected populations and the lack of highly effective prevention methods reduce the potential of current available algorithms for screening. Thus, the National Specialized Commission of Hypertension in Pregnancy of the Brazilian Association of Gynecology and Obstetrics Federation (Febrasgo, in the Portuguese acronym) (NSC Hypertension in Pregnancy of the Febrasgo) considers that there are no screening algorithms to be implemented in the country to date and advocates that Aspirin and calcium should be widely used.A Pré-eclâmpsia (PE) é uma doença grave que acomete ~8% das gestações e representa importante causa de morbimortalidade, tanto materna quanto perinatal. O rastreamento da doença émotivo de estudos, porém a complexidade e as incertezas quanto a sua etiologia tornam esse objetivo bastante difícil. Além disso, os custos relacionados com o rastreamento, a heterogeneidade das populações mais afetadas e ainda a falta de métodos de prevenção de grande eficácia reduzem o potencial dos algoritmos de rastreamento. Assim, a Comissão Nacional Especializada sobre Hipertensão na Gravidez da Federação Brasileira das Associações de Ginecologia e Obstetrícia (CNE Hipertensão na Gravidez da FEBRASGO) considera que não há algoritmos de rastreamento que possam ser aplicados no país nesse momento e defende a utilização dos métodos de prevenção como ácido acetilsalicílico e cálcio de maneira ampla

Pré-eclâmpsia/Eclâmpsia

Pre-eclampsia is a multifactorial and multisystemic disease specific to gestation. It is classically diagnosed by the presence of hypertension associated with proteinuria manifested in a previously normotensive pregnant woman after the 20th week of gestation. Pre-eclampsia is also considered in the absence of proteinuria if there is target organ damage. The present review takes a general approach focused on aspects of practical interest in the clinical and obstetric care of these women. Thus, it explores the still unknown etiology, current aspects of pathophysiology and of the diagnosis, the approach to disease prediction, its adverse outcomes and prevention. Management is based on general principles, on nonpharmacological and on pharmacological clinical treatment of severe or nonsevere situations with emphasis on the hypertensive crisis and eclampsia. Obstetric management is based on preeclampsia without or with signs of clinical and/or laboratory deterioration, stratification of gestational age in < 24 weeks, between 24 and less than 34 weeks, and ≥ 34 weeks of gestation, and guidance on route of delivery. An immediate puerperium approach and repercussions in the future life of pregnant women who develop preeclampsia is also presented.A pré-eclâmpsia é uma doença multifatorial e multissistêmica específica da gestação. É classicamente diagnosticada pela presença de hipertensão arterial associada à proteinúria em gestante previamente normotensa após a 20a semana de gestação. A pré-eclâmpsia também é considerada na ausência de proteinúria se houver lesão de órgão-alvo. A presente revisão tem uma abordagem geral focada em aspectos de interesse prático na assistência clínica e obstétrica dessas mulheres. Assim, explora a etiologia ainda desconhecida, aspectos atuais da fisiopatologia e do diagnóstico e diagnóstico diferencial de convulsões, a abordagem da predição da doença, seus resultados adversos e prevenção. A conduta baseia-se em princípios gerais, tratamento clínico não farmacológico e farmacológico de situações graves ou não graves, com ênfase na crise hipertensiva e eclâmpsia. O controle obstétrico se fundamenta na pré-eclâmpsia sem ou com sinais de deterioração clínica e/ou laboratorial, estratificação da idade gestacional abaixo de 24 semanas, entre 24 e menos de 34 semanas e 34 ou mais semanas de gestação e orientação na via de parto. Uma abordagem imediata do puerpério e repercussões na vida futura de gestantes que desenvolvem pré-eclâmpsia também foram apresentadas

Análise e avaliação de riscos na actividade de manutenção de juntas de dilatação em obras de arte rodoviárias

Relatório de Estágio para obtenção do grau de Mestre em Engenharia Civil na Área de Especialização de EdificaçõesO presente relatório é o resultado de um estágio realizado num ambiente real de trabalho, promovido pelo Instituto Superior de Engenharia de Lisboa (ISEL), em consonânciacom a empresa Freyssinet – Terra Armada, Pré-esforço, Estudos e Construções, S.A., no contexto do Mestrado em Engenharia Civil, perfil de Edificações. O estudo em questão compreende a identificação de riscos profissionais e respectiva Análise dos Riscos associada à actividade de manutenção de Juntas de Dilatação em obras de arte rodoviárias, com o objectivo de realizar uma Avaliação de Riscos e posteriormente, apresentar Instruções Técnicas de Segurança que contribuam para melhorar as condições de Segurança na actividade acima referida. A metodologia utilizada para a identificação dos perigos foi o Método das Energias. Os acidentes de trabalho foram classificados com base no EEAT (EUROSTAT 2001), sendo o “contacto – modalidade da lesão” o que define a natureza do risco. A Avaliação dos Riscos e o Nível de Risco foi determinado com base na matriz e nos critérios da norma OHSAS –British Standard 8800:2004. Através desta Avaliação de Riscos foi possível concluir sobre quais os principais riscos inerentes à actividade da manutenção de Juntas de Dilatação, e também entender sobre quais existe maior exposição. Com base neste estudo foram propostas medidas de segurança específicas para a totalidade dos riscos identificados, e posteriormente, foram elaborados procedimentos e instruções de segurança, com o intuito de virem a ser implementados na empresa em trabalhos futuros da mesma natureza.Abstract: The present report is the result of a post-graduate training performed in a real work environment, promoted by the Instituto Superior de Engenharia de Lisboa (ISEL), in consonance with the company Freyssinet – Terra Armada, Pre-stress, Studies and Constructions, S.A., in the context of the Master's degree in Civil Engineering, profile of Edifications This study includes the identification of occupational risks and respective Risk Analysis associated to the maintenance activity of Expansion Joints on road bridges, in order to accomplish a risk assessment and thereafter, the presentation of Technical Safety Instructionswhich contributes to improve the Safety conditions on the activity referred to above. The methodology used for the dangers identification was the Energies Method. The occupational accidents were classified based in the EEAT (EUROSTAT 2001), being the "contact - modality of the injury" what defines the nature of the risk. The Risk Assessment and Risk Level was determined based on the matrix and the criteria of the norm OHSAS –British Standard 8800:2004. Through this Risk Assessment was possible to conclude about which the principal risks inherent to the maintenance activity of Expansion Joints, and also understand about which exists greater exposure. Based on this study were proposed specific security measures for all the risks identified, and thereafter, were developed safety procedures and instructions, with the intention that they will be implemented in the company in future works of the same nature