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Analytical formulae for electromechanical effective properties of 3-1 longitudinally porous piezoelectric materials

BRAVO-CASTILLERO, Julian; RODRIGUEZ-RAMOS, Reinaldo; GUINOVART-DIAZ, Raul; SABINA, Federico J.; AGUIAR, Adair R.; SILVA, Uziel P.; GOMEZ-MUNOZ, Jose Luis
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
67.43638%
A unidirectional fiber composite is considered here, the fibers of which are empty cylindrical holes periodically distributed in a transversely isotropic piezoelectric matrix, The empty-fiber cross-section is circular and the periodicity is the same in two directions at an angle pi/2 or pi/3. Closed-form formulae for all electromechanical effective properties of these 3-1 longitudinally periodic porous piezoelectric materials are presented. The derivation of such expressions is based on the asymptotic homogenization method as a limit of the effective properties of two-phase transversely isotropic parallel fiber-reinforced composites when the fibers properties tend to zero. The plane effective coefficients satisfy the corresponding Schulgasser-Benveniste-Dvorak universal type of relations, A new relation among the antiplane effective constants from the solutions of two antiplane strains and potential local problems is found. This relation is valid for arbitrary shapes of the empty-fiber cross-sections. Based on such a relation, and using recent numerical results for isotropic conductive composites, the antiplane effective properties are computed for different geometrical shapes of the empty-fiber cross-section. Comparisons with other analytical and numerical theories are presented. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effect of Ti and C additions on structural and magnetic properties of (Pr,Nd)-Fe-B nanocrystalline magnetic materials

MURAKAMI, R. K.; RECHENBERG, H. R.; NEIVA, A. C.; MISSELL, F. P.; VILLAS-BOAS, V.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
67.509297%
Effects of titanium carbide (TiC) addition on structural and magnetic properties of isotropic (Pr,Nd)-Fe-B nanocrystalline magnetic materials have been investigated. In this work, we investigate the effect of TiC addition on a (Pr,Nd)-poor and B-rich composition, as well as on a B-poor and (Nd, Pr)-rich composition. Rapidly solidified (Pr, Nd)-Fe-B alloys were prepared by melt-spinning. The compositions studied were (Pr(1-x)Nd(x))(4)Fe(78)B(18) (x = 0, 0.5, and 1) with addition of 3 at% TiC. Unlike the (Pr(x)Nd(1-x))(9.5)Fe(84.5)B(6) materials that present excellent values for coercive. field and energy product, the (Pr,Nd)-poor and B-rich composition alloys with TiC addition present lower values. Rietveld analysis of X-ray data and Mossbauer spectroscopy revealed that samples are predominantly composed of Fe(3)B and alpha-Fe. For the RE-rich compositions (Pr(x)Nd(1-x))(9.5)Fe(84.5)B(6) (x = 0.1, 0.25, 0.5, 0.75, and 1) with the addition of 3 at% TiC, the highest coercive field and energy product (8.4 kOe and 14.4 MGOe, respectively) were obtained for the composition Pr(9.5)Fe(84.5)B(6). (c) 2008 Elsevier B.V. All rights reserved.

Development and fabrication of an optimized thermo-electro-optic device using a Mach-Zehnder interferometer

MINA, A. M.; Medina, Hector Baez; MARTINS, G. S. P.; Chávez, Marco Isaías Alayo
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.515137%
The development and fabrication of a thermo-electro-optic sensor using a Mach-Zehnder interferometer and a resistive micro-heater placed in one of the device`s arms is presented. The Mach-Zehnder structure was fabricated on a single crystal silicon substrate using silicon oxynitride and amorphous hydrogenated silicon carbide films to form an anti-resonant reflective optical waveguide. The materials were deposited by Plasma enhanced chemical vapor deposition technique at low temperatures (similar to 320 degrees C). To optimize the heat transfer and increase the device response with current variation, part of the Mach-Zehnder sensor arm was suspended through front-side bulk micromachining of the silicon substrate in a KOH solution. With the temperature variation caused by the micro-heater, the refractive index of the core layer of the optical waveguide changes due to the thermo-optic effect. Since this variation occurs only in one of the Mach-Zehnder`s arm, a phase difference between the arms is produced, leading to electromagnetic interference. In this way, the current applied to the micro-resistor can control the device output optical power. Further, reactive ion etching technique was used in this work to define the device`s geometry...

Visible and near-infrared luminescent Eu(3+) or Er(3+) doped laponite-derived xerogels and thick films: Structural and spectroscopic properties

TRONTO, Jairo; RIBEIRO, Sidney Jose Lima; VALIM, Joao Barros; GONCALVES, Rogeria Rocha
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.558696%
Laponite-derived materials represent promising materials for optical applications. In this work, Eu(3+)- or Er(3+)-doped laponite xerogels and films were prepared from colloidal dispersion. Homogeneous, crack-free and transparent single layers were deposited on soda-lime substrates with a thickness of 10 mu m. Structural and spectroscopic properties were analyzed by thermal analyses, X-ray diffractometry, transmission electron microscopy, infrared spectroscopy, and luminescence spectroscopy. The addition of a rare earth ion to the laponite does not promote any changes in thermal stability or phase transition. Laponite clay was identified after annealing up to 500 degrees C, with a decrease in basal spacing when the annealing temperature is changed from 100 degrees C to 500 degrees C. Enstatite polymorphs and amorphous silicate phases were observed after heat treatment at 700 degrees C and 900 degrees C. Stationary and time-dependent luminescence spectra in the visible region for Eu(3+), and (5)D(0) lifetime are discussed in terms of thermal treatment and structural evolution. In the layered host, the Eu(3+) ions are distributed in many different local environments. However, Eu(3+) ions were found to occupy at least two symmetry sites...

Effects of Self-Assembled Materials Prepared from V(2)O(5) for Lithium Ion Electroinsertion

GALIOTE, Nelson A.; CAMARGO, Maiui N. L.; IOST, Rodrigo M.; CRESPILHO, Frank; HUGUENIN, Fritz
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.7104%
Self-assembled materials consisting of V(2)O(5), polyallylamine (PAR) and silver nanoparticles (AgNPs) were obtained by the layer-by-layer (LbL) method, aiming at their application as electrodes for lithium-ion batteries and electrochromic devices. The method employed herein allowed for linear growth of visually homogeneous films composed of V(2)O(5), V(2)O(5)/PAH, and V(2)O(5)/PAH/AgNP with 15 bilayers. According to the Fourier transform infrared spectra, interaction between the oxygen atom of the vanadyl group and the amino group should be responsible for the growth of these films. This interaction also enabled establishment of an electrostatic shield between the lithium ions and the sites with higher negative charge, thereby raising the ionic mobility and consequently increasing the energy storage capacity and reducing the response time. According to the site-saturation model and the electrochemical and spectroelectrochemical results, the presence of PAH in the self-assembled host matrix decreased the number of V(2)O(5) electroactive sites. Thus, AgNPs were stabilized in PAR and inserted into the nanoarchitecture, so as to enhance the specific capacity. This should provide new conducting pathways and connect isolated V(2)O(5) particles in the host matrix. Therefore...

Tetragonal-cubic phase boundary in nanocrystalline ZrO(2)-Y(2)O(3) solid solutions synthesized by gel-combustion

FABREGAS, Ismael O.; Craievich, Aldo Felix; Fantini, Marcia Carvalho de Abreu; MILLEN, Ricardo P.; TEMPERINI, Marcia L. A.; LAMAS, Diego G.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.558696%
By means of synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy, we have detected, in a series of nanocrystalline and compositionally homogeneous ZrO(2)-Y(2)O(3) solid solutions, the presence at room temperature of three different phases depending on Y(2)O(3) content, namely two tetragonal forms and the cubic phase. The studied materials, with average crystallite sizes within the range 7-10 nm, were synthesized by a nitrate-citrate gel-combustion process. The crystal structure of these phases was also investigated by SXPD. The results presented here indicate that the studied nanocrystalline ZrO(2)-Y(2)O(3) solid solutions exhibit the same phases reported in the literature for compositionally homogeneous materials containing larger (micro)crystals. The compositional boundaries between both tetragonal forms and between tetragonal and cubic phases were also determined. (C) 2011 Elsevier B.V. All rights reserved.; Brazilian Synchrotron Light Laboratory (LNLS, Brazil)[D12A-XRD1-1857]; Brazilian Synchrotron Light Laboratory (LNLS); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq (Brazil)[490289/2005-3]; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq (Brazil)[490580/2008-4]; Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT); ANPCyT Agencia Nacional de Promocion Cientifica y Tecnologica (Argentina)[38309]; ANPCyT Agencia Nacional de Promocion Cientifica y Tecnologica (Argentina)[01152]; Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT); Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT); ANPCyT Agencia Nacional de Promocion Cientifica y Tecnologica (Argentina)[02288]; CONICET (Argentina)[6559]; Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina (CONICET); Latin-American Centre for Physics (CLAF); Latin-American Centre for Physics (CLAF)

Synthesis and characterization of glass-ceramic microspheres for thermotherapy

Martinelli, José Roberto; Sene, Frank Ferrer; Kamikawachi, Cristiane Naomi; Partiti, Carmen Silvia de Moya; Cornejo, Daniel Reinaldo
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.515137%
Glass microspheres containing radionuclides are used to treat liver cancer. A promising alternative therapy is being developed based on the magnetic hyperthermia which is related to the heat supplied by a magnetic material under an alternating current magnetic field. The advantage of this option is that most of killed cells are cancer cells which are more susceptible to the temperature raise. In the present work aluminum iron silicate glasses containing minor glass modifiers and nucleating agents were synthesized as irregular shape particles which were further transformed in microspheres by using a petrol liquefied gas-oxygen torch. The optimized processing parameters which lead to microspheres that give a response to the magnetic field were determined. The dissolution rate in water at 90 degrees C was determined to be 3 x 10(-8) g cm(-2) min(-1). The microsphere size distribution was determined by laser scattering. The crystalline phase responsible for the ferromagnetic response was identified as magnetite. Since this phase has a high saturation magnetization and high Curie temperature, it is potentially useful for biomedical applications. The hysteresis magnetic loop was measured for materials produced in different conditions, and some of them showed to be appropriated for thermotherapy. The ratio Fe(3+)/Fe(total) was determined by Mossbauer spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.

Influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite

CVEJIC, Z.; ANTIC, B.; KREMENOVIC, A.; RAKIC, S.; Goya, Gerardo Fabian; Rechenberg, Hercilio Rodolfo; JOVALEKIC, C.; SPASOJEVIC, V.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.5636%
In this work we report results on the influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite. A series of Fe(2.85)RE(0.15)O(4) (RE = Gd, Dy, Ho, Tm and Yb) samples have been prepared by high energy ball milling. Structure/microstructure investigations of two selected samples Fe(2.85)Gd(0.15)O(4) and Fe(2.85)Tm(0.15)O(4), represent an extension of the previously published results on Fe(3)O(4)/gamma-Fe(2)O(3), Fe(2.85)Y(0.15)O(4) and Fe(2.55)In(0.45)O(4) [Z. Cvejic, S. Rakic, A. Kremenovic, B. Antic, C. Jovalekic. Ph. Colomban, Sol. State Sciences 8 (2006) 908], while magnetic characterization has been done for all the samples. Crystallite/particle size and strain determined by X-ray diffractometry and Transmission electron microscopy (TEM) confirmed the nanostructured nature of the mechanosynthesized materials. X-ray powder diffraction was used to analyze anisotropic line broadening effects through the Rietveld method. The size anisotropy was found to be small while strain anisotropy was large, indicating nonuniform distribution of deffects in the presence of Gd and Tm in the crystal structure. Superparamagnetic(SPM) behavior at room temperature was observed for all samples studied. The Y-substituted Fe(3)O(4) had the largest He and the lowest M(S). We discuss the changes in magnetic properties in relation to their magnetic anisotropy and microstructure. High field irreversibility (H>20kOe) in ZFC/FC magnetization versus temperature indicates the existence of high magnetocrystalline and/or strain induced anisotropy. (C) 2008 Elsevier B.V. All rights reserved.; Serbian Ministry of Science; Serbian Ministry of Science and Environmental Protection

Influence of ceria addition on thermal properties and local structure of bismuth germanate glasses

ROJAS, S. S.; SOUZA, J. E. De; ANDREETA, Marcello Rubens Barsi; HERNANDES, Antonio Carlos
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.515137%
Bismuth germanate glasses are interesting materials due to their physical properties and their unique structural characteristics caused by the coordination changes of bismuth and germanium atoms. Glasses of the bismuth germanate system were prepared by melting/molding method and were investigated concerning their thermal and structural properties. The structural analysis of the samples was carried out by micro-Raman and Fourier transform infrared spectroscopes. It was observed that the glass structure is formed basically by GeO(4) tetrahedral units also having the formation of the GeO(6) octahedral units. BiO(2) was considered a network former by observing the presence of octahedral BiO(6) and pyramidal BiO(3) groups in the local structure of the samples. An absorption band observed at 1103 cm(-1) in the IR spectrum of the undoped glass was attributed to the Bi-O-Ge and/or Bi-O-Bi linkage vibration. The said band shifted to lower wavenumbers after the CeO(2) addition thus reflecting changes in the glass network. Cerium oxide was an efficient oxidant agent to prevent the darkening of the glasses which was probably associated to the reduction of Bi ions. However, CeO(2) was incorporated as a local network modifier in the glass structure even at concentrations of 0.2 mol%. (C) 2010 Elsevier B.V. All rights reserved.

Fluorescent AlPO(4) gels and glasses doped with Rhodamine 6G: Preparation, structural and optical characterization

LI, Rihong; ZHANG, Long; REN, Jinjun; QUEIROZ, Thiago B. de; CAMARGO, Andrea Simone Stucchi de; ECKERT, Hellmut
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.501646%
Fluorescent AlPO(4) xerogels doped with different amounts of Rhodamine 6G (Rh6G) laser dye were prepared by a one-step sal-gel process. In addition, mesoporous AlPO(4) glasses obtained from undoped gels were loaded with different amounts of Rh6G by wet impregnation. Optical excitation and emission spectra of both series of samples show significant dependences on Rh6G concentration, revealing the influence of dye molecular aggregation. At comparable dye concentrations the aggregation effects are found to be significantly stronger in the gels than in the mesoporous glasses. This effect might be attributed to stronger interactions between the dye molecules and the glass matrix, resulting in more efficient dye dispersion in the latter. The interaction of Rh6G with the glassy AlPO(4) network has been probed by (27)Al and (31)P solid-state NMR techniques. New five- and six-coordinated aluminum environments have been observed and characterized by advanced solid-state NMR techniques probing (27)Al-(1)H and (27)Al-(31)P internuclear dipole couplings. The fractional area of these new Al sites is correlated with the combined fractional area of two new Q(3Al)((0)) and Q(2Al)((0)) phosphate species observed in the (31)P MAS NMR spectra. Based on this correlation as well as detailed composition dependent studies...

Luminescence characteristics of YAP:Ce scintillator powders and composites

QUEIROZ, T. B. de; FERRARI, C. R.; ULBRICH, D.; DOYLE, R.; CAMARGO, Andrea Simone Stucchi de
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.509297%
Cerium doped yttrium aluminate perovskite YAlO(3) (YAP) powders are pursued as interesting alternatives to bulk crystals for application in scintillating devices. The emissions of these materials in the near-UV and visible spectral regions originate from electric dipole transitions between 4f and 5d energy levels of Ce(3+) and largely depend on the environment occupied by the ion. In search for improved synthesis conditions that can lead to phase pure powders with optimized structural and spectroscopic characteristics, in this work we have employed the polymeric precursor (Pechini) method to prepare crystalline and amorphous YAP:Ce powders doped with 1-10 mol% Ce(3+). Interesting composite materials were also obtained by dispersing some of the YAP:Ce powders in silica xerogels. A comparative structural and spectroscopic study of all the samples was done by XRD, FT-IR, emission, excitation and excited state lifetime measurements. In agreement with previous reports, excitation at 296 nm results in intense emission in the range 315-425 nm with an average decay time of 30 ns. (c) 2010 Elsevier B.V. All rights reserved.; FAPESP (Brazil); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); CNPq (Brazil); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); DFG (Germany); Deutsche Forschungsgemeinschaf (DFG); Alexander von Humboldt Foundation (AvH); Alexander von Humboldt Foundation

MATERIALS EDUCATION AND INNOVATION: GLOBALIZATION OPENS NEW FRONTIERS, OPPORTUNITIES AND CHALLENGES

MASCARENHAS, Sergio
Fonte: INT COUNCIL MATERIALS EDUCATION Publicador: INT COUNCIL MATERIALS EDUCATION
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
67.444023%
In this paper we consider evolutionary pressures that will influence materials education and its role in the present scenario of Globalization: Challenges, Opportunities and needs. The main evolutionary pressures are related to some major control variables: increase of global population, new emerging technologies such as nanotechnology, alternative energies related to climate change, multimedia convergence in global communications, health, hunger, economic asymmetries and violence. Of course, many other factors could be identified, but this paper considers these as an adequate minimum basis for strategic considerations related to current materials education planning for the 21st century. In conclusion, we propose an International Network Program for Materials Education Strategy, thinking globally but acting regionally.; National Research Council of Brazil; National Research Council of Brazil

Covalent attachment of 3,4,9,10-perylenediimides onto the walls of mesoporous molecular sieves MCM-41 and SBA-15

TRINDADE, Fabiane J.; FERNANDES, Glauber J. T.; ARAUJO, Antonio S.; FERNANDES JR., Valter J.; SILVA, Barbara P. G.; NAGAYASU, Rafael Y.; POLITI, Mario J.; CASTRO, Francisco L.; BROCHSZTAIN, Sergio
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.659424%
This work describes the covalent grafting of 3,4,9,10-perylenediimides (PDI), which are fluorescent dyes with very interesting optical properties, onto the walls of mesoporous molecular sieves MCM-41 and SBA-15. The mesoporous materials were first treated with 3-aminopropyltriethoxysilane (APTES) in anhydrous toluene, generating amine-containing surfaces. The amine-containing materials were then reacted with 3,4,9,10-perylenetetracarboxylic dianhydride (PTCA), generating surface-grafted PDI. Infrared spectra of the materials showed that the reaction with amino groups took place at both anhydride ends of the PTCA molecule, resulting in surface attached diimides. No sign of unreacted anhydride groups were found. The new materials, designated as MCMN2PDI and SBAN(2)PDI, presented absorption and emission spectra corresponding to weakly coupled PDI chromophores, in contrast to the strongly coupled rings usually found in solid PDI samples. The materials showed a red fluorescence, which could be observed by the naked eye under UV irradiation or with a fluorescence microscope. The PDI-modified mesoporous materials showed electrical conductivity when pressed into a pellet. The results presented here show that the new materials are potentially useful in the design of nanowires. (C) 2007 Elsevier Inc. All rights reserved.

Persistent luminescence of Eu(2+) and Dy(3+) doped barium aluminate (BaAl(2)O(4):Eu(2+),Dy(3+)) materials

STEFANI, R.; RODRIGUES, L. C. V.; CARVALHO, C. A. A.; FELINTO, M. C. F. C.; BRITO, H. F.; LASTUSAARI, M.; HOLSA, J.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
67.659424%
Polycrystalline Eu(2+) and Dy(3+) doped barium aluminate materials, BaAl(2)O(4):Eu(2+),Dy(3+), were prepared with solid state reactions at temperatures between 700 and 1500 degrees C. The influence of the thermal treatments on the stability, homogeneity and structure as well as to the UV-excited and persistent luminescence of the materials was investigated by X-ray powder diffraction, SEM imaging and infrared spectroscopies as well as by steady state luminescence spectroscopy and persistent luminescence decay curves, respectively. The IR spectra of the materials prepared at 250, 700, and 1500 degrees C follow the formation of BaAl(2)O(4) composition whereas the X-ray powder diffraction of compounds revealed how the hexagonal structure was obtained. The morphology of the materials at high temperatures indicated important aggregation due to sintering. The luminescence decay of the quite narrow Eu(2+) band at ca. 500 nm shows the presence of persistent luminescence after UV irradiation. The dopant (Eu(2+)) and co-clopant (Dy(3+)) concentrations affect the crystallinity and luminescence properties of the materials. (C) 2009 Elsevier B.V. All rights reserved.; CNPq Conselho Nacional de Desenvolvimento; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Cientifico e Tecnologico (CNPq); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundacao de Amparo A Pesquisa do Estado de Sao Paulo (FAPESP); Rede de Nanotecnologia Molecular e de Interfaces (RENAMI); Rede de Nanotecnologia Molecular e de Interfaces (RENAMI); Instituto do Milenio de Materiais Complexos (IM2C); Instituto do Milenio de Materiais Complexos (IM2C); Graduate School of Materials Research (GSMR...

Study of the oxygen vacancy influence on magnetic properties of Fe- and Co-doped SnO2 diluted alloys

Borges, Pablo Damasceno; Leite, Luisa Maria Scolfaro; Alves, Horacio Wagner Leite; Silva Junior, Eronides Felisberto da; Assali, Lucy Vitoria Credidio
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.58805%
Transition-metal (TM)-doped diluted magnetic oxides (DMOs) have attracted attention from both experimental and theoretical points of view due to their potential use in spintronics towards new nanostructured devices and new technologies. In the present work, we study the magnetic properties of Sn0.96TM0.04O2 and Sn0.96TM0.04O1.98(V (O))(0.02), where TM = Fe and Co, focusing in particular in the role played by the presence of O vacancies nearby the TM. The calculated total energy as a function of the total magnetic moment per cell shows a magnetic metastability, corresponding to a ground state, respectively, with 2 and 1 mu(B)/cell, for Fe and Co. Two metastable states, with 0 and 4 mu(B)/cell were found for Fe, and a single value, 3 mu(B)/cell, for Co. The spin-crossover energies (E (S)) were calculated. The values are E (S) (0/2) = 107 meV and E (S) (4/2) = 25 meV for Fe. For Co, E (S) (3/1) = 36 meV. By creating O vacancies close to the TM site, we show that the metastablity and E (S) change. For iron, a new state appears, and the state with zero magnetic moment disappears. The ground state is 4 mu(B)/cell instead of 2 mu(B)/cell, and the energy E (S) (2/4) is 30 meV. For cobalt, the ground state is then found with 3 mu(B)/cell and the metastable state with 1 mu(B)/cell. The spin-crossover energy E (S) (1/3) is 21 meV. Our results suggest that these materials may be used in devices for spintronic applications that require different magnetization states.; CNPq [564.739/2010-3/NanoSemiCon...

On the nu SiO infrared absorption of polysiloxane films

Chazalviel, J. -N.; Rodrigues Filho, Ubirajara Pereira
Fonte: ELSEVIER SCIENCE SA; LAUSANNE Publicador: ELSEVIER SCIENCE SA; LAUSANNE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.58805%
The infrared absorption of polysiloxanes involves a strong band at around 1050 cm(-1), attributed to the antisymmetric vibration of siloxane bridges. The splitting of this band into two components is generally attributed to coupling between next-neighbor siloxane groups along the polysiloxane chain. From a quantitative analysis of the spectra of these materials, we find that this splitting is larger when the material is in thin-film form, and that the relative intensity of the two components is polarization dependent. We show that these effects are fully understandable in the theoretical framework of infrared absorption by thin films, and are related to long-range dipolar interactions responsible for the longitudinal-transverse splitting effect in crystalline materials. As a consequence, the polarization dependence of the infrared absorption observed for thin films does not appear to be associated with an orientational ordering in the film. (c) 2012 Elsevier B.V. All rights reserved.

Origin of Anomalous Activities for Electrocatalysts in Alkaline Electrolytes

Subbaraman, Ram; Danilovic, N.; Lopes, P. P.; Tripkovic, D.; Strmcnik, D.; Stamenkovic, V. R.; Markovic, N. M.
Fonte: AMER CHEMICAL SOC; WASHINGTON Publicador: AMER CHEMICAL SOC; WASHINGTON
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.596426%
Pt extended surfaces and nanoparticle electrodes are used to understand the origin of anomalous activities for electrocatalytic reactions in alkaline electrolytes as a function of cycling/time. Scanning tunneling microscopy (STM) of the surfaces before and after cycling in alkaline electrolytes was used to understand the morphology of the impurities and their impact on the catalytic sites. The nature of the contaminant species is identified as 3d-transition metal cations, and the formation of hydr(oxy)oxides of these elements is established as the main reason for the observed behavior. We find that, while for the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) the blocking of the sites by the undesired 3d-transition metal hydr(oxy)oxide species leads to deactivation of the reaction activities, the CO oxidation reaction and the hydrogen evolution reaction (HER) can have beneficial effects from the same impurities, the latter being dependent on the exact nature of the adsorbing species. These results show the significance of impurities present in real electrolytes and their impact on electrocatalysis.; Office of Science, Office of Basic Energy Sciences, Division of Materials Science, U.S. Department of Energy [DE-AC02-06CH11357]; Office of Science...

Novel polymer electrolytes based on gelatin and ionic liquids

Leones, Rita; Sentanin, F.; Rodrigues, Luisa C.; Ferreira, Rute A. S.; Marrucho, Isabel M.; Esperanca, Jose M. S. S.; Maule, Agnieszka Joanna Pawlicka; Carlos, Luis D.; Manuela Silva, M.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.558696%
This study describes the results of the characterization of polymer electrolytes using gelatin matrix doped with europium triflate and/or different ionic liquids. Samples of solvent-free electrolytes were prepared and characterized by ionic conductivity measurements, thermal analysis, electrochemical stability, X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. Electrolyte samples are thermally stable up to approximately 220 degrees C. All the materials synthesized are totally amorphous. The room temperature conductivity maximum of this electrolyte system is based on ionic liquid 1-ethyl-3-methylimidazolium acetate, (C(2)mim)(OAc) (1.18 x 10(-4) S cm(-1) at 30 degrees C). The electrochemical stability domain of all samples is about 2.0 V versus Li/Li+. This new series of materials represents a promising alternative in polymer electrolytes research field. The preliminary studies carried out with electrochromic devices (ECDs) incorporating optimized compositions have confirmed that these materials may perform as satisfactory multifunctional component layers in the field of "smart windows". This new materials, will open a land of promising applications in many areas: optics, energy, medicine for example as membranes and separation devices...

Evaluation of the micro-hardness and fracture toughness of amorphous and partially crystallized 3CaO center dot P2O5-SiO2-MgO bioglasses

Daguano, Juliana K. M. F.; Suzuki, Paulo A.; Strecker, Kurt; Fernandes, Maria H. F. V.; Santos, Claudinei
Fonte: ELSEVIER SCIENCE SA; LAUSANNE Publicador: ELSEVIER SCIENCE SA; LAUSANNE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.558696%
In this work, the effect of the indentation load on the results of hardness and fracture toughness, determined by Vickers micro-hardness measurements, of some glasses and glass-ceramics has been investigated. Furthermore, in order to verify the effect of crystallinity on the results, glasses of composition 52.75 wt.% 3CaO center dot P2O5, 30 wt.% SiO2 and 17.25 wt.% MgO were fused at 1600 degrees C for 4 h and annealed at 700 degrees C for 2h, and further heat-treated at 700, 775, 800 and 900 degrees C for 4h. The obtained materials were analyzed by high resolution X-ray diffraction, HRXRD, to determine the crystallization degree in function of the heat-treatment temperature. The hardness of the different specimens was determined by Vickers' micro-hardness measurements under various loads. It has been observed that with increasing crystallization of the materials their hardness increased. Furthermore, it has been possible to verify the so-called indentation size effect (ISE), i.e. hardness decreases as the indentation depth, under higher loads, increases. This effect has been more pronounced in the glass-ceramic samples. Fracture toughness has been determined by the crack length induced by the Vickers indentations and relating them to the applied loads. Glass materials presented a fracture pattern with characteristics of cleavage...

Theoretical luminescence spectra in p-type superlattices based on InGaAsN

Oliveira, Thiago F. de; Rodrigues, Sara C. P.; Scolfaro, Lusa M. R.; Sipahi, Guilherme Matos; Silva Jr., Eronides F. da
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.58805%
In this work, we present a theoretical photoluminescence (PL) for p-doped GaAs/InGaAsN nanostructures arrays. We apply a self-consistent method in the framework of the effective mass theory. Solving a full 8 x 8 Kane's Hamiltonian, generalized to treat different materials in conjunction with the Poisson equation, we calculate the optical properties of these systems. The trends in the calculated PL spectra, due to many-body effects within the quasi-two-dimensional hole gas, are analyzed as a function of the acceptor doping concentration and the well width. Effects of temperature in the PL spectra are also investigated. This is the first attempt to show theoretical luminescence spectra for GaAs/InGaAsN nanostructures and can be used as a guide for the design of nanostructured devices such as optoelectronic devices, solar cells, and others.; CNPq [564.739/2010-3/NanoSemiCon, 302.550/2011-9/PQ, 470.998/2010-5/Univ, 472.312/2009-0/PQ, 303578/2007-6/PQ, 577.219/2008-1/JP]; CNPq; CAPES; CAPES; FACEPE; FACEPE [0553-1.05/10/APQ]; FAPESP; FAPESP; Materials Science, Engineering and Commercialization Program of Texas State University; Materials Science, Engineering and Commercialization Program of Texas State University