Hardness and elastic modulus of carbon-germanium alloys

This work reports on the mechanical properties of germanium-rich amorphous carbon-germanium alloys prepared by RF sputtering of a germanium/graphite target under an argon/hydrogen atmosphere. Nano-hardness, elastic modulus and stress were investigated as a function of the carbon content. The stress, which is reduced by the incorporation of carbon, was related to the film structure and to the difference in the Ge-Ge and Ge-C bond length. Contrary to what was expected, the hardness and elastic modulus of the alloys are lower than the corresponding values for pure amorphous hydrogenated germanium film, which in turn has both properties also smaller than those of crystalline germanium. These properties are analyzed in terms of the structural properties of the films. (C) 2001 Elsevier B.V. B.V All rights reserved.

Chemical process to separate iron oxides particles in pottery sample for EPR dating

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nonlinear optical properties of antimony-germanium-sulfur glasses at 1560 nm

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Pore size evolution during sintering of ceramic oxides

This paper reviews the influence of particle size distribution, agglomerates, rearrangement, sintering atmospheres and impurities on the pore evolution of some commonly studied oxides. These factors largely affect sintering mechanisms due to modifications of diffusion coefficients or evaporation-condensation. Very broad particle size distribution leads to grain growth and agglomerates densify first. Rearrangement of particles due to neck asymmetry mainly in the early stage of sintering is responsible for a high rate of densification in the first minutes of sintering by collapse of large pores. Sintering atmospheres play an important role in both densification and pore evolution. The chemical interaction of water molecules with several oxides like MgO, ZnO and SnO2 largely affects surface diffusion. As a consequence, there is an increase in the rates of pore growth and densification for MgO and ZnO and in the rate of pore growth for SnO2. Carbon dioxide does not affect the rate of sintering of MgO but greatly affects both rates of pore growth and densification of ZnO. Oxygen concentration in the atmosphere can especially affect semiconductor oxides but significantly affects the rate of pore growth of SnO2. Impurities like chlorine ions increase the rate of pore growth in MgO due to evaporation of HCl and Mg(OH)Cl, increasing the rate of densification and particle cuboidization. CuO promotes densification in SnO2, and is more effective in dry air. The rate of densification decrease and pore widening are promoted in argon. An inert atmosphere favors SnO2 evaporation due to reduction of CuO. © 1990.

Particle growth during calcination of polycation oxides synthesized by the polymeric precursors method

The particle-growth kinetics of sodium niobate and zirconium titanate powders that were processed by the polymeric precursors method were studied. The growth kinetics that were studied for the particle, in the final stage of crystallization, showed that the growth process occurs in two different stages. For temperatures <800°C, the particle-growth mechanism is associated with surface diffusion, with an activation energy in the range of 40-80 KJ/mol. For temprratures >800°C, particle growth is controlled by densification of the nanometric particle cluster and by a neck-size-controlled particle-growth mechanism. The results suggest that this behavior was typical of the synthesis method, because two different polycation oxides presented the same behavior.

Magneto-optical rotation of heavy-metal oxide glasses

Magneto-optical rotation was measured at room temperature for glasses containing Bi2O3-CdO-GeO2 (BCG), and Bi2O3-PbO-GeO2-B2O3 (BPGP). A pulsed magnetic field between 50 and 80 KG was used to measure Faraday rotation at 632.8 nm as a function of the concentration of Bi and Cd for BCG and Bi and Pb for BPGB. Verdet constant as high as 0.162 min G-1 cm-1 at 632.8 nm for the BPGB sample with the highest concentrations of Bi and Cd was found. Verdet constant increases linearly with the heavy-metal concentration for the BPGB whereas it reaches some saturation for the BCG system. Measurements of the magneto-optical rotation at other wavelengths in the visible and the refractive index at 632.8 nm are also reported. © 1998 Elsevier Science B.V. All rights reserved.

Magnetic properties of spinel-type oxides NiMn2-xMexO4

New materials, based on the well-known spinel compound NiMn 2O4, have been synthesized and characterized from the magnetic point of view. The manganese cation was partially substituted in the general formula NiMn2-xMexO4, by nonmagnetic and magnetic elements, such as Me = Ga, Zn, Ni and Cr (0 × 1). Prior to the determination of their magnetic properties, the non-substituted spinel NiMn2O4 was carefully characterized and studied as a function of the oxygen stoichiometry, based on the influence of the annealing atmosphere and quenching rate. The ferrimagnetic character was observed in all samples, with a paramagnetic-to-ferromagnetic transition temperature T c stabilized at 110 K, and well defined long-range antiferromagnetic interactions at lower temperatures, which depend on the applied field and the substitute concentration. © 2006 Sociedad Chilena de Química.

Anelastic spectroscopy in superconducting oxides

Since the discovery of the high Tc superconductors, several works have been made about the different properties of these materials. Anelastic spectroscopy experiments are sensitive tools to the study of defects in solids and phase transitions. By this technique, we can distinguish the different types of atomic jumps that happen to different temperatures. The intensity of the peaks in the anelastic spectrum and the step in the torsional modulus are related with the concentration of the relaxing entities, and the position of the peaks is determined by its mobility. In this paper, the study on Bi and Sm based superconducting oxides was made by anelastic relaxation measurements using a torsion pendulum. The samples were submitted to successive thermal treatments in high vacuum, in the temperature range between 100 K and 650 K, heating rate about 1 K/min. For Bi based superconducting oxides the results shown two peaks, that were associated to interstitial oxygen mobility and to orthorhombic to monoclinic phase transition. For Sm based superconducting oxides the results shown a relaxation peak that was attributed to the jumps of the oxygen atoms in the inter-chains O1 and 05 of the lattice.

A study of the precursors and photoactivity of nanostructures of Ti oxides synthesized by the alkaline hydrothermal method

The present study describes the synthesis, characterization and photocatalytic potential of Ti oxide nanostructures of various morphologies and crystalline phases that were synthesized from 4 different precursors by the alkaline hydrothermal method. The materials were characterized by mainly X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA) and X-ray absorption spectroscopy (XAS). Also, photocatalytic potential was assessed by rhodamine B photodegradation. The materials obtained from peroxytitanium complexes (PTCs) exhibited a strong dependence on the concentration of KOH ([KOH]) used for synthesis. The pre-formed sheets of the PTCs were critical to the formation of nanostructures such as nanoribbons, and they were also compatible with the rolling up process, which can be utilized to form structures such as nanorods, nanowires or nanotubes. In the rhodamine photodegradation tests, TiO2 anatase nanostructures with six-coor inated Ti were more effective than the titanate ones (five-coordinated), despite having a smaller surface area and fewer OH groups. The lower photoactivity of the titanates was attributed to the presence of five-coordinated titanium species (TiO5), which may act as electron-hole recombination centers. Furthermore, the material with a mixture of TiO2/titanate was shown to be promising for photocatalytic applications. © 2013 by American Scientific Publishers.

Tunable plasmon resonance modes on gold nanoparticles in Er 3 +-doped germanium-tellurite glass

Relative to the Er3 +:gold-nanoparticle (Er3 +:Au-NP) axis, the polarization of the gold nanoparticle can be longitudinal (electric dipole parallel to the Er3 +:Au-NP axis) or transverse (electric dipole perpendicular to the Er3 +:Au-NP axis). For longitudinal polarization, the plasmon resonance modes of gold nanoparticles embedded in Er3 +-doped germanium-tellurite glass are activated using laser lines at 808 and 488 nm in resonance with radiative transitions of Er3 + ions. The gold nanoparticles were grown within the host glass by thermal annealing over various lengths of time, achieving diameters lower than 1.6 nm. The resonance wavelengths, determined theoretically and experimentally, are 770 and 800 nm. The absorption wavelength of nanoparticles was determined by using the Frohlich condition. Gold nanoparticles provide tunable emission resulting in a large enhancement for the 2H11/2 → 4I13/2 (emission at 805 nm) and 4S 3/2 → 4I13/2 (emission at 840 nm) electronic transitions of Er3 + ions; this is associated with the quantum yield of the energy transfer process. The excitation pathways, up-conversion and luminescence spectra of Er3 + ions are described through simplified energy level diagrams. We observed that up-conversion is favored by the excited-state absorption due to the presence of the gold nanoparticles coupled with the Er3 + ions within the glass matrix. © 2013 Elsevier B.V.

Chemical modification of the surface of alumina with alkaline earth metal oxides using the polymeric precursor method for catalysis application

In this study, modifications of alumina surface with of alkaline earth metal oxides were studied, using the polymeric precursor method. The modified compounds were characterized by X-ray diffraction, nitrogen adsorption-desorption and scanning electron microscopy. The catalytical properties of these new catalysts were evaluated for the transesterification reaction of babassu oil. It is observed that the transesterification reaction of babassu oil with methanol was successfully carried out using the modified alumina samples.

Iron oxides as proxies for characterizing anisotropy in soil CO2 emission in sugarcane areas under green harvest

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Iron oxides and quality of organic matter in sugarcane harvesting systems

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

One-dimensional silicon and germanium nanostructures with no carbon analogues

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)