Time-resolved spectroscopy studies of Gd2SiO5 : Ce3+ from spherical particles

This paper reports on time-resolved emission and excitation spectra measurement studies of Gd2SiO5:Ce3+ in powder or pellet samples, from spherical particles, in order to assign the Ce3+ ion transitions into two different symmetry sites. Samples were obtained from solid-state reaction of the spherical particles oxides, SiO2 and Gd2O3:Ce3+. From time-resolved spectroscopy measurements Ce3+ ion transitions occupying the two different gadolinium crystallographic sites in Gd2SiO5 were separated and assigned. (C) 2002 Elsevier B.V. B.V. All rights reserved.

An investigation of metal oxides which are photoluminiscent at room temperature

Amorphous thin films, based on different network formers, were processed by a soft chemical process called the polymeric precursor method. The resultant amorphous metal oxides, displayed intense photoluminescence (PL) at room temperature. Heat treatment increases the PL intensity of these materials. Theoretical ab initio calculations are correlated with the observed experimental trends. (C) 2004 Elsevier B.V. All rights reserved.

Red and blue emissions of europium doped gadolinium silicate from porous silica matrix and hydroxide carbonate with spherical shaped particles

In this work, Eu(III) and Eu(II) doped gadolinium silicates has been obtained as compact tubes starting from spherical gadolinium hydroxide carbonate using the pores of silica matrix as support and its surface as reagent. Eu(III) doped gadolinium silicate with hexagonal phase shows an interesting visible shifted charge transfer band when compared to disilicate with orthorhombic phase that was also obtained. Eu(II) gadolinium silicate has been prepared using CO atmosphere presenting an intense blue emission. The divalent europium system shows a potential application as an UV-blue converter. The samples were characterized by scanning electron microscopy (SEM), X-ray powder diffractometry (XRD) and photoluminescence spectroscopy. (C) 2002 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)

Synthesis, thermal properties and spectroscopic study of solid mandelate of light trivalent lanthanides

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

Correlation between structural data and spectroscopic studies of a new beta-diketonate complex with trivalent europium and gadolinium

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Synthesis, characterization and thermal behaviour of solid-state compounds of light trivalent lanthanide succinates

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

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.

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.

Thermal and spectroscopic studies of solid oxamate of light trivalent lanthanides

Solid-state LnL3·1.25H2O compounds, where L is oxamate and Ln is light trivalent lanthanides, have been synthesized. Simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC), experimental and theoretical infrared spectroscopy, TG-DSC coupled to FTIR, elemental analysis, complexometry, and X-ray powder diffractometry were used to characterize and to study the thermal behavior of these compounds. The results led to information about the composition, dehydration, thermal stability, thermal decomposition, and gaseous products evolved during the thermal decomposition of these compounds in dynamic air atmosphere. The dehydration occurs in a single step and through a slow process. The thermal decomposition of the anhydrous compounds occur in a single (Ce), two (Pr), and three (La, Nd to Gd) steps with the formation of the respective oxides, CeO2, Pr 6O11, and Ln2O3 (Ln = La, Nd to Gd). The theoretical and experimental spectroscopic study suggests that the carboxylate group and amide carbonyl group of oxamate are coordinate to the metals in a bidentate chelating mode. © 2012 Akadémiai Kiadó, Budapest, Hungary.

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.

High-density nanoparticle ceramic bodies: A study of heating rates in the sinterization of Gadolinium-doped Ceria

An investigation on the sinterization of Gd:CeO2 (Ce 0.85Gd0.15O1.9-δ ceramic system) 3-10 nm nanoparticles in pressed bodies was done. The heating rate was taken as a key parameter and two competing sinterization processes were identified, associated with different diffusional mechanisms. Using heating rates of 113 C min -1, a high-final density (98 % of the theoretical) was obtained by superposing the two aforementioned mechanisms, resulting in a homogeneous microstructure at lower temperatures. © 2012 Akadémiai Kiadó, Budapest, Hungary.