[en] Ternary electrooptic oxides, with structures related to that of the perovskite, are used or being considered for potential utilization in optoelectronics technology. Apart from their electrooptic properties, some of these oxides present interesting photochromic and photorefractive effects during illumination. This latter effect is recently an object of much attention because of its relevance to signal and image amplification, reversible holographic storage, real time image processing and conjugated optics. It consists of a reversible light induced charge of refractive index caused by charge redistribution via the electrooptic coupling. Photo-chromic or photorefractive properties critically depend on the occurrence of appropriate centres, either impurities or lattice defects, as well as on suitable carrier transport processes. In this paper, the emphasis lies on recent developments about the defects introduced by doping, thermo-chemical reduction and irradiation

[en] The characterization of the calcination products of the precipitates obtained from the bio-oxidation with Thiobacillus ferrooxidans of sulphuric water pickling liquors has been carried out by means of Moessbauer spectroscopy, x-ray powder diffraction, infrared spectroscopy and transmission electron microscopy. The results show that a full transformation of the precipitates into α-Fe₂O₃ is achieved at temperatures higher than 850 deg. C. Calcination at 700 deg. C during two hours results in the formation of α-Fe₂O₃, ζ-Fe₂O₃ and Fe₁₂O₃(SO₄)₁₅. The Moessbauer parameters of ζ-Fe₂O₃ and Fe₁₂O₃(SO₄)₁₅ at 298 and 17K are reported

[en] LiNbO₃ is a relevant material to prepare a number of electrooptic (bulk and waveguide) devices. Moreover, its photorefractive (PR) behavior is also potentially useful for optoelectronic applications such as holographic storage and coherent optical amplification. For a full understanding and optimization of the PR effect, the lattice location and valence state of the active impurities is essential, since they determine the ionization and trapping capabilities for free carriers. So far, the information obtained with spectroscopic techniques (EPR, ENDOR, Mossbauer, optical) is not conclusive, except manganese and possible iron. In this paper the authors report on an investigation of the lattice location of Eu by ion-channeling techniques. They provide a rather direct method, largely relying on geometrical considerations, which is very adequate for semiquantitative analysis. Eu has been chosen because its heavy mass produces a RBS peak well separated from the host contributions. Results conclusively show that Eu³⁺ lies partly on both Li and Nb sites (36% 64%, respectively), but not on the intrinsic vacant lattice sites

[en] In this paper we present the results of the formation of black HgS (metacinnabar) from liquid mercury and elemental sulfur using the mechanical energy provided by a ball mill in different conditions. Metacinnabar formation was observed even after short milling times (15 min) and unreacted liquid mercury was no longer detected after 60 min of milling. The reaction mechanism was monitored with a scanning electron microscope. The impact and friction forces of milling on the Hg and S mixture resulted in the formation of metacinnabar by reducing the size of mercury drops, giving rise to microspheres, and lowering the surface tension to allow sulfur grains to become adhered at the reaction interface. After 60 min of milling, the metacinnabar formation reaction was observed to be more than 99.99% complete, yielding a Toxicity Characteristic Leaching Procedure value of 3.1 μg/L Hg. The reaction product thus complies with the limits of the most stringent Universal Treatment Standard requirements, which allow a maximum TCLP concentration of 25 μg/L.

[en] In this work, a synthetic hydroxyapatite, Bio-gel HTP, marketed by BIO-RAD^R, has been studied in order to propose a method to remove the excess fluoride present in drinking water. The removal of fluoride ions by this adsorbent has been studied as a function of solution pH, and fluoride ion concentration. Experiments of fluoride ions sorption have been carried out with the use of ¹⁸F radiotracer in solutions of NaF at several concentrations with an ion selective electrode used for fluoride analysis. The adsorption isotherms show that the best fluoride adsorption on hydroxyapatite occurs at a pH range of 7.0-7.5. At this pH value the solid presents an important capacity of subtraction of fluoride, of around of 100 mmol/100 g. (author)