[en] We introduce a self-consistent tight-binding approach to the modeling and prediction of magnetic structure in solids. The method is similar to a charge self-consistent tight-binding method which we introduced earlier, but here we add information concerning the dependence of the ion energy on the total ion spin in the on-site matrix elements of the tight-binding Hamiltonian. We self-consistently determine both spins and charges of the ions during calculation. We illustrate with studies of MnF₂ and the rutile form of MnO₂. In the first case we find without adjustment that the well-known two sublattice spin structure is predicted. In the second case we find that a disordered spin phase is predicted, contrary to experimental evidence, but a small adjustment of the parametrization yields the spiral spin structure suggested by experiments

[en] Adsorption of sodium poly(acrylate) (PA) on rutile particles in aqueous dispersion was studied. Two different molecular weights of PA (2,100 and 30,000) and two different grades of rutile were used. Various pHs, ionic strengths, and PA concentrations were investigated. The main technique employed was measurement of the transverse NMR relaxation of the solvent using the CPMG pulse sequence. Other techniques used to augment these results include electroacoustics, scanning electron microscopy, and measurement of the adsorbed amount of PA by a fluorescence spectroscopy technique using the dye acridine orange. Adsorption of small ions such as Na⁺, K⁺, Cl^-, and NO₃^- to the particle surface was found to have a significant effect on the measured transverse relaxation rate, that was dependent on the pH and the concentration of the ions. There was usually an additional effect on the relaxation due to the adsorbed PA, but only qualitative rather than quantitative information about the adsorption could be deduced. At pH 4 especially, it could be seen that the results were consistent with the common assertion that polymers adsorb in a flat conformation at low concentration, and only become looped when all of the surface sites are full. At pH 10 it was found that the relaxation rate for the longer chain PA samples fluctuated over time, indicating metastable PA conformations. There were also unusual trends in the relaxation rate for these samples, which could be due to a previously proposed small ion complexation mechanism for PA adsorption at high pH in this system. It is possible that an extensive and comprehensive study using this technique, investigating all of the relevant parameters, especially the effect of small ion adsorption, may allow a quantitative description of the adsorbed conformation. (author)

[en] Tamil Nadu, the southernmost state with second longest coast line in India has many placer heavy mineral deposits. These deposits contain economically important light heavy minerals like ilmenite, rutile, leucoxene, monazite, zircon, garnet, sillimanite, kyanite and non-economic minerals like pyroxenes, amphiboles and magnetite along with associated accessory minerals like staurolite, epidote, spinel, biotite and tourmaline. Geologically, granulitic rocks, principally Khondalites (garnet-sillimanite-graphite gneisses), charnockites and granitic gneisses bordered by sedimentary rocks are exposed along the eastern coastal plains of the Tamil Nadu. The principal highland areas, as for example, Shavaroys, Nilgiris, Palni-Kodaikanal Hills and Cardomom hills consists primarily of Charnockites. The margins of highland show a gradation into less metamorphosed rocks generally of amphibolite facies. The khondalites are found south of Kodaikanal massif. Anorthosites and layered mafic complexes occur at Sittampundi, Kadavur areas. Alkaline rocks and carbonatites are prominent at Simalpatti, Sevattur and Sivamalai. Coastal sedimentaries include, Gondwanas, Cretaceous, Tertiary and Quaternary rocks along with lateritic soils and beach sands

[en] In order to reduce the sun-burn effect in a sample of the bolometric material Nb:TiO_2−x, oxygen annealing was carried out. This effect can be examined by comparing thermal stability test results between the as-deposited and oxygen-atmosphere-annealed samples under high-temperature exposure conditions. Structural studies confirm the presence of amorphous and rutile phases in the as-deposited and annealed samples, respectively. Composition studies reveal the offset of oxygen vacancies in the Nb:TiO_2−x samples through oxygen-atmosphere annealing. The oxygen atoms were diffused and seemed to occupy the vacant sites in the annealed samples. As a result, the annealed samples show better thermal stability performance than the as-deposited samples. The universal bolometric parameter (β) values were slightly decreased in the oxygen-annealed Nb:TiO_2−x samples. Although bolometric performance was slightly decreased in the oxygen-annealed samples, high thermal stability would be the most essential factor in the case of special applications, such as the military and space industries. Finally, these results will be very useful for reducing the sun-burn effect in infrared detectors. (paper)

[en] Pyrochlore-rich and zirconolite-rich ceramics have been developed for the immobilization of excess weapons Pu. The ceramics are composed of a mixture of pyrochlore, zirconolite, brannerite and rutile. Impurity ions are present in most Pu-waste streams. Most of these impurities can be incorporated into the phases present in the ceramic; however some, such as B and Si, can promote the formation of additional phases. In this work, the impurity ions were classed into sets with supposedly the same valency (2+, 3+, 4+, 5+ and 6+). One set containing Np and Th and another set containing the glass formers (Al, Si, B, Na and K) were also made. These sets of elements were then added to a 'baseline' ceramics of nominal sintered composition, 95 wt.% pyrochlore (Ca_0.89Gd_0.22(Pu or Ce)_0.22U_0.44Hf_0.23Ti₂O₇) and 5 wt.% HF-doped rutile, (Ti_0.9Hf_0.1O₂). A sufficient amount of each of these sets of impurity ions was added so that the primary phases of the baseline ceramic were saturated with them and secondary phases formed. Both Pu/U-doped Ce/U-doped samples were made. The impurity elements were added as nitrates to an alkoxide-route precursor, which was calcined and then ball milled. Pellets were pressed from the powder and sintered in Ar, air or 3.7% H₂ in Ar at about 1350 degrees Celsius for 4 hours. The obtained results are summarized in this work. As a matter of fact, most of the ions can be accommodated in the ceramic, but the partitioning across the different phases in the ceramic is not even. The groups will preferentially move to certain phases or, if sufficient amounts are present, result in the formation of new phases. The conclusion is that all ions of similar size and valency behave in a similar manner unless there are volatility problems

[en] The electronic structure of TiO₂ aerogels is studied by soft x-ray absorption near-edge structure (XANES) spectroscopy. High-resolution O K-edge and Ti L_2,3-edge XANES spectra of aerogels are compared with those of rutile, anatase, and unrelaxed amorphous phases of full-density TiO₂. Results show that all the main spectroscopic features of aerogels, reflecting the element-specific partial density of empty electronic states and correlation effects, can be attributed to the absence of long-range order in stoichiometric amorphous TiO₂. Based on these results, we discuss the effects of short- and long-range order on the electronic structure of TiO₂

[en] This work is about the laboratory scale investigation of the conditions in the rutile synthetic production from one me nita in Aguas Dulces reservoir. The iron mineral is chlorinated and volatilized selectively leaving a residue enriched in titanium dioxide which can be used as a substitute of rutile mineral

[en] Thin titanium dioxide (TiO₂) semiconductor layer with different scattering layers are investigated in dye-sensitized solar cells (DSSCs). Usually, the scattering layer is placed after the photoanode films in order to harvest more incidents light. The scattering layer based on rutile phase TiO₂ is prepared, and placed in the different position of the photoanode films (on the surface of the FTO glass, between the two layers of transparent TiO₂ film and after the transparent TiO₂ film). We use STT, TST and TTS as marks (T and S represent the transparent TiO₂ layer and the scattering layer respectively). The result of this study indicates that STT which has the lowest incident light harvesting efficiency demonstrates the highest electron collection efficiency, while TTS which has the highest incident light harvesting efficiency sacrifices the electron collection efficiency greatly. It is discovered that TST, of which the incident light harvesting efficiency basically remains unchanged compared to TTS, reveals higher electron collection efficiency and achieves the maximum photovoltaic conversion efficiency (7.0%). By applying UV-Visible and diffuse reflectance spectroscopy, electrochemical impedance spectroscopy (EIS), the effects of the incident light harvesting and electron collection efficiencies on different cells are analyzed. It makes the best use of this scattering layer and has a reference for the application of other scattering layer types

[en] This work compares two alternative methods of characterizing the nonlinearities in a 10 x 10 mm² superconducting thin film. Both methods are based on measuring the intermodulation distortion in high temperature superconducting (HTS) films. The first method measures the unpatterned film by using a rutile loaded cavity operating at the TE₀₁₁ mode. The second method is based on intermodulation measurements made in a resonant coplanar line which is patterned on the same film that is used in the rutile cavity. In both experiments we use closed-form expressions and numerical techniques to extract local parameters related to the nonlinearities of the superconductor. The intermodulation data in both type of measurements can be fitted with identical nonlinear parameters of the HTS

[en] In this work, we investigated the influence of the geometrical confinement effects on the fundamental thermal properties of rutile and anatase TiO₂ for both cylindrical nanostructures (CNSs) and nanotubular structures (NTSs), respectively. Calculations of energy levels are developed in the framework of effective mass approximation by generalizing the resolution of Schrödinger equation in a truncated cylinder. The energy spectrum is then used in the determination of thermodynamic properties by using the Boltzmann-Gibbs distribution. Numerical computations done for both rutile and anatase TiO₂ nanomaterials reveal a strong localization of the electron orbitals along to the lateral surface for all the studied are CNS and NTS. The average energy, heat capacity, entropy, and Helmholtz free energy calculated for different thicknesses for NTS and different cross-sections of CNS. Our numerical investigation shows that all thermodynamic properties depend on the temperature, the cross-section for the CNS, and the shell thickness for the NTS. We demonstrated that for low thickness, the heat capacity shows a Schottky-like anomaly at low temperatures. We also show that the Rutile structure is more stable than anatase. We hope that the thermodynamic properties concluded from this study can be considered as useful information for understanding the thermodynamic properties of TiO₂ nanofibers. (paper)