[en] We report the characterization of LaMnO_3.15, LaCoO₃ and LaFeO₃ powders synthesized using a simple Pechini-type, polymerizable complex method based on polyesterification between citric acid and ethylene glycol. The microstructure was evaluated by scanning electron microscopy. Raman spectra measured at 300 K, excited by a He-Ne laser were studied. Pure perovskite powders of LaMnO_3.15 and LaCoO₃ with rhombohedral symmetry and LaFeO₃ with orthorhombic symmetry were formed at thermal treatments as low as 550 deg. C. The mean particle size was in the nanoscale range

[en] In this research we report the characterization of LaMnO_3+d powders synthesized by the polymerized complex method based on the Pechini-type reaction. High-quality nanopowders with controlled stoichiometry and microstructure were prepared at 700 deg. C, with mean particle sizes of approximately 45 nm. The synthesized materials were characterized by X-ray diffraction. The structure, homogeneity and particle size of the obtained compounds during different stages were investigated by scanning electron microscopy. The surface area of the final powders was determined, and the thermal magnetization curves in the range 100-300 K were analyzed. The magnetization curves indicated the ferromagnetic behavior of the powders

[en] We present the results of experiments that assess the viability of anti-Stokes scattering to investigate in situ materials at high temperatures. Both anti-Stokes and Stokes Raman measurements have been performed at various high temperatures using hafnia as a test material. As compared with Stokes Raman spectra, anti-Stokes spectra were observed with lower thermal emission backgrounds in accordance with Planck's equation. The intensity ratio of anti-Stokes to Stokes scattering approaches 1 as the temperature increases at high temperatures satisfying the Boltzmann distribution law. These results clearly demonstrate the advantage and feasibility of anti-Stokes Raman scattering for the elimination of the thermal emission in comparison with Stokes scattering. Copyright 2001 American Institute of Physics

[en] Li-intercalated layered perovskites Li_xAB₂Na_n-3Nb_nO_3n+1 (A=K, Rb, Cs; B=Ca, Sr, Ba) with n=3 and 4 have been prepared by an electrochemical technique. For the Li_xAB₂Nb₃O₁₀ superconducting materials, the value of T_c has been found to increase up to about 5-6 K as the a-axis length increases. For Li_xCsBa₂Nb₃O₁₀ with the largest a-axis length, however, superconductivity does not appear. In addition, Li_xKCa₂NaNb₄O₁₃ shows no superconductivity

[en] Two novel Eu²⁺-activated phosphors in the Na–Sc–Si–O system were developed in this study, NaScSi₂O₆:Eu and Na₃ScSi₃O₉:Eu. NaScSi₂O₆:Eu²⁺ showed yellow emission with a peak at 555 nm under excitation at 220–430 nm. When flux-treatment was performed for NaScSi₂O₆:Eu²⁺, we found the existence of a new phase. We then succeeded in synthesis of a high-purity sample of this new compound by a parallel solution synthesis method. It was revealed that the new phase was Na₃ScSi₃O₉ with isostructure to Na₃YSi₃O₉, and Eu²⁺-activated Na₃ScSi₃O₉ exhibited photoluminescence. Na₃ScSi₃O₉:Eu showed green emission with a peak at 530 nm and a corresponding broad excitation band up to 500 nm. However, photoluminescence of Eu²⁺ was negligible for Na₃YSi₃O₉:Eu because of the stabilization of Eu³⁺ at the Y³⁺ site. - Highlights: • NaScSi₂O₆:Eu and Na₃ScSi₃O₉:Eu have been developed as novel Eu²⁺-activated phosphors. • NaScSi₂O₆:Eu exhibits yellow emission whereas Na₃ScSi₃O₉:Eu exhibits green emission. • Na₃ScSi₃O₉ is a new compound possessing an isostructure to Na₃YSi₃O₉. • Luminescence properties of Na₃MSi₃O₉:Eu depend on the size of the M³⁺ ions

[en] Zirconia doped with MgO, CaO, Y₂O₃ and rare earth oxides is a remarkable material due to its technological importance, basic scientific interest and superior synthetic properties. Knowledge of phase diagrams and thermodynamic properties is of great importance in the production and application of zirconia-based ceramic materials. Recently, thermodynamic modeling of zirconia-bearing systems has received considerable attention because of the difficulties to construct zirconia-based phase diagrams and thermodynamic properties by means of experimental methods. The modeling for binary systems can be used to check for internal consistency between thermodynamic and phase diagram data and to provide optimal thermodynamic parameters. The predicted ternary phase diagrams based on the description of the binary systems give a prospect of phase relations in the ternary systems, which have not been established experimentally and have not made it possible to design efficient experiments. The same is true of going from ternary systems to a quaternary one and so on. In the laboratory the authors are currently engaged in a thermodynamic modeling of the ZrO₂-CeO₂-REO_1.5 (RE = Rare Earth) systems with a view to develop a database for the zirconia-based systems. The present article reports on the thermodynamic analysis of the ZrO₂-CeO₂ system. The thermodynamic modeling of the C_ss (solid solution of cubic ZrO₂ and CeO₂) and T_ss (solid solution based on tetragonal ZrO₂) equilibrium in the ZrO₂-CeO₂ system has been conducted, firstly, by one of the authors using two-term lattice stability values. In view of the fact that the two-term lattice stabilities are now out of date and there has been abundant information on the ZrO₂-CeO₂ system since the previous assessment, a new assessment of this system is necessary

[en] Highly crystallized luminescent SrWO₄ film has been prepared on a tungsten substrate in an alkaline solution containing strontium ions by an electrochemical method using constant direct current of 1 mA/cm² at room temperature (25 C). This film showed only a single blue emission at 461 nm with the excitation of 248 nm at liquid nitrogen temperature (-196 C), strongly suggesting it consists of well-crystallized defect-free crystals

[en] Homogeneous metastable tetragonal (t') solid solutions of ZrO₂-x mol% CeO₂ (x = 20 and 50) were successfully synthesized by the organic polymerized complex method. The citric acid-ethylene glycol solution containing Zr and Ce ions was polymerized at about 140 C and then heat-treated at about 350 C to obtain a precursor. The black precursor was heated at 450 C and then fired up to 1,300 or 1,590 C, resulting in the homogeneous solid solutions

[en] Low-temperature phase equilibria ranging from 1,000 to 1,200 C in the ZrO₂-CeO₂ system were investigated by annealing compositionally homogeneous ZrO₂-CeO₂ solid solutions in a Na₂B₂O₇·NaF flux. The 5 mol% CeO₂ samples decomposed into monoclinic (m) and tetragonal (t) phases during annealing at 1,100 and 1,120 C, and the t-phase transformed diffusionlessly into monoclinic (m') symmetry during quenching. A eutectoid reaction, t → (m + c), was confirmed to occur at 1,055 ± 10 C, where the equilibrium compositions of the t-, m-, and c-phases were 11.2 ± 2.8, 0.9 ± 0.9, and 84 ± 1 mol% CeO₂, respectively. The equilibrium phase boundaries were almost independent of the annealing time and/or the flux:sample ratio, which indicates that the flux accelerates the reaction rate without affecting the equilibration. The previous data are discussed using metastable-stable phase diagrams. The discrepancies of the low-temperature phase diagram in the literature are attributable to either regarding the metastable phase boundaries as stable ones of ignoring the sluggish kinetics

[en] We have investigated neutron powder diffraction of YBa_2-xSr_xCu₃O_7-d with x=0, 0.4, 0.8 and 1. Their Rietveld analyses were carried out in space group Pmmm assuming two different disordering models: Model A where the O(1) is displaced from (0, 1/2, 0) to (x, 1/2, 0) so that each alternate chain has some kind of zig-zag chain and Model B where the available oxygen atoms are located at both the O(1) and O(5) sites to give full and empty Cu-O chains along the a-axis. The refinements based on model B have revealed that substitution of Sr for Ba causes an increase of isotropic temperature factor for the O(1), indicating an increasing in local oxygen disordering. This disordering in the model B is consistent with the Raman results that the defect induced mode gains intensity with increasing Sr content. A possible picture of the slight decrease of T_c in YBa_2-xSr_xCu₃O_7-d is discussed in terms of both local oxygen disordering and associated charge-transfer effect. (author)