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The impact of the synthesis method and morphology of the LaFe 0.5 Sb 1.5 O 6 samples on their catalytic activity in CO oxidation was studied in detail. The samples obtained by solid-phase reaction and co-precipitation showed higher catalytic activity. The features of the morphology, which cause the lowering of catalytic activity, were revealed for the samples synthesized in molten salts with and without preliminary microwave-hydrothermal treatment. A comparative study of all synthesized rosiaites LnFe 0.5 Sb 1.5 O 6 , Ln = La–Pr, LaFe 0.5-x Ga x Sb 1.5 O 6 and also pyrochlore Pr 2 (Fe,Sb)O 7 using an in situ diffuse reflection IR spectroscopy method was undertaken to clarify the mechanism of CO oxidation. It was revealed that in the course of the reaction the intermediate complexes of metal carbonyls are formed on the surface. At the same time, inactive carbonyls, which exist on the of Ce- and Pr-containing samples surface before the reaction mixture is fed, were found. This feature gives rise to a decrease in their catalytic activity. A reaction mechanism occurring via intermediate carbonyl complexes on the active centers - [Sb3+ - V O - - Fe3+] – is proposed. The CO oxidation on completely gallium-substituted samples indicates the existing of an additional channel for proceeding of redox process, which is not associated with Fe3+. It is suggested that the nature of this channel is possibly associated with a rosiaite layered structure, which creates a unique environment conducive to complex adsorption phenomena. [ABSTRACT FROM AUTHOR]

The layered oxide BiGeSbO 6 has been synthesized for the first time via solid state reaction. Rietveld refinement showed that BiGeSbO 6 belongs to PbSb 2 O 6 structural type (P-31m space group) with unit cell parameters a = 5.1314(9), c = 4.9974(1) Å, α = 90°, γ = 120°, Z = 1. Using the EXAFS and XANES methods, it was shown that a structural feature of this compound is a strong disordering of the Bi–O octahedron caused by the stereochemical activity of the 6s2 lone pair of Bi3+ electrons. A model according to which one oxygen vertex in the oxygen coordinated Bi3+ octahedron is absent, and the lone pair of electrons builds this polyhedron to the octahedron, was proposed. A particularity of the structure of BiGeSbO 6 is that the existing oxygen vacancy does not have a specific position. It was established that BiGeSbO 6 does not exhibit any polymorphic transition up until its incongruent melting point Т m = 985°С. Isobaric heat capacity was measured and thermodynamic functions (entropy, enthalpy increment and Gibbs free energy) were calculated for BiGeSbO 6 in the 10–1200 K temperature range. We found that the band gap of BiGeSbO 6 is due to the allowed direct interband transition with the energy of 3.16 eV. It was shown that BiGeSbO 6 has a wide transmission region in the visible and near-IR ranges. BiGeSbO 6 is a self-activated phosphor, but its luminescence spectrum is atypical for Bi3+-containing oxides. The luminescent properties of Bi 1-x Eu x GeSbO 6 solid solutions (x = 0.3, 0.5) were also studied. [ABSTRACT FROM AUTHOR]

The series of La 1-x Pr x Ga 0.5 Sb 1.5 O 6 solid solutions (x = 0–1) with PbSb 2 O 6 structure was synthesized. The comparative study of the La 1-x Pr x Ga 0.5 Sb 1.5 O 6 morphology showed all compounds have net microstructures. Herein the Pr concentration increasing leads to particles size decreasing from 400 up to 200 nm in the samples with low Pr content and to recrystallization and coarsening of the particles in Pr-rich ones. Using LaGa 0.5 Sb 1.5 O 6 as an example, it was shown that the compounds have a wide transmission region in the visible and IR spectral ranges and are characterized by a low-energy phonon spectrum. An analysis of the spectral-luminescent characteristics revealed the presence of a cross-relaxation process (1D 2 →1G 4) → (3H 4 →3F 4) of Pr3+ ions for La 1-x Pr x Ga 0.5 Sb 1.5 O 6 at x ≥ 0.07. It was showed that a broadband radiation of thermal nature is observed under laser excitation with λ = 457 nm and a power density of J = 4.65 kW/cm2 for the samples with high (x = 0.4–1) praseodymium content. • La 1-x Pr x Ga 0.5 Sb 1.5 O 6 solid solutions with PbSb 2 O 6 structure have been synthesized. • La 1-x Pr x Ga 0.5 Sb 1.5 O 6 have a wide transmission region in the visible and IR ranges. • The presence of a cross-relaxation process (1D 2.→1G 4)→(3H 4 →3F 4) of Pr3+ was shown. • The broadband radiation of thermal nature is observed. [ABSTRACT FROM AUTHOR]

The detailed study of magnetic properties, including dc and ac measurements, has been carried out on the Bi-Cr-Sb-O pyrochlore. The region of pyrochlore phase existence was determined and photocatalytic properties have been also studied. We revealed that the Bi-Cr-Sb-O pyrochlore phase occurs along Bi 2−x Cr 1+x SbO 7 section within the region x = 0.1–0.4. The Cr 3+ ions oxidation state in Bi-Cr-Sb-O pyrochlore was confirmed by XANES spectra. The best Rietveld refinement results for Bi 1.8 Cr 1.2 SbO 7 composition were achieved for the disordered structure model (space group Fd-3m ). According to the magnetic data Bi 1.8 Cr 1.2 SbO 7 is a highly frustrated pyrochlore with short-range antiferromagnetic exchange interactions between the nearest Cr 3+ ions. At T g  = 4 К this compound undergoes spin-glass transition. [ABSTRACT FROM AUTHOR]

Phase equilibria in the La 2 O 3 -Fe 2 O 3 –Sb 2 O 5 system have been studied. The isothermal section was constructed at T=900 °С. The existence of the ternary oxide LaFe 0.5 Sb 1.5 O 6 was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe 0.5 Sb 1.5 O 6 crystallizes in a trigonal layered structure relating to PbSb 2 O 6 type (space group P-31m, a=b=5.2446(3) Å, c=5.1930(3) Å, Z=1). The fine powder of LaFe 0.5 Sb 1.5 O 6 was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe 0.5 Sb 1.5 O 6 in the applied magnetic field H=5000 Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100 Oe the magnetic data of LaFe 0.5 Sb 1.5 O 6 indicates an unusual critical behavior near phase transition at T<2 K. [ABSTRACT FROM AUTHOR]

A new composite material consisting of BiFeO 3 crystallites inside a nonmagnetic glass-like matrix has been synthesized using the glass crystallization method. The phase equilibrium and glass formation region of the Bi 2 O 3 –Fe 2 O 3 –B 2 O 3 system (0–50 mol % B 2 O 3 ) have been investigated. The optimal compositions for glass–ceramic synthesis are within the 25–85 mol % BiFeO 3 range on the Bi 4 B 2 O 9 –BiFeO 3 section. The obtained ceramics were studied by X-ray diffraction, Raman spectroscopy, microscopic and magnetic methods. It was shown that the BiFeO 3 crystallites grow according to a dendrite mechanism resulting in anisotropic glass–ceramic. Magnetic properties of the synthesized samples depend upon their morphology and crystallinity. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have constructed the isothermal section of the system Bi2O3–Fe2O3–Sb2O x . [•] Ternary compound formation is limited to pyrochlore, which forms a solid solution region. [•] The phase diagram points out that 7–25% of Bi-positions are occupied with Fe3+. [•] The Mossbauer data confirmed that Fe3+ ions enter the Bi-positions. [•] Magnetic measurements revealed spin-glass magnetic transition at 9K. [ABSTRACT FROM AUTHOR]

• Novel Eu/Tb/Dy-contained phosphors with rosiaite-type structure were synthesized. • Particle size for the Bi 1−x Ln x GeSbO 6 is higher than for the La 1−x Ln x Ga 0.5 Sb 1.5 O 6. • Bi 1−x Ln x GeSbO 6 and La 1−x Ln x Ga 0.5 Sb 1.5 O 6 exhibited different luminescent properties. • Addition of Tb3+/Dy3+ to Eu3+ changed the emission from red-orange to yellow-orange. In this work, novel phosphors LaGa 0.5 Sb 1.5 O 6 and BiGeSbO 6 doped with Eu3+, Tb3+, and Dy3+ were synthesized, and the luminescent properties were studied. The impact of the host type on the emission properties was demonstrated for compositions singly doped with Eu3+ and Dy3+ ions. For the La 1−x Eu x Ga 0.5 Sb 1.5 O 6 and Bi 1−x Eu x GeSbO 6 (x = 0.05–0.5) solid solutions, there were evident differences in the luminescence intensity ratio of the bands caused by the 5D 0 →7F 1 and 5D 0 →7F 2 transitions of Eu3+ that may have resulted from a different rare earth (RE) ion coordination environment. The spectra of all the bismuth-containing solid solutions were characterized by the appearance of an additional band related to the intrinsic luminescence of the bismuth-containing host. The intensity ratio of this band and the RE ion emission lines for dysprosium-containing compounds was much higher than that for compositions doped with praseodymium and europium. Co-doping with Eu3+, Dy3+, and Tb3+ ions led to a shift in the emission colour to orange (when doped with two types of RE ions) and yellow-orange (when doped with three types of RE ions). [ABSTRACT FROM AUTHOR]

Abstract: Bi12SiO20 crystals doped with Cu were grown by the Czochralski method along from a melt. The concentration of the impurities was determined by electro–thermal and flame atomic absorption spectroscopy. The lattice parameter was determined by single-crystal diffractometry. Results from Raman measurements in different scattering configurations lead to the conclusion that distinguishable structural distortions of the bismuth–oxygen framework of the sillenite lattice take place due to Cu doping. [Copyright &y& Elsevier]

Abstract: The Bi12TiO20 thin films with high optical quality were grown from the melt on a substrate of Bi12SiO20 and Bi12GeO20 single crystals by two methods: LPE and crystallization from finite volume (CFV). The results of experimental investigation of time evolution of light-induced absorption in BTO:Cu waveguide are presented. All structures show a nearly equidistant spectrum of n eff with intervals from 2×10−3 to 5×10−3. The time evolution of light-induced absorption is qualitatively different for the lowest and the highest modes in the waveguide. [Copyright &y& Elsevier]

Abstract: Single crystals of Bi12TiO20 doped with Cu, Ca, Zn, Cd, B, Al, Ga, V, P, Nb, Cr, Mn, Fe, Co, Ni, and their mixtures were grown by a conventional high-temperature flux method. Absorption, circular dichroism, light-induced absorption, optical activity, photoconductivity, dark conductivity and the two-beam coupling on the reflection grating are studied. [Copyright &y& Elsevier]

• Regularities of Bi 4 Ge 3 O 12 formation in hydrothermal-microwave conditions are studied. • Additives allow to reduce temperature and duration of synthesis. • Chelating agents are more effective to modify the particle shape than surfactants. • Reducing particle size helped improve scintillation properties of the material. A route for production of fine Bi 4 Ge 3 O 12 (BGO) powder is sought after to lower the cost of scintillation devices and make their shapes more versatile. A systematic study of highly dispersed BGO crystallization under the hydrothermal-microwave (HTMW) conditions was carried out in the present work. Anionic, cationic and non-ionic surfactants, chelating agents and polyols were used to modify the synthesis and their respective effects on phase composition and morphology were determined. It was shown that chelating agents or other additives that are capable of forming complexes with the bismuth ions allow the production of smaller, non-aggregated particles and have the procedure be scaleable. BGO powders of various morphology were synthesized and study of the optical properties of the product discovered their advantages over traditional single-crystal material. The BGO powders obtained in optimal HTMW conditions are characterized by the presence of a single intense fast scintillation component with a flash time of about 11 ns which is by an order of magnitude less than that observed in single-crystal BGO (327 ns). This suggests the suitability of these powders for the production of scintillation materials with improved properties. This material is promising for creating highly sensitive composite detectors with a high rate of counting events. [ABSTRACT FROM AUTHOR]

Abstract: Crystals of BSO doped with Se in two different concentrations (BSO:Se(I) and BSO:Se(II)) were grown by the Czochralski method. It is established that doping with Se is accompanied with preferential absorption of Fe from the melt. According to the in-depth chemical analysis, it is assumed that the doping Se ions enter the tetrahedral positions by means of the substitution of 3Si4+ by (Se6+ +2Fe3+) ions. The measured absorption spectrum of the low-concentration Se-doped crystal (BSO:Se(I)) confirms such a conclusion as the absorption coefficient is increased in a broad spectral interval (1.4–3.1eV) – an effect typical for all Fe-doped Bi12SiO20 crystals. The polarized Raman spectra of BSO:SeI show that the doping-induced lattice distortions are small. The IR spectrum of the BSO:SeI crystal yields indications for local lowering of the symmetry of the Fe-occupied tetrahedral positions. Doping with Se at high concentration (BSO:Se(II)) leads to occasional second phase inclusions and to a downshift of practically all modes in the Raman spectrum by 2–5.5cm−1. It is concluded that the doping with Se at high concentrations follows the same mechanism as that at low concentrations but the introduced lattice distortions are more significant, and lead to an enlargement of the unit cell while preserving the overall cubic symmetry. [Copyright &y& Elsevier]