Phase Relations in the Solidus Region of the SrO-Bi2O3-B2O3 System

Phase equilibria in the SrO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. Ternary compounds SrBiBO₄ and Sr₇Bi₈B₁₈O₄₆ congruently melting at 820 ± 5°C and 760 ± 5°C have been found. Quasi-binary sections are determined and the isothermal section of the system in the region Bi₂O₃-Sr₂Bi₂O₆-Sr₃B₂O₆-B₂O₃ at 600°C has been constructed.     

Phase relations in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system in the subsolidus region

Phase relations in the CaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction and differential thermal analyses, and the isothermal section at 600°C has been constructed. The formation of ternary compounds at the component ratios 1CaO: 1Bi₂O₃: 1B₂O₃ (CaBi₂B₂O₇) and 1CaO: 1Bi₂O₃: 2B₂O₃ (CaBi₂B₄O₁₀) has been established X-ray diffraction characteristics of these phases are presented.     

Untersuchungen zum System Bi2O3/BiI3

Investigations on the System Bi₂O₃/BiI₃ The temperature functions of decomposition pressures of the ternary compounds on the quasibinary line Bi₂O₃/BiI₃ were determined by total pressure measurements and mass spectrometry. The barogram of the system was constructed and the melting diagram precised. The enthalpies of formation and the standard entropies of the solid phases were derived from the decomposition functions: (Values see Inhaltsübersicht).     

Untersuchungen zum System Bi2O3/BiCl3

Investigation on the System Bi₂O₃/BiCl₃ The temperature functions of decomposition pressures of the ternary compounds on the quasibinary line Bi₂O₃/BiCl₃ were determined by total pressure measurements and mass spectroscopy. The barogram of the system was constructed and the melting diagram precised. The enthalpies of formation and the standard entropies of the solid phases were derived from the decomposition functions: (Values see Inhaltsübersicht).     

Phase equilibria in the Bi2O3-BaB2O4-B2O3 system in the subsolidus region

The phase equilibria in the concentration triangle Bi₂O₃-BaB₂O₄-B₂O₃ of the BaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction and DTA. Barium bismuth borates of the composition BaBi₂B₄O₁₀ and BaBiB₁₁O₁₉ have been found to exist. These borates melt at 730 and 807°C, respectively. The quasi-binary sections have been determined. It has been shown that the isothermal section of the Bi₂O₃-BaB₂O₄-B₂O₃ in the subsolidus region at 600°C is characterized by 13 triangles of coexisting phases.     

Untersuchungen zum System Bi2O3/BiBr3

Investigation on the System Bi₂O₃/BiBr₃ The temperature functions of decomposition pressures of the ternary compounds on the quasibinary line Bi₂O₃/BiBr₃ were determined by total pressure measurements. The barogram of the system was constructed and the melting diagram precised. The enthalpies of formation and the standard entropies of the solid phases were derived from the decomposition functions (Values see “Inhaltsübersicht”).     

Solid-state reactions in Y2O3:3Al2O3:4B2O3 system studied by FTIR spectroscopy and X-ray diffraction

In the Y₂O₃:3Al₂O₃:4B₂O₃ system infrared absorption spectroscopy and X-ray diffraction have been used to study the solid-state reactions in the 600–1300°C temperature range. The expected YAl₃(BO₃)₄ formation (whose optimum temperature is at about 1150°C) was proceeded and accompanied by the appearance of YBO₃ and Al₄B₂O₉ intermediate phases. At higher temperatures the Al₁₈B₄O₃₃ phase was also identified with both methods. Based on these results, some chemical reactions were suggested.     

Sur la Stoechiométrie de la Variété Allotropique γ de Bi2O3

On the Stoichiometry of the Allotropic Variation γ-Bi₂O₃ The study of the solid solutions Bi₁₂[BBi□_1/5]O₂₀ (B^+V = As, V) with 0 ? x ? 0,80 leads for x = 0,77 to a phase whose cubic centered symmetry and parameter (10.255 Å) correspond to those previously announced for γ-Bi₂O₃. The présence of impurities seems required to obtain such a phase whose theoretical stoichiometry should be Bi₁₂[Bi□_1/5]O₂₀ i. e. Bi₂O_3,125.     

Synthesis and properties of magnetically separable Fe3O4/TiO2/Bi2O3 photocatalysts

The Fe₃O₄/TiO₂/Bi₂O₃ composites were synthesized by a sol–gel method and used as improved photocatalysts for the degradation of methyl orange (MO) under simulated sunlight at room temperature. The as-prepared Fe₃O₄/TiO₂/Bi₂O₃ composites were characterized by X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). TEM analysis reveals that the composite has a core–shell structure and diameters of Fe₃O₄ core is about 200 nm. DRS results reveal that all composites showed red shift in optical absorption. TiO₂, Fe₃O₄, and Bi₂O₃ exist mainly as separate phases in the Fe₃O₄/TiO₂/Bi₂O₃ composites based on XPS analysis. The photocatalytic degradation of MO with the prepared photocatalysts was studied under simulated sunlight illumination. Photocatalytic reactivity test indicated that the removal efficiency of MO with the Fe₃O₄/TiO₂/Bi₂O₃ photocatalyst was higher than that of pure TiO₂ and Fe₃O₄/TiO₂. Recovery rate of Fe₃O₄/TiO₂/Bi₂O₃ photocatalysts achieved 80 % after five times reuse.     

Phase formation and thermal stability of the compounds in the Bi2O3-PbO system

The scientific interest for the Bi₂O₃-PbO system has increased due to the importance of the PbO in the high-T _c superconducting phase formation in the Bi₂O₃-SrO-CaO-CuO system. Also Bi₂O₃-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi₂O₃-based solid solutions are well known as high oxygen ion conductors.Previously, several low melting defined compounds have been identified in the system: 6Bi₂O₃·PbO; 3Bi₂O₃·2PbO; 4Bi₂O₃·5PbO; 4Bi₂O₃·6PbO and Bi₂O₃·3PbO.This work deals with the phase formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi₂O₃/PbO ratio, the compound 6Bi₂O₃·PbO is preferentially formed, followed by the compound 4Bi₂O₃·5PbO. The formation of the compound 4Bi₂O₃·6PbO was not confirmed while the formation of the compound Bi₂O₃ 3PbO occurs through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530–780°C.     

Phase equilibria in the BaO-Bi2O3-B2O3 system

Phase equilibria in the BaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. Quasi-binary sections have been determined, and an isothermal section of the system in the subsolidus region has been constructed. The BaO-Bi₂O₃-B₂O₃ ternary system has been divided into 22 triangles of coexisting phases. It has been found that four bismuth barium borates exist, namely, Ba₃BiB₃O₉, BaBi₂B₄O₁₀, BaBiB₁₁O₁₉, and BaBiBO₄. Ba₃BiB₃O₉ undergoes a phase transition at 850°C and exists up to 885°C, where it decomposes in the solid state. BaBiB₁₁O₁₉ and BaBi₂B₄O₁₀ melt congruently at 807 and 730°C, respectively. BaBiBO₄ melts incongruently at 780°C. X-ray powder diffraction data for the low-temperature polymorph of Ba₃BiB₃O₉ are presented.     

Synthesis and characterization of rare-earth doped SrBi2Nb2O9 phase in lithium borate based nanocrystallized glasses

Glass composites comprising of un-doped and samarium-doped SrBi₂Nb₂O₉ nanocrystallites are fabricated in the glass system 16.66SrO-16.66[(1−x)Bi₂O₃-xSm₂O₃]-16.66Nb₂O₅-50Li₂B₄O₇ (0?x?0.5, in mol%) via the melt quenching technique. The glassy nature of the as-quenched samples is established by differential thermal analyses. Transmission electron microscopic studies reveal the presence of about 15 nm sized spherical crystallites of the fluorite-like SrBi_1.9Sm_0.1Nb₂O₉ phase in the samples heat treated at 530 °C. The formation of layered perovskite-type un-doped and samarium-doped SrBi₂Nb₂O₉ nanocrystallites with an orthorhombic structure through the intermediate fluorite phase is confirmed by X-ray powder diffraction and micro-Raman spectroscopic studies. The influence of samarium doping on the lattice parameters, lattice distortions, and the Raman peak positions of SrBi₂Nb₂O₉ perovskite phase is clarified. The dielectric constants of the perovskite SrBi₂Nb₂O₉ and SrBi_1.9Sm_0.1Nb₂O₉ nanocrystals are relatively larger than those of the corresponding fluorite-like phase and the precursor glass.     

Selective reaction and chemical anisotropy in epitaxial bismuth layer-structured ferroelectric thin films

Bismuth layer-structured ferroelectric thin films consisting of a stacking of pseudoperovskite and bismuth oxide blocks along the c-axis were epitaxially grown on single-crystal substrates by metalorganic chemical vapor deposition (MOCVD), and a selective reaction of the bismuth oxide layer with HCl was demonstrated. Epitaxial films with contrasting crystal orientations were used for the acid treatment in order to probe chemical anisotropy. For a/b-axis-oriented SrBi₂Ta₂O₉, Bi₄Ti₃O₁₂, and SrBi₄Ti₄O₁₅ films with sequential stacking of the two vertical blocks, notable structural selectivity of the reaction was observed only for SrBi₂Ta₂O₉. For this film, the pseudoperovskite block remained and the bismuth oxide block was removed, while both blocks of Bi₄Ti₃O₁₂ and SrBi₄Ti₄O₁₅ dissolved into the acid. In addition to the bismuth, the other cations in the pseudoperovskite blocks, strontium and titanium, also decreased for Bi₄Ti₃O₁₂ and SrBi₄Ti₄O₁₅. The selective reaction observed for a/b-axis-oriented SrBi₂Ta₂O₉, however, was not observed for c-axis-oriented SrBi₂Ta₂O₉ films in which the pseudoperovskite and bismuth oxide blocks were stacked horizontally. The results clearly show that SrBi₂Ta₂O₉ has sub-nano-order structural selectivity and chemical anisotropy in the unit cell in the reaction with HCl.     

Preparation of SrBi2Ta2O9 from Metal Alkoxides

SrBi₂Ta₂O₉ (SBT) has potential application in FERAM. Some problems in the sol-gel processing of SBT, such as the solubility of metal alkoxides, chemical modification with a chelating reagent and crystallization behavior of the gels, are investigated.The starting solutions were prepared with Sr(OC₄H₉)₂, Bi(OC₃H₇)₃, and Ta(OC₂H₅)₅. Ethoxyethanol and acetylacetone (ACAC) were used as solvent and chelating reagent, respectively. Ta- and Bi-alkoxide are chemically modified with ACAC, but Sr-alkoxide was not. The SBT solution was stabilized with ACAC for ca. 3 months. After hydrolysis of the SBT solution with the addition of ACAC, a monolithic and transparent gel was obtained at room temperature in 100 days. The X-ray diffraction peaks of SBT and very weak peaks of SrTa₂O₆ (ST) and SrBi₂O₄ (SB) were found after calcination at 700°C for both of the gels obtained with and without addition of ACAC. In contrast, the stronger peaks of ST and SB were observed for the powder mixture of SrCO₃, Bi₂O₃, and Ta₂O₅ after calcination at 800°C. These results show the better homogeneity of the gels.     

Phase Equilibrium in the SeO2–Bi2O3 System

The subject of the present study is the system SeO₂-Bi₂O₃ that comprises two oxides with low melting points. All batches are thermal treatment in quartz ampoules, which are evacuated and sealed at a pressure P=0.1 Pa. On the basis of DTA (differential thermal analysis) and X-ray data, the most probable liquidus line of the system has been plotted. The eutectic composition lies about 90 mol% SeO₂,with on eutectic temperature at 230°C. Above 20 mol% Bi₂O₃ the liquidus temperature extremely increases. The formation of three compounds is proved:Bi₂Se₃O₉ and Bi₂Se₄O₁₁ are melting incongruently at 540 and 350°C respectively and Bi₂SeO₅ congruently at 915°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synergy effects in mixed Bi2O3, MoO3 and V2O5 catalysts for selective oxidation of propylene

In this work, the possible synergy effects between Bi₂O₃, MoO₃ and V₂O₅, and between Bi₂Mo₃O₁₂ and BiVO₄, were investigated. The catalytic activity of the ??mechanical mixture?? of these compounds was measured. The mixture containing 36.96?mol% Bi₂O₃, 39.13?mol% MoO₃ and 23.91?mol% V₂O₅ (21.43?mol% Bi₂Mo₃O₁₂ and 78.57?mol% BiVO₄), corresponding to the compound Bi_1?x/3V_1?x Mo _x O₄ with x?=?0.45 (Bi_0.85V_0.55Mo_0.45O₄), exhibited the highest activity for the selective oxidation of propylene to acrolein. The mixed sample prepared chemically by a sol?Cgel method possessed higher activity than that of mechanical mixtures.     

(Solid+Liquid) Equilibria in the Quaternary System Na2B4O7-MgB4O7-K2B4O7-H2O at 288 K

(Solid+Liquid) phase equilibria in the quaternary system Na₂B₄O₇‐MgB₄O₇‐K₂B₄O₇‐H₂O at 288 K were studied experimentally using the method of isothermal solution saturation. Solubility of any single salt in the solution of the quaternary system was determined experimentally. Based on the experimental data achieved, the phase diagram and water content diagram of the quaternary system were constructed, respectively. In the phase equilibrium diagram of the quaternary system Na₂B₄O₇‐MgB₄O₇‐K₂B₄O₇‐H₂O at 288 K, there are one invariant point E, three univariant curves E1E, E2E and E3E, and three fields of crystallization corresponding to Na₂B₄O₇·10H₂O, K₂B₄O₇·4H₂O and MgB₄O₇·9H₂O. The experimental results show that potassium borate (K₂B₄O₇·4H₂O) have higher solubilities than the magnesium borate and sodium borate in the quaternary system Na₂B₄O₇‐MgB₄O₇‐K₂B₄O₇‐H₂O at 288 K.     

Thermodynamic measurement of (Al2O3 + B2O3) system by double Knudsen cell mass spectrometry

Thermodynamic properties of B₂O₃ in the (Al₂O₃ + B₂O₃) binary system were investigated by vapor pressure measurement of B₂O₃ in equilibrium with (Al₂O₃ + B₂O₃) compounds or melts using double Knudsen cell mass spectrometry. The Gibbs free energy change of formation of Al₁₈B₄O₃₃ (9Al₂O₃·2B₂O₃) was estimated from the vapor pressure in equilibrium with a mixture of Al₁₈B₄O₃₃ and Al₂O₃ at 1573 K to 1673 K. And activities of B₂O₃ in the two-phase region Al₁₈B₄O₃₃ and B₂O₃-rich liquid, and (Al₂O₃ + B₂O₃) melts were obtained at 1373 K to 1423 K by vapor pressure measurements.     

Effect of surface melting on the formation and growth of nanocrystals in the Bi2O3-Fe2O3 system

Formation of nanocrystals in the Bi₂O₃-Fe₂O₃ system prepared by the co-precipitation of bismuth and iron hydroxides has been studied. The temperature of onset of the BiFeO₃ and Bi₂Fe₄O₉ nanocrystals formation is correlated with the melting point of the non-autonomous phases. The optimal temperature of BiFeO₃ and Bi₂Fe₄O₉ nanoparticles synthesis is 460–520 and 500–550°C, respectively.     

Raman scattering investigations on lanthanum-doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ferroelectrics

The ferroelectric ceramics of Bi₄Ti₃O₁₂, SrBi₄Ti₄O₁₅, and lanthanum-doped Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅ were synthesized, and their Raman spectra were investigated. La-doping resulted in the enlargement of remnant polarization of Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅. The structure of the Bi₂O₂ layers and TiO₆ octahedra of the intergrowth was found to be different from those of Bi₄Ti₃O₁₂ and SrBi₄Ti₄O₁₅. La³⁺ ions exhibit pronounced selectivity for the occupation of A site as La content is lower than 0.50, and tend to be incorporated into Bi₂O₂ layers when the La content is higher than 0.50. Lanthanum substitution brings about the structural phase transition in Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅. The variation of ferroelectric property may be attributed to combined contribution from the decreasing of the oxygen vacancies, the relaxation of the lattice distortion, the destroying of the insulation and the space charge compensation effects of the Bi₂O₂ slabs.