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.     

Subsolidus phase equilibria in the SrO-Bi2O3-B2O3 system

Phase equilibria in the SrO-Bi₂O₃-B₂O₃ system were studied using powder X-ray diffraction (XRD) and differential thermal analysis (DTA). Quasi-binary sections were determined, and an isothermal section of the system in the subsolidus region at 600°C was constructed using the crossing spections method. A new ternary compound was found: SrBi₂B₄O₁₀. The existence of SrBi₂B₂O₇ was verified. Bi₂O₃-SrB₂O₄ and Bi₄B₂O₉-2SrO: 3B₂O₃ polytherms were constructed.     

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.     

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.     

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.     

Facile Fabrication of Porous Bi2O3 Microspheres by Thermal Treatment of Bi2O2CO3 Microspheres and its Photocatalysis Properties

β- and α-phase porous Bi₂O₃ microspheres with an average size of around 4 μm had been synthesized by thermal treatment of Bi₂O₂CO₃ microspheres at 350 and 400–500 °C respectively in an air atmosphere. The Bi₂O₂CO₃ microspheres had been synthesized at a temperature of 180 °C by a hydrothermal process using Bi(NO₃)₃ as the bismuth source with the assist of citric acid. By combining the results of X-ray powder diffraction, transmission electron microscope, scanning electron microscopy, and UV–Visible absorption spectra, the structural, morphological and optical properties characterization of the products were performed. The photocatalytic activity of the as-prepared α- and β-phase porous Bi₂O₃ microspheres have been tested by degradation of methylene orange under visible light, indicating that porous β-Bi₂O₃ microspheres showed enhanced photocatalytic performance compared to P25 and α-Bi₂O₃ microspheres.     

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.     

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.     

Study of the liquidus in the system Bi2O3TiO2

The liquidus in the system Bi₂O₃TiO₂ has been determined in the range 2 to 22 mole % TiO₂ by a thermobalance technique and by DTA. It has been confirmed that Bi₁₂TiO₂₀ melts incongruently at 875°C and that the eutectic composition between Bi₁₂TiO₂₀ and Bi₂O₃ melts at 795°C.     

Untersuchungen zum quasibinären System Bi2Se3/BiI3

Investigations on the Pseudobinary System Bi₂Se₃/BiI₃ The phase diagram of the pseudobinary system Bi₂Se₃/BiI₃ was investigated by DTA, total pressure measurements and x-ray phase analysis. Only BiSeI exist as a ternary phase in this system. The compound melts incongruently at 545 °C. Heat of formation and standard entropy were calculated from vapor pressure data.ΔH_B° (BiSeI, f, 298) = (–23.4 ± 1.9) kcal/mol S°(BiSeI, f, 298) = (38.7 ± 3.5) cal/K · mol     

Phase relations in the MgO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Phase relations in the MgO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. No ternary compounds have been found in the system. Quasi-binary sections have been the 600°C determined and isothermal section of the system has been constructed.     

Solid State Phase Formation in the Bi2O3-PbO-CaO System

Following our previous research, this work is dedicated to the study of phase formation in the subsolidus domain of the Bi₂O₃-PbO-CaO system. Former investigations performed by DTA/TGA and XRD have pointed out that under non-isothermal conditions only the formation of binary compounds occurs. Under such conditions these compounds could be non-equilibrium phases. In order to establish the conditions of formation of equilibrium phases, a study of the Bi₂O₃-PbO-CaO system, in isothermal conditions, was carried out. The results obtained in isothermal conditions have confirmed the presence of Bi₂O₃-rich solid solutions and Ca₂PbO₄ as main equilibrium phases. An attempt to represent the phase relations of the mentioned system at 700°C should be equally mentioned. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Studies on the System ZnO-V2O5-Fe2O3 Reactivity of ZnFe2O4 Towards ZnV2O6

Studies on the reactivity of ZnFe₂O₄ towards ZnV₂O₆ revealed that in the solid state the phases interact in a molar ratio of 1:3 to form a new compound, to which the molecular formula Zn₂FeV₃O₁₁ was assigned. The compound melts congruently at 825±5°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,Characterization and Oxide Ionic Conductivity of Binary β‐(Bi2O3)1‐x(Lu2O3)x System

In this research, the effects of doping Lu₂O₃ to α‐Bi₂O₃ in the range of 0.01 < x < 0.10 in a series of different mole fractions (1% < n < 10% mole ratios) was studied. Beside, heat treatment was performed by applying a cascade temperature rise in the range of 700‐800 °C for 72 hours and new phases were obtained in the (Bi₂O₃)_1‐x(Lu₂O₃)_x system. After heat treatment for 72 hours at 800 °C; mixtures, containing 2‐8% mole Lu₂O₃, formed a tetragonal phase. As a result of subjecting mixtures, containing 9% and 10% mole Lu₂O₃, to a quenching process at 825 °C, tetragonal phases were obtained. With the help of XRD, the crystal systems and lattice parameters of the solid solutions were obtained and their characterization was carried out. Thermal measurements were made by using a simultaneous DTA/TG system. The total conductivity (σ_T) in the β‐Bi₂O₃ doped with Lu₂O₃ was measured using the four‐probe DC method.     

Nanosized bismuth titanate (Bi4Ti3O12) system drive through auto-combustion process by using suspension titania (TiO2)

Bismuth titanate (Bi₄Ti₃O₁₂) was developed by means of titanium oxide (TiO₂) suspension in auto-combustion process at 220 °C to get nanosized (20 ± 5 nm) bismuth titanate (Bi₄Ti₃O₁₂) powder. Complete piezoelectric phase (tetragonal) was obtained after calcination at 700 °C. Dilatometery of compacts was performed to find out sintering temperature. On the basis of shrinkage results, compacts were sintered at 750, 800, and 850 °C for 2 h. After sintering single phase was obtained with orthorhombic structure analyzed by X-ray diffraction and also investigated by Rietveld method. High-resolution scanning electron microscopy revealed that fine plate-like structure which is a characteristic of BIT powder can be obtained at 850 °C. Sintering results indicate that density and average grain size increase with the increasing temperature. A maximum of about 90 % of the theoretical density was achieved for the sintered product at 850 °C.     

Crystallization of MgFe2O4 from a glass in the system K2O/B2O3/MgO/P2O5/Fe2O3

Spherical magnetic Mg-Fe-O nanoparticles were successfully prepared by the crystallization of glass in the system K₂O/B₂O₃/MgO/P₂O₅/Fe₂O₃. The magnetic glass ceramics were prepared by melting the raw materials using the conventional melt quenching technique followed by a thermal treatment at temperatures in the range 560–700 °C for a time ranging from 2 to 8 h. The studies of the X-ray diffraction, electron microscopy and FTIR spectra confirmed the precipitation of finely dispersed spherical (Mg, Fe) based spinel nanoparticles with a minor quantity of hematite (α-Fe₂O₃) in the glass matrix. The average size of the magnetic nano crystals increases slightly with temperature and time from 9 to 15 nm as determined by the line broadening from the XRD patterns. XRD studies show that annealing the glass samples for long periods of time at temperature ≥604 °C results in an increase of the precipitated hematite concentration, dissolution of the spinel phase and the formation of magnesium di-borate phase (Mg₂B₂O₅). For electron microscopy, the particles were extracted by two methods; (i) replica extraction technique and (ii) dissolution of the glass matrix by diluted acetic acid. An agglomeration of the nano crystals to larger particles (25–35 nm) was observed.     

Gesamtdruckmessungen und Gasphasenzusammensetzung über Re2O7, ReO3 und ReO2

Total Pressure Measurements and Gas Phase Composition over Re₂O₇, ReO₃, and ReO₂ The total pressures over Re₂O₇, ReO₃, and ReO₂ have been determined by means of a membrane pressure gauge. The sublimation pressure over Re₂O₇ will be measureable at a temperature above 225°C and amounts 230 Torr at the melting point (at 315°C). The values are . ReO₃ decomposes at a temperature above 400°C according to with ΔH°_r,T = 214.6 ± 2kJ/mol and ΔS°_r,T = 263.2 ± 4J/K · mol. ReO₃ is not detectable in the gaseous phase in measurable quantities. ReO₂ decomposes at a temperature above 800°C according to with ΔH°_r,T = 387,0 ± 8.4 kJ/mol and ΔS°_r,T = 289.1 ± 12.5 J/K · mol.     

Phase relations in the system ZnV2O6 -ZnFe2O4

Using DTA and XRD methods, a diagram of phase equilibria in ZnV₂O₆-ZnFe₂O₄ system has been constructed. System ZnV₂O₆-ZnFe₂O₄ is in subsolidus area a real binary system and its components form a compound Zn₂FeV₃O₁₁. Zn₂FeV₃O₁₁ melts incongruently at 835±5°C with deposition of two solid phases: b-Zn₂V₂O₇ and ZnFe₂O₄. This revised version was published online in July 2006 with corrections to the Cover Date.     

The compounds and the phase diagram of MoO3-Rich Bi2O3MoO3 system

The equilibrium phase diagram between 0 and slightly above 50 mole% Bi₂O₃ in the Bi₂O₃MoO₃ system has been studied by differential thermogravimetric analysis (DTA) and X-ray diffraction measurements on fused mixtures and single crystals. The results confirm the existence of the four compounds α (Bi₂O₃·3MoO₃), β (Bi₂O₃·2MoO₃), γ (Bi₂O₃·MoO)₃ and ? (～1.3Bi₂O₃·MoO₃) in the system. However, the phase diagram as well as the nature of melting of the α and γ were found disagreed with previous results. The γ compound melts incongruently at 947°C, whereas the α compound melts congruently at 662°C. The crystal class and lattice parameters of the compounds were determined based on the single crystal as well as powder pattern techniques. The results show that all four compounds have the monoclinic structure. The unit cell parameter of the β, γ, and ? compounds were found to be quite different from previously reported data. The lattice parameters obtained from X-ray analysis were also verified by density measurements of the single crystals. The polymorphism of the compounds was also investigated with single crystal samples. No polymorphic transformations for the α, β, and γ phases were detected in the work.