Bismuth Oxide Compounds Research Articles

Aurivillius-layered Bi2WO6 nanoplates with CoOx cocatalyst as high-performance piezocatalyst for hydrogen evolution.

Developing a high-performance piezocatalyst that directly transforms mechanical energy into hydrogen is highly desirable in the field of new energy. Herein, the Aurivillius-layered Bi2WO6 (BWO) nanoplates are prepared through a hydrothermal reaction at a moderate temperature of 160 °C, and exhibit strong piezoelectric properties, enabling them to catalyze water splitting through ultrasonic-induced piezocatalysis effect. The hydrogen evolution reaction (HER) and H2O2 generation efficiencies are measured to be 0.43 and 0.36 mmol g-1 h-1, respectively. To further boost piezocatalytic performance, cobalt oxide nanoparticles are intentionally photo-deposited onto these nanoplates as cocatalyst. This configuration results in a significantly boosted HER performance with an efficiency of 3.59 mmol g-1 h-1, which is 2.8 times higher than that of pristine nanoplates and demonstrates strong competitiveness compared to other reported piezocatalysts. The cobalt oxide cocatalyst plays a crucial role in facilitating efficient charge separation and migration, increasing the charge concentration, and ultimately enhancing piezocatalytic HER activity. Overall, this work highlights the potential of Aurivillius-layered bismuth oxide compounds as efficient piezocatalysts and provides valuable insights for designing high-performance piezocatalysts in the field of new energy.

Microstructure profiling, lattice dynamics, and morphological studies on multi-excitonic vanadium bismuth oxide compound systems

Microstructure profiling, lattice dynamics, and morphological studies on multi-excitonic vanadium bismuth oxide compound systems

Photocatalytic BiOX Mortars under Visible Light Irradiation: Compatibility, NOx Efficiency and Nitrate Selectivity

The use of new photocatalysts active under visible light in cement-based building materials represents one interesting alternative to improve the air quality in the urban areas. This work undertakes the feasibility of using BiOX (X = Cl and I) as an addition on mortars for visible-light-driven NOx removal. The interaction between BiOX photocatalysts and cement matrix, and the influence of their addition on the inherent properties of the cement-based materials was studied. The NO removal by the samples ranking as follows BiOCl-cem > BiOI-cem > TiO2-cem. The higher efficiency under visible light of BiOCl-cem might be ascribed to the presence of oxygen vacancies together with a strong oxidation potential. BiOI-cem suffers a phase transformation of BiOI in alkaline media to an I-deficient bismuth oxide compound with poor visible light absorbance capability. However, BiOI-cem showed considerably higher nitrate selectivity that resulted in the highest NOx global removal efficiency. These results can make its use more environmentally sustainable than TiO2 and BiOCl cement composites.

Bismuth and antimony chalcogenides: Peculiarities of electron density distribution, unusual magnetic properties and superconductivity

Abstract Electron band structure calculations and analysis of critical points parameters in the electron density distribution in Bi2Te3, Bi2Se3, Bi2S3, α-Bi2O3, Sb2Te3, Sb2Se3 and Sb2S3 at ambient and high pressures were performed to determine interrelations between the crystal structure, unusual physical (including magnetic and superconducting) properties and peculiarities in the electron density distribution. The programming code WIEN2k was used for band structure calculations. The previously found correlation between the superconducting transition temperature Tc and the electron density Laplacian value in the bond critical point with the highest electron density was confirmed by the calculations made for crystal structures under high pressure. The revealed parameters of bond critical points indicate the significant role of charge density fluctuations in the compounds studied. The 121, 123Sb NQR spin echo envelopes assigned to the ν1 transition (Δm = 1/2–3/2) were measured for the two crystallographic positions of Sb atoms in the Sb2S3 structure. Unexpectedly deep oscillations of NQR spin echo envelopes were observed in very small (1–3 Oe) external magnetic fields, evidencing for the existence of local magnetic fields in Sb2S3 similar to those earlier observed in bismuth oxide compounds.

New bismuth borophosphate Bi4BPO10: Synthesis, crystal structure, optical and band structure analysis

New bismuth borophosphate Bi4BPO10 was obtained by spontaneous crystallization from the melt of correspondent composition at 804 °C. Crystal structure with orthorhombic lattice parameters: а = 22.5731(3) Å, b = 14.0523(2) Å, c = 5.5149(1) Å, V = 1749.34(4), Z = 8, SG Pcab was determined by X-ray powder diffraction technique. The [Bi2O2]2+ -layers, which are typical for bismuth oxide compounds, transform into cationic endless strips of 4 bismuth atoms width directed along the c-axis in Bi4BPO10. The strips combining stacks are separated by flat triangle [BO3]3− -anions within stacks. Neighboring stacks are separated by tetrahedral [PO4]3−-anions and shifted relatively to each other. Bismuth atoms are placed in 5–7 vertex oxygen irregular polyhedra. Bi4BPO10 is stable up to 812 °C, then melts according to the peritectic law. The absorption spectrum in the range 350–700 nm was obtained and the width of the forbidden band was estimated as 3.46 eV. The band electronic structure of Bi4BPO10 was modeled using DFT approach. The calculated band gap (3.56 eV) is in good agreement with the experimentally obtained data.

In-situ Formation of Bismuth-Based Iodine Waste Forms

AbstractWe investigated the synthesis of bismuth oxy-iodide and iodate compounds, in an effort to develop materials for iodine recovery from caustic waste streams and/or final waste disposal if repository conditions included ambient conditions similar to those under which the iodine was initially captured. The results presented involve the in-situ crystallization of layered bismuth oxide compounds with aqueous dissolved iodine (which resides as both iodide and iodate in solution). Although single-phase bismuth oxy-iodide materials have already been described in the context of capturing radioiodine, our unique contribution is the discovery that there is a mixture of Bi-O-I compositions, not described in the prior work, which optimize both the uptake and the degree of insolubility (and leachability) of iodine. The optimized combination produces a durable material that is suitable as a waste form for repository conditions such as are predicted at the Yucca Mountain repository (YMP) or in a similar type of repository that could be developed in coordination with iodine production via Global Nuclear Energy Program (GNEP) production cycles.

Structure and dielectric properties of the Aurivillius phase Bi2.25Ca0.5Na0.25Nb2O9

A new layered perovskite-like bismuth-oxide compound with the Bi2.25Ca0.5Na0.25Nb2O9 stoichiometry (Aurivillius phase) has been synthesized in polycrystalline form. As shown by powder x-ray diffraction, Bi2.25Ca0.5Na0.25Nb2O9 has an orthorhombic structure (sp. gr. A21am, no. 36) with unit-cell parameters a = 5.4845 A, b = 5.4549 A, and c = 24.9195 A. Rietveld analysis has been used to determine the atomic positional parameters in its unit cell and the position of the niobium ions. Nb5+ has been shown to be displaced from the center position in the oxygen octahedra by ∼0.15 A. The Nb K-edge extended x-ray absorption fine structure (EXAFS) spectrum of the new compound has been measured in the range 295 to 960 K. The 295-K EXAFS data have been used to evaluate the Nb-O bond lengths in the octahedra and the corresponding Debye-Waller factors. The bond lengths thus determined agree well with those inferred from powder x-ray data. With increasing temperature, the short Nb-O bonds become longer, while the long bonds become shorter. The dielectric properties of the new compound have been studied between room temperature and 1200 K at frequencies from 1 to 50 kHz. Bi2.25Ca0.5Na0.25Nb2O9 is shown to be a ferroelectric with a Curie temperature of 972 K.

Effect of Metastable Phases on the Structural Perfection of Single Crystals of Stable Bismuth Oxide Compounds

It is shown that a detailed understanding of metastable phase relations is crucial for the ability to grow perfect Bi4Si3O12 and Bi4Ge3O12 single crystals by the Czochralski process. The high stability of metastable states in melts of bismuth-oxide-containing systems has a marked effect on the structural perfection of the growing crystals of stable compounds. Crystals containing inclusions of metastable phases are grown from overheated melts.

Synthesis and Electrical Properties of SmBi5Fe2Ti3O18

SmBi 5 Fe 2 Ti 3 O 18, a five layered bismuth oxide compound is synthesized using a solid-state double sintering method. DC conductivity, impedance, and AC conductivity are studied in the temperature range 30–500°C and frequency range 1 kHz–1 MHz. Complex impedance plots are used to separate grain and grain boundary contributions to electrical impedance. Activation energy for DC conductivity was found to be around 1.0 eV. The results are analyzed to understand the conductivity mechanism.

Effect of cobalt on the high T c phase of the Bi1.6Pb0.4Sr2Ca2Cu3Oy system

A.c. susceptibility, X-ray diffraction (XRD), SEM and porosity studies have been performed on Bi1.6Pb0.4Sr2Ca2Cu3−xCoxOy (x=0, 0.05, 0.1) superconductors. XRD and SEM results have shown that (i) the compound with x=0 contains mixed phases of 2223 and 2212, (ii) the increase in concentration of cobalt (from x=0 to 0.1) helps the compound to attain a structure of strong 2201 and a small amount of Ca2CuO3 impurity phase. The onset temperatures of the diamagnetic signal of these superconductor samples with x=0, 0.05, and 0.1 as observed from a.c. susceptibility measurements are 106, 60 and 50 K, respectively. The highest onset temperature, 50 K, observed in the sample with x=0.1 rather than the usually reported value of 20 K associated with 2201 phase in bismuth oxide compounds, may be due to the presence of Ca2CuO3 impurity phases. SEM and porosity results show that the cobalt helps to increase the grain and pore sizes.

Oxygen Ion Conductivity in a New Class of Layered Bismuth Oxide Compounds

AbstractCompounds that consist of intergrowths between the Aurivillius phase Bi4Ti3O12 and brownmillerite-like slabs of BaMO2.5were synthesized and their oxygen ion conductivities investigated. Both BaBi4Ti3ScO14.5 and BaBi4Ti3InO14.5 display a discontinuity in their Arrhenius plots that appears to be caused by an oxygen vacancy order-disorder transition. Conductivity data for two Aurivillius phases BaBi4Ti4O15 and BaBi2Nb2O9 are included for comparison.

Superconductivity at 3.5 K in BaPb0.75Sb0.25O3: why is Tc so low?

SUPERCONDUCTING BaPb0.75Bi0.25O3, with a transition temperature (Tc ) of 12 K (ref. 1), is now widely viewed as the precursor to the recent appearance of copper oxide superconductors with record high Tc S. The observation of superconductivity near 30 K in Ba0.6K0.4BiO3 (refs 2,3) has raised serious questions as to whether conventional electron–phonon coupling is the primary pairing mechanism in the bismuth–lead oxide perovskites. Their Tc S are anomalously high, given their low densities of electronic states at the Fermi level4,5, but the debate as to the mechanism of superconductivity is far from settled (see, for example, refs 6–8). Here we report the occurrence of superconductivity at 3.5 K in a new member of the family, BaPb0.75Sb0.25O3. Its Tc , less than one-third that of BaPb0.75Bi0.25O3, is surprisingly low in view of the similarities between the two compounds. The discovery of superconductivity in BaPb0.75Sb0.25O3 establishes a series of isostructural compounds withTc S differing by an order of magnitude. This series provides the basis for further studies to elucidate the essential electronic characteristics that lead to high Tc in the bismuth oxide compounds.

Photogalvanic effects in bismuth oxide compounds in the impurity-induced absorption region

The present communication deals with the bulk photogalvanic effects (PGE) in the sillenite type crystals: Bi12XO20(X = Si, Ge, Ti). Sillenite crystals belong to the cubic class 23 or T and exhibit strong optical activity. As a result the PGE induced both by the linearly and circularly polarized light are observed, the latter effect for the case of the localized level-conduction band transitions being observed for the first time. To measure the PGE values the technique of the light polarization modulation was used, that allowed separation of the PGE from conventional photovoltaic effects.

AN X-RAY METHOD OF DETERMINING THE DEGREE OF PREFERRED ORIENTATION OF FERROELECTRIC MATERIAL WITH LAYER TYPE STRUCTURE AFTER HOT-PRESSING

The definition and an X-ray determination method of the degee of preferred orientation of ferroelectric ceramics with layer type structure after hot-pressing procedure are presented. The degree of preferred orientation can be obtained by merely determining the ratio of diffraction intensity of any one or more (00l) lines before and after hot-pressing procedure. Taking the mixed bismuth oxide compound with layer type structure PbBi4Ti4O15 as an example the suitability of this method has been proved.