Mixed Bismuth Research Articles

A study of the kinetics of bismuth telluride synthesis by an oxide reduction method

The kinetics of a reduction of bismuth and tellurium oxides in a hydrogen atmosphere, leading to the formation of thermoelectric bismuth telluride is investigated. The evaluation of the reaction kinetics was based on a thermogravimetric analysis performed in non-isothermal conditions. A non-parametric analysis method and the Friedman method were used for the evaluation of the data. Additionally, for a better understanding of the process, reactions of the reduction of Bi2O3, TeO2 as well as Bi2Te2O7 and Bi2Te4O11, which are formed as intermediate products, were investigated. The activation energies calculated for the reactions were between 56 kJ/mol in the case of the Bi2Te2O7 reduction and 100 kJ/mol for the reduction of mixed oxides. No correlation between the activation energy and the Bi:Te ratio in the reduced material was found. The calculated conversion functions also differed between the investigated reactions. A self-heating process was found for TeO2 and Bi2Te4O11 reduction reactions. In the case of the tellurium oxide, it was assigned to the melting of Te nanoparticles. These effects were also found to enhance the synthesis of Bi2Te3 by the reduction of mixed bismuth and tellurium oxides. The resulting thermoelectric material was found to be completely reduced, with no traces of oxygen inthe XPS spectrum. EDX mapping of the cross-section of material’s grains revealed a homogenous distribution of elements in the final product.

Hydrothermal synthesis, crystal structures, and optical properties of H[Bi3O(Te3O9)](NO3)2 and [Bi2(TeO3)2](SO4)

Two new mixed bismuth (III) tellurite nitrate/sulfate, H[Bi3O(Te3O9)](NO3)2 and [Bi2(TeO3)2](SO4) were synthesized under hydrothermal conditions. H[Bi3O(Te3O9)](NO3)2 crystallizes in the hexagonal space group P6¯ 2 m (No. 189) with lattice parameters a = 9.8465(4), b = 9.8465(4), c = 4.1917(4) Å, V = 351.95(4) Å3, Z = 1, while [Bi2(TeO3)2](SO4) crystallizes in the monoclinic space group C2/c (No. 15) with lattice parameters a = 15.7657(13), b = 7.4285(5), c = 8.0959(6) Å, β = 112.693(2)°, V = 874.75(11) Å3, Z = 4. The structure of H[Bi3O(Te3O9)](NO3)2 features one-dimensional cationic 1∞[Bi3O(Te3O9)]+ chains along c axis, which are composed of [BiO7] and [TeO4] polyhedra by sharing corners and edges, whereas [Bi2(TeO3)2](SO4) possesses a new three-dimensional framework consisting of two-dimensional zigzag layers of 2∞[Bi2(TeO3)2]2+ that are linked by SO42- anions. Title compounds were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, Raman spectra, infrared spectra and solid state UV-vis-NIR diffuse reflectance spectroscopy.

Preparation of mixed bismuth and iron thin films by pulsed laser deposition using powder targets

Bismuth iron garnet (Bi3Fe5O12) thin films, for use in magnetic optics, were prepared by a pulsed laser deposition method using Bi and Fe mixed powder targets in oxygen gas. The deposition rate of the film strongly depended on the target mixture. The X-ray diffraction and X-ray photoelectron spectroscopy results suggest that the prepared films were not Bi3Fe5O12 but Bi-rich films, because of the lower melting temperature of Bi (544 K) compared with that of Fe (1811 K).

Characterization of bismuth–cerium-molybdate selective propylene ammoxidation catalysts

Acrylonitrile is a major chemical intermediate used in the production of a wide range of chemical and polymer products. Central to the commercial process is a proprietary catalyst consisting of a complex mixture of metal oxides containing a bismuth-containing molybdate phase that is active and selective for propylene ammoxidation to acrylonitrile. Among the most active and selective is a solid solution of bismuth and cerium molybdate. Solid state structural studies were undertaken to characterize this active phase. The results show that the mixed bismuth–cerium molybdate consists of a solid solution phase having the scheelite-related structure of cerium molybdate with a monoclinic unit cell. Analysis of the cation site occupancy using synchrotron X-ray diffraction indicates that bismuth preferentially occupies the Ce(3) site of the monoclinic cerium molybdate structure. It is therefore possible to singularly identify the structure of the active site for propylene ammoxidation given that bismuth is a necessary constituent of a site for selective propylene (amm)oxidation. The proposed active site consists of bismuth located next to a cation vacancy in the structure, presumably in order to accommodate its lone pair of electrons. Bismuth serves as the site for the rate determining α-hydrogen abstraction from propylene to form an allyl intermediate and subsequent nitrogen insertion and loss of lattice oxygen. The bismuth site is surrounded by two cerium cations in this active site configuration. Thus the model that emerges from this study is Bi3+ and Ce3+ in a molybdate structural framework with cerium readily able to undergo Ce3+↔Ce4+ redox that facilitates lattice oxygen transfer to the active site as required by the operative Mars–van Krevelen mechanism for selective propylene ammoxidation. The presence of two cerium cations adjacent to bismuth as a key component of the active site is expected to promote the rapid re-oxidation of the catalytic site effecting enhanced catalytic performance with respect to selective product yields and productivity.

Morphologic characteristics of bismuth and silver particles formed upon the reduction of metal stearates with benzyl alcohol

The products of the reduction of individual and mixed bismuth oxohydroxostearate and silver stearate with benzyl alcohol are studied by electron microscopy and X-ray powder diffraction. The reduction of mixed bismuth and silver carboxylates with benzyl alcohol is a promising route to both individual submicronzised bismuth and silver metal powders and to their alloys.

209Bi NQR in Mixed Oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3

It was earlier found from nuclear quadrupole resonance (NQR) measurements and computer modeling that α-Bi2O3, Bi3O4Br and mixed oxides Bi2O3· 2Al2O3, Bi2O3· 2Ga2O3, Bi2O3· 3GeO2, and 2Bi2O3· 3GeO2exhibit local ordered magnetic fields from 30 to 200 G. It thus follows that these compounds are not diamagnets in a conventional sence of the word. With the aim of revealing previously unknown magnetic properties in bismuth(III) oxide-based Main Group element compounds, the mixed bismuth–boron oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3were prepared and studied using 209Bi NQR. The quadrupole interactions of the 209Bi nuclei and their electronic environment were studied, the crystallochemical features of the compounds were discussed, and the conformity of the 209Bi results to the X-ray structure data was verified. The preliminary tests in the field of a permanent magnet showed that the resonance intensities increase in external magnetic fields, indicating that a magnetism of unknown nature develops in the titled compounds. It was found reasonable to continue studies of the magnetic properties of these compounds using single-crystal 209Bi NQR in external magnetic fields.

Possibility of New Mixed Bismuth Layer-Structured Ferroelectrics

Possibilities of new ferroelectrics, Bi5Nb3O15 (BIN) and Bi5Ta3O15 (BTA), where A=Bi5+, B=Nb5+ and Ta5+ and k=1, in the general formula of mixed bismuth layer-structured oxides (MBLSO), Bi4A2k -1B2k +1O6k +9 (k=1, 2, 3, 4), are discussed using ordinary fired, hot-pressed and hot-forged ceramics. The lattice constants are a=5.464, b=5.340 and c=21.01 Å for BIN and a=5.434, b=5.394 and c=20.82 Å for BTA. The D-E hysteresis loop of hot-pressed BIN at 150° C indicates that BIN may be a new ferroelectric. The dielectric constant, ε s, of BTA shows a peak at about 550° C in the temperature-dependence curve of ε s.

Electrocatalysis of Anodic Oxygen‐Transfer Reactions: Oxidation of Cr(III) to Cr(VI) at Bi(V)‐Doped PbO2‐Film Electrodes

Voltammetric and coulometric results are described for the electrocatalytic oxidation of Cr(III) to Cr(VI) at the mixed bismuth(V)‐lead(IV) dioxide film electrodes (designated ) that are electrodeposited from acidic solutions of Pb(II) containing Bi(III). A current efficiency of 99.2% (σ = 1.1%, N = 12) is obtained for galvanostatic generation of Cr(VI) at a preconditioned film electrode. Preconditioning of the film merely involves the generation of Cr(VI) which, based on scanning electron micrographs, is concluded tentatively to achieve chemical stripping of noncatalytic portions of the films to produce films having greater electrocatalytic activity for the desired reaction. Electrochemical stripping of the electrode had a similar preconditioning effect. Based on wavelength dispersive spectroscopy, electrochemical stripping resulted in an increase in surface Bi concentration of 33% relative to Pb.

UHV and electrochemical transfer studies on Pt(110)-(1 × 2) : the influence of bismuth on hydrogen and oxygen adsorption, and the electro-oxidation of carbon monoxide

We have investigated the anodic stripping of bismuth layers adsorbed on Pt(110)-(1 × 2) by metal vapour deposition, and through under-potential deposition (upd) from solution. We have also studied the effect of the bismuth layers on hydrogen and oxygen adsorption in ultra-high vacuum (UHV), upd hydrogen adsorption-desorption, and the electro-oxidation of CO in dilute sulphuric acid electrolyte. A bismuth monolayer (0.7 ML) undergoes electro-oxidation at 0.77 V and 0.88 V (vs. Pd | H 2) (saturation θ Bi = 0.75), with the lowest potential anodic peak associated with the formation of the bismuth adsorbed at coverages greater than 0.5 ML in the uniaxially compressed structure. An overall charge of two electrons is associated with the oxidation process in the monolayer, whereas three electrons are involved in the anodic stripping of the second layer at 0.59 V, and third and subsequent layers at 0.5 V. Bismuth adsorption results in a linear blocking of the β2 hydrogen temperature programmed desorption (TPD) state without a shift in the desorption temperature, and total blocking of hydrogen at 0.5 ML of bismuth at the completion of the c(2 × 2) overlayer on the unreconstructed surface. The blocking of the upd hydrogen layer by bismuth is non-linear, and is fastest at lowest coverage of bismuth. At 0.5 ML coverage of bismuth, ca. 0.5 ML of upd hydrogen can be adsorbed, and at 0.7 ML of bismuth 0.25 ML of upd hydrogen is adsorbed. The bismuth does not change the potential of the upd hydrogen adsorption-desorption. CO adsorbed from solution on Pt(110)-(2 × 1) at 0.4 V produces on transfer to UHV the TPD characteristic of 1 ML of CO in the Pt(110)-(2 × 1)plgl overlayer. Electro-oxidation of this layer takes place in an anodic peak in the cyclic voltammetry at 0.69 V. CO adsorbed from solution at 0 V saturates at a coverage of 0.8 ML, and undergoes electro-oxidation at lower potentials, in a broader peak centred at 0.66 V and a small peak at 0.38 V. The effect of bismuth adsorption is to decrease the amount of CO adsorbed, and available for electro-oxidation, at the same rate as CO adsorption is blocked in UHV. Bismuth also has the effect of increasing the electrochemical potential for CO oxidation from 0.69 V on the clean surface to 0.78 V when CO is co-adsorbed with bismuth in the Pt(110)-c(2 × 2) Bi overlayer, or at higher coverages. A shift to a higher CO oxidation potential is observed from the smallest coverages studied, although at 0.1 ML the peak is broad. The electro-oxidation of the CO also strongly influences the subsequent oxidation behaviour of the bismuth which takes place in a highly asymmetric anodic peak at 1.0 V. The potential of CO oxidation in the mixed bismuth CO layer on Pt(110)-(1 × 2) is very similar to that on Pt(111), and the results are explained using a model involving substrate-mediated oxygen transfer in CO electro-oxidation.

Preparation and characterisation of mixed bismuth and ruthenium clusters; X-ray crystal structures of [Ru3(µ-H)3(CO)9(µ3-Bi)], [Ru3(CO)9(µ3-Bi)2], and [Ru4(CO)12(µ4-Bi)2

The inclusion of naked bismuth atoms into carbonyl cluster compounds of ruthenium has been achieved with the use of bismuth(III) nitrate pentahydrate, Bi(NO3)3·5H2O, as the bismuth containing reagent. We report the high-yield synthesis of [Ru3(µ-H)3(CO)9(µ3-Bi)](1) from the reaction of Bi(NO3)3·5H2O with [NBu4][Ru4H3(CO)12], the preparation of (1) and [Ru3(CO)9(µ3-Bi)2](2) from Bi(NO3)3·5H2O and Na[Ru3H(CO)11], and the preparation of [Ru4(CO)12(µ4-Bi)2](3) from Bi(NO3)3·5H2O and [Ru3(CO)12] in KOH–MeOH solution. The determination of the X-ray crystal structures of (1), (2), and (3) show that (1) has a slightly distorted tetrahedral heavy-metal framework with three hydrides, each bridging a Ru–Ru edge, that (2) has a trigonal-bipyramidal structure with the Ru3 ring capped above and below by µ3-Bi atoms, and that (3) has a square-bipyramidal metal framework with the Ru atoms defining the equatorial square plane and the Bi atoms symmetrically µ4-capping at the axial positions.

Mixed Bismuth and Titanium Oxides obtained by thermolysis of hydroxide coprecipitates

AbstractBy thermolysis of hydroxide coprecipitates of Bi(III) and Ti(IV) at medium temperatures between 500 and 660° one has obtained the following mixed bismuth and titanium oxides: Ti8TiO14, Bi2TiO5, Bi4Ti3O12 and Bi2Ti3O9. The hydroxide coprecipitates were obtained in controlled conditions, starting from Bi(No3)3 and TiO(No3)2. The thermolysis of the coprecipitates and the formation of mixed oxidic phases were investigated by means of TGA, TDA. IR and X‐rays analysis.