Electrochemical deposition of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> for thermoelectric microdevices

The electrolyses of solutions of bismuth oxide and tellurium oxide in nitric acid with molar ratios of Bi:Te=3:3–4:3 lead to cathodic deposits of films of bismuth telluride (Bi₂Te₃), an n-type semiconductor. Current densities of 2–5 mA/cm² were applied. Voltammetric investigations showed that Bi₂Te₃ deposition occurred at potentials more negative than −0.125 V (Ag/AgCl, 3 M KCl). The deposit was identified as bismuth telluride (γ-phase) by X-ray analysis. Hall-effect measurements verified the n-type semiconducting behaviour. The films can be deposited in microstructures for thermoelectric microdevices like thermoelectric batteries or thermoelectric sensors.     

Electrophysical properties of bismuth titanates with the pyrochlore structure Bi<Subscript>1.6</Subscript>M<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ti<Subscript>2</Subscript>O<Subscript>7–δ</Subscript> (M = In,Li)

Lithium-containing bismuth titanates with the pyrochlore-type structure Bi_1.6Li_xTi₂O_7–δ were obtained for the first time. The formation of the pyrochlore phase was confirmed by X-ray diffraction analysis, scanning electron microscopy and local microanalysis. In Bi_1.6M_xTi₂O_7–δ, the lithium and indium are occupied the bismuth sites, primarily. The electrophysical properties of doped bismuth titanates were studied by impedance spectroscopy in the frequency range 1–10⁶ Hz. In the low-temperature range (of up to ~400°C), electron conductivity predominates; above 400°C, the oxygen-ion type of conductivity is revealed. In the range p(O₂) = 0.21–1 atm, the average value of the sum of ion transport numbers is 0.5 at 500–550°C. The relaxation process was found from the frequency dependences of the dielectric parameters (ε', tan δ, M''), which was of the same type for systems with different dopants (In, Li) probably due to the hopping mechanism of oxygen conductivity.     

A novel route to nanostructured bismuth telluride films by electrodeposition

We report a novel route to the fabrication of 3D nanostructured stoichiometric bismuth telluride (Bi₂Te₃) films by electrodeposition through inverse lipid cubic phases as evidenced by Small-angle X-ray Scattering (SAXS) and Helium Ion Microscopy (HIM). The nanostructured Bi₂Te₃ films were composed of interconnected nanowires with diameters of 60–150 Å.     

Preparation of bismuth telluride thin film by electrochemical atomic layer epitaxy (ECALE)

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Bi and Te on cold rolled silver substrate have been performed. The voltammetric analysis of underpotential shift demonstrates that the initial Te UPD on Bi-covered Ag and Bi UPD on Te-covered Ag fitted UPD dynamics mechanism. A thin film of bismuth telluride was formed by alternately depositing Te and Bi via an automated flow deposition system. X-ray diffraction indicated the deposits of Bi₂Te₃. Energy Dispersive X-ray Detector quantitative analysis gave a 2: 3 stoichiometric ratio of Bi to Te, which was consistent with X-ray Diffraction results. Electron probe microanalysis of the deposits showed a network structure that results from the surface defects of the cold rolled Ag substrate and the lattice mismatch between substrate and deposit. Translated from Chinese Journal of Applied Chemistry, 2005, 22 (11) (in Chinese)     

Magnetic Investigation of Various NiFe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> Ferrite Nanostructures Synthesized by Ball Milling Technique

NiFe_2?x Bi _x O₄ (x = 0, 0.1, 0.2, 0.3) nanoparticles with various grain sizes were synthesized via annealing treatment followed by ball milling of its bulk component materials. Commercially available bismuth, nickel and iron oxide powders were first mixed and then annealed at 1200 °C in an oxygen environment furnace for 4 h. The samples were then milled for 2 h by high-energy ball milling. X-ray diffraction (XRD) pattern indicated that in this stage the samples are single phase. The microstructure investigation was carried out by a scanning electron microscope with maximum magnification of 30,000. The average grain size for different samples was estimated by XRD technique and transmission electron microscopy. Magnetic behavior of the samples at room temperature was studied using an alternating gradient force magnetometry. The Néel temperature of the powders was measured by a Faraday balance. Based on magnetic studies, increase in bismuth content leads to a decrease in the saturation magnetization, coercive field and Néel temperature. This can be attributed to the substitution of Bi³⁺ ion in the ferrite system as a nonmagnetic cation.     

Electrochemical modification of Bi2S3 coatings in a nickel plating electrolyte

The electrochemical behavior of Bi₂S₃ coatings in Watts nickel plating electrolyte was investigated using the cyclic voltammetry, electrochemical quartz crystal microbalance, X-ray diffraction, and energy dispersive X-ray analysis methods. During the bismuth sulfide coating reduction in Watts background electrolyte in the potential region from −0.4 to −0.6 V, the Bi₂S₃ and Bi(III) oxygen compounds are reduced to metallic Bi, and the decrease in coating mass is related to the transfer of S²⁻ ions from the electrode surface. When the bismuth sulfide coating is reduced in Watts nickel plating electrolyte, the observed increase in coating mass in the potential region −0.1 to −0.4 V is conditioned by Ni²⁺ ions reduction before the bulk deposition of Ni, initiated by Bi₂S₃. In this potential region, the reduction of Bi(III) oxygen compounds can occur. After the treatment of as-deposited bismuth sulfide coating in nickel plating electrolyte at E = −0.3 V, the sheet resistance of the layer decreases from 10¹³ to 500–700 Ω cm. A metal-rich mixed sulfide Ni₃Bi₂S₂–parkerite is obtained when as-deposited bismuth sulfide coating is treated in Watts nickel plating electrolyte at a potential close to the equilibrium potential of the Ni/Ni²⁺ system and then annealed at temperatures higher than 120 °C.     

Untersuchung der Phasenbeziehungen in quaternären Systemen Bi2O3/Bi2Ch/Bi2Ch (Ch = S,Se, Te)

Investigations of the Phase Relations in the Quaternary Systems Bi₂O₃/Bi₂Ch /Bi₂Ch (Ch = S, Se, Te) The stability ranges in the pseudobinary systems Bi₂O₂S/Bi₂O₂Se, Bi₂O₂S/Bi₂O₂Te and Bi₂O₂Se/Bi₂O₂Te have been studied by solid state and chemical transport reactions. A complete mixed crystal Bi₂O₂(Te_xSe_1–x), 0 ≤ x ≤ 1 exists between the ternary compounds Bi₂O₂Te and Bi₂O₂Se. The thermal behaviour of the mixed crystal and the coexistence ranges have been determined by x‐ray and thermal analysis.     

Synthese und Kristallstrukturen der Wolfram(VI)-Alkin-Komplexe [W2(O)(OMe)6(Et?Se?CC?Se?Et)2] und Li[W(OMe)5(Et?Te?CC?Te?Et)]

Synthesis and Crystal Structures of the Tungsten(VI)-alkyne Complexes [W₂(O)(OMe)₆(Et? Se? C?C? Se? Et)₂] and Li[W(OMe)₅(Et? Te? C?C? Te? Et)] The title compounds have been prepared by reactions of lithium methanolate with [WCl₄(Et? Se? C?C? Se? Et)(THF)] and [WCl₄(Et? Te? C?C? Te? Et)(THF)], respectively, in diethylether suspensions. Both complexes were characterized by crystal structure determinations. [W₂(O)(OMe)₆(Et? Se? C?C? Se? Et)₂]: Space group P1 , Z = 2, structure determination with 4 320 observed unique reflections, R = 0.041. Lattice dimensions at ?70°C: a = 949.3, b = 1 225.3, c = 1 285.0 pm, α = 82.48°; γ = 82.44°; β = 81.44°. The tungsten atoms are bridged by three μ₂-O-atoms of the OMe groups; the alkyne ligands are coordinated side-on in a metallacyclopropene-like fashion. Li[W(OMe)₅(Et? Te? C?C? Te? Et)]: Space group P1 , Z = 2, structure determination with 9 381 observed unique reflections, R = 0.038. Lattice dimensions at ?70°C: a = 983.4, b = 1606.9, c = 1971.5 pm, α = 66.09°, β = 84.29°, γ = 79.83°. The lithium ions link the [W(OMe)₅(Et? Te? C?C? Te? Et)]^? anions to a trimeric ion ensemble via the O atoms of three OMe groups of each anion.     

Bi5,6Ni5I: Eine partiell oxidierte intermetallische Phase mit Kanalstruktur

Bi_5,6Ni₅I: A Partly Oxidized Intermetallic Phase with Channel Structure Bi_5,6Ni₅I was prepared from the elements by chemical vapour deposition. Single-crystal investigations (space group I2/m, a = 1 852.1(3), b = 418.45(6), c = 1 373.8(3) pm, β = 90.42(2)°, V = 1 064.7(3) · 10⁶ pm³) revealed parallel doublewalled channels of nickel and bismuth atoms. The central pseudo 5 axis of each channel is occupied by 6/5 disordered bismuth atoms per lattice translation along [010]. Double rows of iodine atoms fill the distorted hexagonal arrangement of the channels. Bi_5,6Ni₅I is stabilized by metallic bonding in the framework metal atoms and additional heteropolar interactions between bismuth and iodine atoms as well as between bismuth and nickel atoms. Bi_5,6Ni₅I shows metallic conductivity and ferromagnetic ordering below 17 K.     

Bi2Te3-Te nanocomposite formed by epitaxial growth of Bi2Te3 sheets on Te rod

Single-crystal Bi₂Te₃-Te nanocomposites with heterostructure were synthesized using a two-step solvothermal process in the presence of ethylenediaminetetraacetic acid disodium salt. The first step is the formation of the Te nanorods and the second step is to grow the Bi₂Te₃ sheets off the Te rods surface to form the Bi₂Te₃-Te nanocomposites. The products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. We demonstrate a method of an epitaxial growth of Bi₂Te₃ nanosheets perpendicular to the axis of the central Te rod and a formation process of Bi₂Te₃-Te nanocomposites is also proposed.     

Bismuth triple-decker phthalocyanine: synthesis and structure

Triclinic crystals of bismuth(III) triple-decker phthalocyanine, Bi₂Pc₃, Pc=C₃₂H₁₆N₈²⁻, were grown directly by the reaction of Bi₂Se₃ with 1,2-dicyanobenzene at 220°C. The Bi₂Pc₃ molecule is centrosymmetric with the bismuth atoms located closer to the peripheral phthalocyaninato(2−) rings than to the central ring. Each bismuth(III) ion is connected by four N-isoindole atoms to the peripheral and by four N-isoindole to the central Pc ring with average distances of 2.333 and 2.747 Å, respectively. This indicates a stronger connection of Bi(III) to the peripheral saucer-shaped macrocyclic rings than to the central rings. The neighbouring phthalocyaninato(2−) moieties in the Bi₂Pc₃ molecule are separated by a distance of 3.101(5) Å. The central Pc ring is rotated by 36.4° with respect to the peripheral ones. Differences in Bi–N bond lengths are a result of interaction of the bismuth ion with peripheral and central rings as well as the repulsion forces between two bismuth ions in the same Bi₂Pc₃ molecule, which are separated by a distance of 3.839(2) Å. The crystal packing is characterized by a distance of 3.56 Å between Pc rings of neighbouring Bi₂Pc₃ molecules.     

Synthesis and properties of bismuth oxide nanoshell coated polyaniline nanoparticles for promising photovoltaic properties

A novel heterostructure made of polyaniline (PANI) nanoparticles coated by nanolayer of bismuth oxide Bi₂O₃ was synthesized. The structure was characterized by scanning electron microscopy, X‐ray diffraction, and transmission electron microscopy. These characterizations showed that the bismuth oxide nanoshell was pure and crystalline, and has thickness in the range of 10 nm. The experiment on photoluminescence (PL) of Bi₂O₃ nanoshell coated polyaniline nanoparticle, at room temperature, shows an emission band peaked at around 385 nm. When compared with the PL spectrum of Bi₂O₃ nanoparticles, about 100 times PL enhancement was found in the PL spectrum of Bi₂O₃ nanoshell coated polyaniline nanoparticle. The current density versus voltage (J–V) measurements in dark and illumination showed that this heterojunction has 4 orders of magnitude rectification in the dark and 3 orders of magnitude rectification under illumination. The obtained power conversion efficiency of polyaniline nanoparticles coated by nanoshell of bismuth oxide (η = 7.453%) was much enhanced compared with polyaniline alone (η = 8.33 × 10^?4%) this indicates that the prepared heterostructure represents a promising photovoltaic solar cell. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterisation of electroplated Bi<Subscript>2</Subscript>(Te<Subscript>1−x</Subscript>Se<Subscript>x</Subscript>)<Subscript>3</Subscript> alloys

Composition modulated Bi₂(Te_1−xSe_x)₃ thin films were prepared on stainless steel substrates by cathodic electrodeposition. The composition was dependent on the deposition conditions. It was possible to obtain, in the same electrolyte, films with either an excess or a deficiency of bismuth in relation to stoichiometric Bi₂(Te_0.9Se_0.1)₃ by changing the deposition potential or the applied current density. The excess of bismuth was reached at the highest cathodic conditions. The variation of the crystallographic axis and the morphology with a granular structure were correlated with the presence of the Bi enrichment in the ternary. The crystallographic texture of bismuth telluride films was studied according to the electrodeposition conditions. The films presented a fibre texture, and a main orientation {11.0} was observed. Electrical and thermoelectric properties of a Bi_1.98Te_2.67Se_0.39 film were measured and showed an n-type behaviour.     

Improved performance of Bi2O3-doped MnO2 cathode on rechargeability in LiOH aqueous cell

Many attempts have been made to make the zinc-manganese dioxide (Zn-MnO₂) alkaline cell rechargeable, but all investigations are pertained to the proton insertion mechanism into MnO₂. In this paper, a new class of rechargeable bismuth oxide-doped MnO₂ electrode in lithium hydroxide (LiOH) electrolyte is described. The doping and the appropriate pH selection of the aqueous electrolyte improved the electrochemical performance of the aqueous cell. Hence, with an aim to understand the role of bismuth oxide (Bi₂O₃) during the discharge process, doped MnO₂ cathodes are characterized by various techniques like secondary ion mass spectrometry, X-ray diffraction, Fourier transform infra-red spectroscopy, and transmission electron microscopy analysis. The results suggest that the influence of the large radius of the cation (Bi₂O₃; Bi (III) ion (0.96 Å)) cannot be integrated into the spinel structure, thereby, improving the rechargeability. The electrode reaction of doped MnO₂ in LiOH electrolyte is shown to be lithium insertion while preventing the formation of a spinel structure that leads to a major formation of manganese oxy hydroxides.     

Hydrothermal Synthesis of Bismuth Sulfide (Bi2S3) Nanorods: Bismuth(III) Monosalicylate Precursor in the Presence of Thioglycolic Acid

Well-segregated bismuth sulfide (Bi₂S₃) nanorods with a high order of crystallinity have been successfully prepared from bismuth(III) monosalicylate [BiO(C₇H₅O₃)] by a simple hydrothermal reaction in H₂O at 180 °C. Bismuth(III) monosalicylate and thioglycolic acid act as the starting materials. The products were characterized by powder X-ray diffraction, Ultraviolet–Visible (UV–Vis) spectroscopy, transmission electron microscopy photoluminescence spectroscopy, and Fourier transform infrared spectra. The powder X-ray diffraction pattern shows the product belongs to the orthorhombic Bi₂S₃ phase. Their UV–Vis spectrum shows the absorbance at 328 nm, with its direct energy band gap of 2.6 eV. Bismuth salicylate, which is known to be a complex, may play a critical role as a precursor and a template for the growth of linear bismuth sulfide nanorods. Finally the influences of the reaction conditions are discussed and a possible mechanism for the formation of Bi₂S₃ nanorods is proposed.     

Exploration of New Birefringent Crystals in Bismuth d0 Transition Metal Selenites

The first examples of bismuth fluoride selenites with d⁰-TM/Te^VI polyhedrons, namely, Bi₄TiO₂F₄(SeO₃)₄ ( 1 ), Bi₄NbO₃F₃(SeO₃)₄ ( 2 ), Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ), Bi₂F₂(MoO₄)(SeO₃) ( 4 ) and Bi₂ZrO₂F₂(SeO₃)₂ ( 5 ) have been successfully synthesized under hydrothermal reactions by aliovalent substitution. The five new compounds feature three different types of structures. Compounds 1 – 3 , containing Ti^IV, Nb^V and Te^VI respectively, are isostructural, exhibiting a new 3D framework composed of a 3D bismuth oxyfluoride architecture, with intersecting tunnels occupied by d⁰-TM/Te^VI octahedrons and selenite/tellurite groups. Interestingly, compound Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ) is the first structure containing Se^IV and mixed-valent Te^IV/Te^VI cations simultaneously. Compound 4 features a new 3D structure formed by a 3D bismuth oxyfluoride network with MoO₄ tetrahedrons and selenites groups imbedded in the 1D tunnels. Compound 5 displays a novel pillar-layered 3D open framework, consisting of 2D bismuth oxide layers bridged by the [ZrO₂F₂(SeO₃)₂]⁶⁻ polyanions. Theoretical calculations revealed that the five compounds displayed very strong birefringence. The birefringence values of compounds 1 – 3 , especially, are above 0.19 at 1064 nm, which are larger than the mineral calcite. Based on the structure and property analysis, it was found that the asymmetric SeO₃ groups (and TeO₃ in compound 3 ) displayed the largest anisotropy, compared with the bismuth cations and the d⁰-TM/Te polyhedra, which is beneficial to the birefringence.     

Two-step synthesis of Bi2Te3-Te nanoarrays with sheet-rod multiple heterostructure

Bi₂Te₃-Te arrays with sheet-rod multiple heterostructure were obtained in large scale, using Te nanorod arrays as the in-situ templates under solvothermal process. The array is formed by the ordered Bi₂Te₃-Te rods where Bi₂Te₃ sheets distribute from the top face to the bottom face along the Te rod vertically. The microstructure of the heterostructure was studied through X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrical conductivity and Seebeck coefficient of the arrays were also studied. The course of reaction was monitored so as to propose a possible growth mechanism of such novel heterostructure. The key for the preparation of such heterostructure is to balance the velocity between the dissolution of Te rods and the formation of Bi₂Te₃ sheets. This synthetic approach could be promising to prepare self-assembled low-dimensional nanoarrays of metals and semiconductors with high yield.     

Investigation of synthesis and microstructure of bismuth titanates with TiO<Subscript>2</Subscript> rich compositions

Preliminary examinations regarding formation of bismuth titanates in a part of Bi₂O₃—TiO₂ system rich with TiO₂ have been carried out. Bismuth titanates have been synthesized from mixtures of Bi₂O₃ and TiO₂ (anatase) by the conventional solid-state method at the temperatures ranged from 1273 to 1473 K. Differential thermal analysis (DTA), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to study the formation of bismuth titanates. The following compounds have been achieved: Bi₄Ti₃O₁₂, Bi₂Ti₂O₇ and Bi₂Ti₄O₁₁. Existence of controversial bismuth titanate of formula Bi₂Ti₃O₉ in the Bi₂O₃—TiO₂ system has not been confirmed.     

A new bismuth potassium nitrate oxide, Bi1.7K0.9O2(NO3)2: Synthesis, structure, thermal behavior, and photocatalytic properties

We report here the first observation of a bismuth potassium nitrate Bi_1.7K_0.9O₂(NO₃)₂, obtained via thermal decomposition of bismuth and potassium nitrate mixtures. The new compound is orthorhombic, space group Immm (71), Z = 2, with a = 3.8698(7) Å, b = 3.8703(7) Å, and c = 24.1271(4) Å. Its crystal structure was refined from powder X-ray diffraction data by analogy with the mineral beyerite, Bi₂O₂Ca(CO₃)₂. The morphology and elemental composition of Bi_1.7K_0.9O₂(NO₃)₂ were characterized using scanning electron microscopy (SEM) with energy dispersive X-Ray spectroscopy (EDS). Its phase transformations upon heating and products of its thermal decomposition were studied using XRD, TGA and FTIR. At 440 °C, Bi_1.7K_0.9O₂(NO₃)₂ transforms to another basic bismuth potassium nitrate with demonstrates a very similar XRD pattern but slightly larger cell parameters. At 520 °C, the intermediate oxide nitrate decomposes into a mixture of crystalline α-Bi₂O₃ and KNO₃. The as prepared Bi_1.7K_0.9O₂(NO₃)₂ showed lower than TiO₂ (Degussa P25) photocatalytic activity upon decomposition of a widely used model pollutant, Rhodamine B (RhB) and photooxidation of potassium iodide under UV-vis light irradiation. Interaction with potassium iodide in alkaline media resulted in formation of Bi₅O₇I.     

In-Situ Hydrogen-Bond Tailoring To Construct Ultrathin Bi2O2O/Bi2O2(OH)(NO3) Nanosheets: Interactive CO2RR Promotion and Bismuth-Oxygen Moiety Preservation

Bismuth–oxygen moieties are beneficial for high-efficiency electrochemical CO₂ reduction (CO₂RR) to produce formate; however, preserving bismuth-oxygen moieties while applying a cathodic potential is challenging. This work reports the preparation of ultrathin Bi₂O₂O/Bi₂O₂(OH)(NO₃) nanosheets (BiON-uts) by in-situ tailoring of hydrogen bonds in a Bi₂O₂(OH)(NO₃) precursor. The BiON-uts exhibits a formate faradaic efficiency of 98 % with higher partial current density than that of most reported bismuth-based catalysts. Mechanistic studies demonstrate that the ultrathin nanosheet morphology facilitates ion-exchange between BiON-uts and the electrolyte to produce Bi₂O₂CO₃ as intermediate, and adsorption of CO₂ with surface Bi₂O₂O. DFT calculations reveal that the rate-limiting first electron transfer is effectively improved by the high electron affinity of Bi₂O₂CO₃. More importantly, high-efficiency CO₂RR in turn protects the bismuth–oxygen moieties from being reduced and thus helps to maintain the excellent CO₂RR activity. This work offers an interactive mechanism of CO₂RR promotion and bismuth–oxygen moiety preservation, opening up new opportunities for developing high-performance catalysts.