Bi Solubility Research Articles

Bismuth substitution at the strontium site in the magnetoplumbite-type Sr ferrite: Phase stability, structure, and magnetic properties

We report a phase diagram, structural and magnetic properties of magnetoplumbite-type (M-type) Sr1−xBixFe12O19 (0.0 ≤ x ≲ 0.3) synthesized under various oxygen potentials, pO2= 0–10 atm. A systematic composition analysis for single and polycrystalline samples reveals that Bi substitutes for the Sr site in SrFe12O19. Within a solubility limit of x ≈ 0.3, obtained by synthesis under pO2 = 0.01 atm, the Bi solubility is mostly determined by the reduction amount of Fe3+ to Fe2+ to compensate a charge imbalance. The Bi3+ doping results in lattice parameters, a and c, with trends different from those by La3+ doping, reflecting different spatial characters of La3+ and Bi3+ ions. However, a nearly identical linear decrease in the lattice-parameter ratio c/a indicates that Bi3+ can provide the function of La3+ in high-performance substituted M-type ferrites. The doping dependence of magnetic properties, particularly the saturation magnetization and the anisotropy field, are examined and compared between the Bi- and La-substituted cases.

Localized crystal imperfections coupled with phase diagram engineering yield high-performance rhombohedral GeTe thermoelectrics

Cubic β-GeTe alloys are apt to hoist the conversion efficiency for mid-temperature thermoelectric (TE) generators with their remarkably high peak figure-of-merit (zT) values at T > 700 K. Nevertheless, the TE device that consolidated by β-GeTe alloys have existed concerns as the rhombohedral α-GeTe to β-GeTe phase-transition leverage over the workability and thermal stability. Therefore, research efforts are redirected towards the high-performance α-GeTe, which stabilizes at a rhombohedral lattice below 700 K. By incorporating the maximal Bi solubility, the α-GeTe shows severe lattice distortion without forming the undesired impurities that affect the transport properties and deteriorate the thermal stability. The α-GeTe with high-dose Bi fulfills the counterbalance between low thermal conductivity κ and elevated power factor PF = S2ρ−1. Herein, the Bi0.1Ge0.9Te crystal attains the peak zT of 1.5 at 625 K and 1.9 at 713 K for its rhombohedral and cubic state, respectively. The Bi0.1Ge0.9Te features hierarchical twinning accompanied with dense stacking faults which explains its ultra-low lattice thermal conductivity κL in the temperature range of 300 K–700 K. The trade-off between incompatible low-κ and high-PF could be optimized via the phase diagram and defect engineering, which synergistically open a new category for TE performance advancement.

Improving the thermoelectric performance of Ti-doped NbFeSb by substitutional doping of the Sb atoms with the isoelectric and heavy Bi atoms

Solute Bi atoms in Nb0.8Ti0.2FeSb1−xBix samples scatter phonons and increase the effective mass, increasing the ZT within the Bi solubility limit; above this limit, concomitant Sb vacancies disproportionately donate holes, resulting in poor ZT.

Improvement of Bi doping in ZnO nanocrystals by co-doping with Al: crystal geometry calculations and photocatalytic activity

In this work we demonstrate enhancement in visible-light photocatalytic activity (PCA) of ZnO nanoparticles (NPs) with minimal attenuation of visible light transmittance. This approach can benefit numerous optoelectronic and photocatalytic applications. ZnO NPs were p-n co-doped with Al and Bi to improve Bi doping into the ZnO crystal. Al- and/or Bi-doped ZnO was coprecipitated by ammonia from aqueous nitrate solutions of Zn2+, Al3+, and Bi3+, followed by microwave heating. Doping concentrations in Al- and Bi- doped ZnO (AZO and BZO) and Al/Bi co-doped ZnO (ABZO) were 1, 3, 5, and 7 mole %. The resulting NPs were characterized by XRD, TEM, EDS, BET, and UV-visible absorption. While EDS shows that almost all added Bi was incorporated into the ZnO, XRD analysis of BZO reveals formation of α-Bi2O3 as a secondary phase due to the poor Bi solubility in ZnO. Co-doping of Al with Bi suppressed α-Bi2O3 formation and increased Bi solubility in ZnO. XRD-based calculations of the lattice constants and deformation strain, stress, and energy all show insertion of Al and/or Bi into the crystal with different extents according to the dopants’ solubilities into ZnO. AZO and BZO NPs had E g lowered by 0.05–1.39 eV and 0.30–0.70 eV, respectively, relative to ZnO. On the other hand, ABZO had E g reductions of only 0.01–0.20 eV due to formation of acceptor-donor complex through co-doping. ABZO gave higher PCA enhancements with respect to E g reductions (Δk photo/–ΔE g) than either AZO and BZO, with values up to 370, 126, and 13 min–1 eV–1, respectively.

Liquation phenomena in Sn/Bi2Te3, In/Bi2Te3 and Cu/Bi2Te3 couples

Bi2Te3-based materials are the most commonly used materials in commercial thermoelectric devices. There are many joints in thermoelectric devices, thus knowledge of interfacial reactions with Bi2Te3 substrate is important. Interfacial reactions are examined in the following couples, Sn/Bi2Te3 at 160 °C, In/Bi2Te3 at 140 °C and Cu/Bi2Te3 at 350 °C. The reaction temperatures are all lower than the melting points of the respective reaction substrates, so all these couples are solid/solid couples; however, liquation phenomena are observed in these couples. A reaction zone composed of two regions is formed in the Sn/Bi2Te3 couple reacted at 160 °C. The phase region adjacent to Sn is liquid phase and that adjacent to Bi2Te3 is SnTe with Bi solubility. The liquid phase is of near Bi-Sn eutectic composition and is formed due to alloying between Sn and Bi. The reaction path is Sn/liquid/SnTe/Bi2Te3. In the In/Bi2Te3 couple reacted at 140 °C, a liquid phase is formed among various reaction phases. The reaction path is In/In4Te3/liquid/Bi/(Bi2)m(Bi2Te3)n/Bi2Te3. Te atoms diffuse toward In and an In4Te3 phase is formed. Liquid phase is formed due to the alloying between In and remaining Bi. A metastable CuxBi2Te3, an oversaturated Bi2Te3 phase, is formed adjacent to the Bi2Te3 substrate in the Cu/Bi2Te3 couple reacted at 350 °C. The oversaturated phase decomposes, and a stable Cu2Te phase is formed. The remaining Bi adjacent to CuxBi2Te3 phase is molten at 350 °C, and the remaining Bi in contact with Cu, alloying with Cu and is also molten. Once the liquid phase is formed, the reaction rates become very fast. The reaction paths in the couples are illustrated with the proposed related phase equilibria isothermal sections.

Thermodynamic stability analysis of Bi-containing III-V quaternary alloys and the effect of epitaxial strain

The thermodynamic stability of Bi-containing III-V quaternary alloys was determined using the delta lattice parameter (DLP) model in conjunction with density functional theory (DFT) calculations. The DLP model and DFT-calculated enthalpy of mixing show remarkably good agreement for the In1-yGayAs1-xBix and GaAs1-x-yBixPy systems. Binodal and spinodal isotherm contours have been constructed for these systems, as well as In1-yGayP1-xBix, In1-yGaySb1-xBix, GaAs1-x-yBixSby, InAs1-x-yBixPy and InAs1-x-yBixSby, for their unstrained and pseudomorphically strained states as a function of lattice parameter. Enhanced Bi solubility can be achieved by epitaxial growth of alloys on substrates with lattice parameters from 0.565 to 0.6058 nm. The incorporation of an anion element with a smaller atomic size also increases the Bi solubility in the Bi low concentration regime. This work elucidates the thermodynamic stability dependence for Bi-containing quaternary alloys on choice of cation, anion and strain state. It also extends the DLP model to a wider composition range.

Bismuth Doping of Germanium Nanocrystals through Colloidal Chemistry

Nanogermanium is a material that has great potential for technological applications, and doped and alloyed Ge nanocrystals (NCs) are actively being considered. New alloys and compositions are possible in colloidal synthesis because the reactions are kinetically rather than thermodynamically controlled. Most of the Group V elements have been shown to be n-type dopants in Ge to increase carrier concentration; however, thermodynamically, Bi shows no solubility in crystalline Ge. Bi-doped Ge NCs were synthesized for the first time in a microwave-assisted solution route. The oleylamine capping ligand can be replaced by dodecanethiol without loss of Bi. A positive correlation between the lattice parameter and the concentration of Bi content (0.5–2.0 mol %) is shown via powder X-ray diffraction and selected area electron diffraction. X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), scanning TEM, and inductively coupled plasma–mass spectroscopy are consistent with the Bi solubility up to ...

Does Bi form clusters in GaAs1 − xBix alloys?

GaAs1 − xBix alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of small GaBi clusters incorporating As substitutional sites. However, the Ga vacancies should gather Bi atoms leading to small Bi clusters, and the Ga vacancies can act as nucleation centers for phase separation. The formation energy of the GaAs1 − xBix with respect to GaAs and GaBi shows a maximum at intermediate Bi concentrations. Thermodynamics and kinetics of the GaAs1 − xBix film growth is discussed. High Bi solubility is obtained, if the Bi atoms on the energetically favorable atom positions in the subsurface layer are relatively frozen. The Ga vacancy concentration may be increased by the incorporation of Bi. The Bi atoms can also prevent the out diffusion of Ga vacancies.

Ab initiostudy of the strain dependent thermodynamics of Bi doping in GaAs

The thermodynamics of Bi incorporation into bulk and epitaxial GaAs was studied using density functional theory (DFT) and anharmonic elasticity calculations. The equilibrium concentration of Bi was determined as a function of epitaxial strain state, temperature, and growth conditions. For a bulk, unstrained system, Bi in GaAs under typical growth conditions (Ga-rich and Bi-metal-rich at 400 \ifmmode^\circ\else\textdegree\fi{}C) has a dilute heat of solution of 572 meV/Bi and a solubility of $x=5.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ in GaAs${}_{1\ensuremath{-}x}$Bi${}_{x}$. However, epitaxial strain can greatly enhance this solubility, and under the same conditions an epitaxial film of GaAs${}_{1\ensuremath{-}x}$Bi${}_{x}$ with 5$%$ in-plane tensile strain is predicted to have a Bi solubility of $x=7.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, representing approximately a hundred times increase in solubility over the unstrained bulk case. Despite these potentially large increases in solubility, the equilibrium solubility is still very low compared to values that have been achieved experimentally through nonequilibrium growth. These values of solubility are also sensitive to the choice of the Bi reference state. If the primary route for phase separation is the formation of GaBi within the same structure, rather than Bi metal, GaBi would serve as the source/sink for Bi. If GaBi is used as the Bi reference state, the epitaxial formation energy on a bulk unstrained GaAs substrate is reduced dramatically to 144 meV/Bi, yielding a Bi solubility of $x=0.083$ in GaAs${}_{1\ensuremath{-}x}$Bi${}_{x}$. These calculations suggest that Bi solubility could be greatly enhanced if Bi metal formation is inhibited and the system is forced to remain constrained to the GaAs${}_{1\ensuremath{-}x}$Bi${}_{x}$ structure. Although GaBi is not a naturally stable compound, it could potentially be stabilized through a combination of kinetic limitations and alloying.

An X-Ray Diffraction and Thermogravimetric Study of Layered Perovskite Y1−xBixBaCo4O7

Layer-structured oxides Y1−xBixBaCo4O7 (0.00 ≤ x ≤ 0.05) were successfully synthesized and their structural and oxygen absorption properties were investigated by x-ray diffraction and thermogravimetry. Though Bi solubility was limited to about 5%, corresponding to Y0.95Bi0.05BaCo4O7, it is found that the structure and oxygen absorption properties of Y1−xBixBaCo4O7 are affected significantly as the Bi content x increases. Rietveld refinement results show that Y1−xBixBaCo4O7 (x ≤ 0.05) is single phase with a hexagonal crystal structure (space group P63zmc). Unit cell parameters and volume are changed and CoO4 tetrahedra are distorted along the c-axis in Bi doped YBaCo4O7. The TG results show that Y1−xBixBaCo4O7 undergoes two oxygen absorption processes in oxygen from room temperature to 1000°C and the maximum mass increase of the doped samples is less than that of YBaCo4O7. Bi doping effects on the structure and oxygen absorption properties are discussed on the basis of average radius and disorder of the Y site, the valence of Bi and the oxygen activation energy.

Bismuth solubility through binding by various organic compounds and naturally occurring soil organic matter

The present study was performed to examine the effects of soluble organic matter and pH on the solubility of Bi in relation to inference with the behavior of metallic Bi dispersed in soil and water environments using EDTA, citric acid, tartaric acid, l-cysteine, soil humic acids (HA), and dissolved organic matter (DOM) derived from the soil organic horizon. The solubility of Bi by citric acid, tartaric acid, l-cysteine, HA, and DOM showed pH dependence, while that by EDTA did not. Bi solubility by HA seemed to be related to the distribution of pKa (acid dissociation constant) values of acidic functional groups in their molecules. That is, HA extracted at pH 3.2 solubilized Bi preferentially in the acidic range, while HA extracted at pH 8.4 showed preferential solubilization at neutral and alkaline pH. This was related to the dissociation characteristics of functional groups, their binding capacity with Bi, and precipitation of Bi carbonate or hydroxides. In addition to the dissociation characteristics of functional groups, the unique structural configuration of the HA could also contribute to Bi-HA complex formation. The solubility of Bi by naturally occurring DOM derived from the soil organic horizon (Oi) and its pH dependence were different from those associated with HA and varied among tree species.

Experimental measurement of the solubility of bismuth phases in water vapor from 220°C to 300°C: Implications for ore formation

Abstract Preliminary measurements were carried out of the solubility of the O 2- buffering assemblage bismuth + bismite (Bi 2 O 3 ) in aqueous liquid–vapor and vapor-only systems at temperatures of 220, 250 and 300 °C. All experiments were carried out in Ti reaction vessels and were designed such that the Bi solids were contained in a silica tube that prevented contact with liquid water at any time during the experiment. Two blank (no Bi solids present) liquid–vapor experiments at 220 °C yielded Bi concentrations (±1 σ ) in the condensed liquid of 0.22 ± 0.02 mg/L, whereas the solubility measurements at this temperature yielded an average value of approximately 6 ± 9 mg/L, with replicate experiments ranging from 0.3 to 26 mg/L. Although the 6 mg/L value is associated with a considerable degree of uncertainty, the experiments do indicate transport of Bi through the vapor phase. Measured Bi concentrations in the condensed liquid at 250 °C were in the same range as those at 220 °C, whereas those at 300 °C were significantly lower (i.e., all below the blank value). Vapor-only experiments necessarily contained much smaller initial volumes of water, thereby making the results more susceptible to contamination. Single blank runs at 220 and 300 °C yielded Bi concentrations of 82 and 16 mg/L, respectively. Measured concentrations (±1 σ ) of Bi in the vapor-only solubility experiments at 220 °C were 235 ± 78 mg/L for an initial water volume of 0.5 mL, and at 300 °C were 56 ± 30 mg/L and 33 ± 21 for initial water volumes of 1 and 2 mL, respectively, suggesting strong preferential partitioning of Bi into the vapor. The results indicate a negative dependence of Bi solubility on temperature, but are inconclusive with respect to the dependence of Bi solubility on water density or fugacity. The experiments reported here suggest that significant Bi transport is possible in the vapor phase. Comparison of the liquid–vapor and vapor-only experiments further suggests that, at the conditions studied, the solubility of Bi in the vapor is significantly higher than that in the liquid phase (calculated distribution coefficients, i.e., C Vapor / C Liquid at 220 °C ranged from 81 to 168, where C is concentration in mg/L). The concentrations measured in the vapor-only experiments at 220 °C are approximately 11 orders of magnitude higher than those calculated from available thermodynamic data assuming no interaction between volatile Bi species and water molecules. This finding indicates that hydration of volatile Bi species probably occurs to a significant extent; similar to behavior observed previously in published vapor phase solubility studies of other metals. However, the interpretation of the results was complicated by the formation of Bi silicate phases and the lack of certainty that O 2 fugacity buffering was effective throughout the experiments.

Bismuth redistribution induced by intermetallic compound growth in SnBi/Cu microelectronic interconnect

It was found that Bi particles, with a diameter of 100 nm, precipitated along Cu3Sn/Cu interface and Bi crystallites dispersed in Cu3Sn layer in 42Sn58Bi/Cu microelectronic interconnect, when it was aged at 120 °C for 7 days. The mechanism for Bi redistribution like this was discussed. Cu6Sn5 turned into Cu3Sn by Cu diffusion that is dominant in Sn/Cu inter-diffusion during the aging process. Bi precipitation occurred in Cu3Sn due to lower Bi solubility in Cu3Sn than that in Cu6Sn5. The Bi precipitates can traverse the formed Cu3Sn quickly toward the Cu3Sn/Cu interface, attributed to the Kirkendall effect. They stayed and nucleated there to form particles, owing to their unwettability on Cu. The formed Cu3Sn got oversaturated with Bi, when the joint cooled from 120 °C to room temperature. Then Bi crystallites precipitated dispersedly in Cu3Sn layer.

Bi incorporation in GaN andAlxGa1−xNalloys

Bismuth has been recently suggested as a possible surfactant in the growth of GaN samples in place of As and Sb. In this work we use a density-functional first-principles technique to investigate the solubility and electrical activity of Bi impurities in GaN and AlGaN, two key parameters for surfactants that are so far unknown for bismuth. We find that the Bi solubility in GaN and AlGaN is very low. In n-type and moderate p-type conditions Bi behaves like a donor or an isoelectronic impurity substituting Ga at the cation site, while in extreme p-type conditions a multiple-donor ${\mathrm{Bi}}_{\mathrm{N}}$ defect is formed that hinders efficient p-type doping. In AlGaN, Al and Bi substitutional defects show a tendency to pair, giving origin to an Al-Bi complex, whose electronic properties are similar to those of an isolated ${\mathrm{Bi}}_{\mathrm{Ga}}$ impurity. The results of our investigations suggest that the use of Bi as surfactant is incompatible with an efficient p-type doping. Finally we examine the features of the defects extrinsic levels, identifying the current data on Bi-doped GaN luminescence as a conduction-band--to--donor recombination process for the ${\mathrm{Bi}}_{\mathrm{Ga}}$ defect.

High concentration Bi δ-doping layers on Si(001)

Medium energy ion scattering, X-ray standing waves and measurements of crystal truncation rods were used to show that it is possible to prepare spatially well confined Bi doping layers (δ-doping layers) on Si(001) with a Bi doping level of 3 × 1021cm−3 by a combination of Bi molecular beam epitaxy and low temperature deposition of a Si top layer with subsequent annealing (solid phase epitaxy). The Bi concentration exceeds the equilibrium Bi solubility by more than three orders of magnitude. The Bi atoms are incorporated into the Si host lattice on substitutional sites. The Bi doping profile exponentially decays into the top Si layer with an attenuation length ranging from 40 to 6Åand a fraction of Bi atoms in substitutional lattice sites of up to 96%, depending on the annealing conditions.

The Ag-Bi (Silver-Bismuth) System

The solid solubility of Bi in (Ag) was estimated to be -3 at.% on the basis of X-ray work [31Bro]. Lattice parameter measurements of alloys at the temperature extremes of 200 and 259 ~ yielded solubilities of 0.312 and 0.784 at.% B i, respectively [40Chi]. More extensive studies of Bi solubility involving both micrographic and lattice parameter measurements between 266 and 900 ~ were conducted by [46Rau]. Bi solubility in (Ag) was studied by thermoelectric power and lattice parameter measurements over the temperature range 300 to 900 ~ [75Gla, 83Ako]. Recently, electron probe microanalysis (EPMA) of the Ag-rich phase quenched from 650 to 925 ~ in the two-phase region was reported [88Sch]. The solidus and solvus lines for the Ag side recommended in this evaluation are compared with all of the foregoing reported data in Fig. 3. The solidus line through the data points is based mainly on estimated thermodynamic data for the Ag solid solution. This is discussed in the "Thermodynamics" section. The projected solubility of Bi at 30 ~ is 0.004 at.%. On this basis, it appears that the solubility of 0.16 at.% reported by thermoelectric power measurement by [67Poi] at 30 ~ is excessive.

Ultra-low temperature OMVPE of InAs and InAsBi

InAs and InAsBi have been grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE) over a broad temperature range from 600 to as low as 275° C. This is the lowest growth temperature ever reported for conventional OMVPE. It is demonstrated that lowering the growth temperature is the most effective approach for increasing the maximum Bi content in InAsBi alloys where the Bi solubility limit is 0.025 at.%. For example, InAsBi samples with Bi concentrations as high as 6.1 at.% have been successfully grown at a temperature of 275° C. Trimethylindium, arsine, and trimethylbismuth were used as precursors for most experiments. The growth efficiency is a constant for temperatures above 400° C, indicating that the growth rate is diffusion limited. For lower temperatures, it decreases exponentially with decreasing temperature with an activation energy of 24 kcal/mol. Incomplete pyrolysis of TMIn limits the growth rate in this temperature regime. By substituting ethyldimethylindium for TMIn the growth rate can be increased at lower temperatures. Hall effect measurements show that then-type background concentration increases from approximately 2.3 × 1016 to 1019 cm−3 as the growth temperature decreases from 600 to 325° C. Secondary ion mass spectroscopy results show that the dominant impurity is carbon. Thus, carbon is mainly a donor in these materials. The integrated photoluminescence intensity drops rapidly with decreasing growth temperature.