Bi Fraction Research Articles

Microstructure and mechanical properties of Sn–xBi solder alloy

In this study, microstructure and mechanical properties of Sn–xBi solder alloy were investigated. In Sn–3.6Bi and Sn–7.25Bi solder alloys, the particle-shaped Bi phase distributed in Sn-rich phase matrix. In Sn–14.5Bi and Sn–29Bi solder alloys, the shape of Bi phase was irregular. In Sn–58Bi solder alloy, the island-shaped Sn-rich phase distributed in Bi phase uniformly. The hardness of Sn–xBi was improved from 11.36 to 27.04 MPa first and declined to 10.05 MPa then when the Bi fraction was increased form 0 to 100 wt%. The bend fracture energy of Sn–58Bi showed a dependence on the loading speed. Moreover, the bend fracture energy of Sn–29Bi solder alloy was lower than that of Sn–14.5Bi and Sn–58Bi, which was caused by the special microstructure of Sn–29Bi.

Sedimentary trace-element records of natural and human-induced environmental changes in the East China Sea

Total and chemical fractions of nine potential harmful elements (V, Cr, Co, Ni, Cu, Zn, Cd, Pb and Bi) and five lithogenic elements (Li, Sc, Rb, Cs and Th) in two Pb-210-dated cores from the East China Sea were analyzed to investigate their applications in paleoenvironment studies, and to reconstruct the histories of environmental changes. The residual fraction was the largest pool of trace elements in sediments. Potential harmful elements exhibited distributions that were similar to residual fractions and the lithogenic elements, indicating their terrestrial origin mainly derived from the Changjiang River and the old Huanghe delta. In the coastal core, the distributions of total and residual trace elements recorded the dry/wet variations of the Changjiang runoff since the 1850s. Total potential harmful elements and lithogenic elements in the offshore core reflected fluctuations in the strength of the Jiangsu coastal current and the East Asia Winter Monsoon over the last century. The response mechanisms of sedimentary trace elements to the runoff and monsoon variations involved direct terrestrial input of elements and the impacts of TOC and sediment grain size on trace elements in sediments. Enrichment factors (EFs), chemical fractions and principal component analysis (PCA) were used to evaluate the anthropogenic disturbance on potential harmful elements. PCA identified the lithogenic fraction of trace elements in both cores and the anthropogenic/authigenic input in the coastal core. Increases of the EFs and labile fractions of Zn, Pb and Bi in upper sediments of the coastal core indicated increased anthropogenic input of Zn and Pb since the 1980s, and increased Bi input since the 1940s. Increases in oxidizable Co, Ni, Cu, Zn, Pb and Bi above 16 cm were related to eutrophication and elevated marine organic matter in inshore East China Sea after the 1990s. Sediment records in offshore did not show any evidence of anthropogenic influence on the potential harmful elements. This study revealed that trace elements in sediments were good proxies for natural and human-induced environmental changes in waters.

Influence of Pb(BO2)2 Doping on Superconducting Properties of (Bi,Pb)-2223 HTS

The effect of lead borate Pb(BO2)2 doping on the phase formation and superconducting properties of (Bi,Pb)-2223 high-temperature superconductivity (HTS) has been studied. Samples with nominal composition Bi1.7Pb0.3−xSr2Ca2Cu3Oy [Pb(BO2)2]x, x = 0–0.3, were prepared by the standard solid-state processing. The appropriate mixtures were calcined at 850 °C for 30 h. The resulting materials were pressed into pellets and annealed at 840 °C for 30 h in air. X-ray diffraction, resistivity, and critical current density measurements were performed on the undoped (reference) and Pb(BO2)2-doped (Bi,Pb)-2223 compounds. The dominance of the low-Tc 2212 phase over the high-Tc 2223 phase was observed in the reference sample. With the increasing of doping level, the 2223 phase is significantly enhanced and its increase is associated with the decrease of the 2212 phase. Our results show that the sample with x = 0.075 is the best in the present study. The calculated volume fraction of (Bi,Pb)-2223 phase increases from ∼25 % for reference specimen to ∼85 % for x = 0.075 in a short sintering time (60 h). The (Bi,Pb)-2223 sample with x = 0.075 (0.15 wt% boron) reveals significant enhancement of critical current density (from 25 up to 360 A/cm2) compared to the reference sample. Obtained results could enable us to develop an accelerated and simple method for producing a high purity (Bi,Pb)-2223 superconducting materials by a proper amount of Pb(BO2)2 doping.

Use of INAA and ICP-MS for the assessment of trace element mass fractions in adult and geriatric prostate

The variation with age of the mass fraction of 54 trace elements (Ag, Al, As, Au, B, Be, Bi, Br, Cd, Ce, Co, Cr, Cs, Dy, Er, Eu, Fe, Ga, Gd, Hf, Hg, Ho, Ir, La, Li, Lu, Mn, Mo, Nb, Nd, Ni, Pb, Pd, Pr, Pt, Rb, Re, Sb, Sc, Se, Sm, Sn, Ta, Tb, Te, Th, Ti, Tl, Tm, U, Y, Yb, Zn, and Zr) in intact nonhyperplastic prostate of 65 healthy 21–87 year old males was investigated by instrumental neutron activation analysis with high resolution spectrometry of long-lived radionuclides and inductively coupled plasma mass spectrometry. This work revealed that there is a significant tendency for an increase in Bi, Cd, Co, Fe, Hg, Sc, Sn, Th, U, and Zn (p < 0.0014) mass fraction in normal prostate from age 21 years to the sixth decade. In the sixth to ninth decades the mass fractions of almost all chemical elements investigated in nonhyperplastic prostates were maintained at approximately stable levels. Our finding of correlation between pairs of prostatic chemical element mass fractions indicates that there is a great disturbance of prostatic chemical element relationships with increasing age.

Atomistic tight-binding study of electronic structure and interband optical transitions in GaBixAs1−x/GaAs quantum wells

Large-supercell tight-binding calculations are presented for GaBixAs1−x/GaAs single quantum wells (QWs) with Bi fractions x of 3.125% and 12.5%. Our results highlight significant distortion of the valence band states due to the alloy disorder. A large full-width-half-maximum (FWHM) is estimated in the ground state interband transition energy (≈33 meV) at 3.125% Bi, consistent with recent photovoltage measurements for similar Bi compositions. Additionally, the alloy disorder effects are predicted to become more pronounced as the QW width is increased. However, they are less strong at the higher Bi composition (12.5%) required for the design of temperature-stable lasers, with a calculated FWHM of ≈23.5 meV at x = 12.5%.

Preparation and electrode properties of composite cathodes based on Bi1−xSrxFeO3−δ with Perovskite-type structure

Abstract Various volume fractions of perovskite-type Bi 0.5 Sr 0.5 FeO 3 − δ (BSF55) and double perovskite PrBaCo 2 O 5+δ (PBCO) composite cathodes were prepared. The chemical compatibility of BSF55–PBCO composite material was confirmed by the absence of a secondary phase after firing below 850 °C for 2 h and annealing below 700 °C for 100 h. The electrode resistance of composite cathodes is indicated by Nyquist plots, all consisting of one arc in the high frequency (HF) range and another in the low frequency (LF) range. At 450 and 500 °C, the resistance in the HF range decreased linearly as the PBCO fraction increased, while BP73 showed the smallest arcs in the LF range. The activation energy of electrode resistance clearly decreased with the addition of up to 30 vol.% PBCO. This implies the mechanism of the oxygen reduction reaction underwent some changes due to the added PBCO. Considering the activation energy of the electrode resistance and the P(O 2 ) dependence of resistance at 700 °C, the addition of PBCO to BSF55 was shown to affect not only the mechanism but also the rate-determining step of oxygen reduction.

Optimization of the heavy metal (Bi-W-Gd-Sb) concentrations in the elastomeric shields for computer tomography (CT).

Eight elastomeric composites (NRU, GR1–GR4, NRBG08–NRBG24) containing mixtures of different proportions of heavy metal additives (Bi, W, Gd and Sb) have been synthesized and examined as protective shields. The NRU sample was a pure rubber matrix and served as a reference sample for heavy metal modified composites. Experimental procedure used for evaluation of the composite shields and their attenuation properties was based on the utilization of HPGe spectrometry and analysis of X-ray fluorescence radiation intensity of the heavy metal additives in the following energy ranges for: Sb (20–35 keV), Gd (35–55 keV), W (55–70 keV) and Bi (70–90 keV). The main contributor to the induced X-ray fluorescence radiation within the shield is Bi additive and the intensity of the X-ray radiation generated within the energy range of 70–90 keV strongly depends on its concentration. It was found that decreasing concentration of the Bi fraction from 0.35 (GR samples) to 0.15 (NRBG samples) results in significant lowering Bi X-ray fluorescence radiation within the 70–90 keV energy range. Secondary effect of decreasing Bi concentration was efficient diminishing excitation processes for lower Z heavy metal additives (W, Gd and Sb, GR vs. NRBG samples). As the final quality parameter of the shielding properties for the examined elastomers, dose reduction factor (DRF) coefficients were calculated for each shield. It was found, that the best shielding properties are observed for composites with lower Bi concentration (0.15 vs. 0.35 Bi mass fraction) with only slight further improvement of their parameters (DRF) with increasing of Gd concentration (Gd mass fraction 0.08, 0.16 and 0.24). The most efficient dose reduction composite was found to be NRBG24 elastomer with DRF value 0.47 (53 % dose reduction) for ca. 2 mm and 0.44 g/cm2 layer thickness.

Raman scattering studies of strain effects in (100) and (311)B GaAs1−xBix epitaxial layers

We report room-temperature Raman studies of strained (100) and (311)B GaAs1−xBix epitaxial layers for x ≤ 0.039. The Raman spectra exhibit a two-mode behavior, as well as disorder-activated GaAs-like phonons. The experimental results show that the GaAs-like LO(Γ) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs (∼293 cm−1) with the alloyed Bi fraction x and the introduced in-plane lattice strain ε∥, by ΔωLO=Δωalloy−Δωstrain. X-ray diffraction measurements are used to determine x and ε∥ allowing Δωalloy to be decoupled and is estimated to be −12(±4) cm−1/x for (100) GaAs1−xBix. ΔωLO is measured to be roughly double for samples grown on (311)B-oriented substrates to that of (100) GaAs. This large difference in redshift is accounted for by examining the Bi induced strain, effects from alloying, and defects formed during high-index (311)B crystal growth.

Electromechanical strain and bipolar fatigue in Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 ceramics

Lead-free ceramics of composition Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 were prepared using solid state synthesis techniques. The dielectric spectra showed a Tmax of more than 320 °C for all compositions, and the transitions became increasingly diffuse as the Bi(Mg1/2Ti1/2)O3 content increased. A lower temperature transition, indicating a transformation from an ergodic to a non-ergodic relaxor state, was also seen for all compositions, and this transition temperature decreased as the mole fraction of Bi(Mg1/2Ti1/2)O3 increased. The composition with 1% Bi(Mg1/2Ti1/2)O3 showed characteristic ferroelectric-like polarization and strain hysteresis. However, compositions with increased Bi(Mg1/2Ti1/2)O3 content became increasingly ergodic at room temperature with pinched polarization loops and no negative strain. Among these compositions, the magnitude of d33* increased with Bi(Mg1/2Ti1/2)O3 content, and the composition with 10% Bi(Mg1/2Ti1/2)O3 exhibited a d33* of 422 pm/V. Fatigue measurements were conducted on all compositions and while the 1% Bi(Mg1/2Ti1/2)O3 composition exhibited a measurable, but small loss in maximum strain after a million cycles; all the other compositions from 2.5% to 10% Bi(Mg1/2Ti1/2)O3 were essentially fatigue-free. Lastly, optical and alternating current impedance measurements were employed to identify intrinsic conduction as the dominant conduction mechanism. These compositions were also highly insulating with high resistivities (∼107 Ω-cm) at high temperatures (440 °C).

Effect of Fe2O3 Nano-Oxide Addition on the Superconducting Properties of the (Bi,Pb)-2223 Phase

The effect of different weight percentages of nano-Fe2O3 on the properties of Bi1.8Pb0⋅4Sr2Ca2Cu3O10+δ superconducting phase was studied. Phase formation, elemental real contents and granular microstructure of the investigated samples were carried out using X-Ray powder Diffraction (XRD), Energy Dispersive X-ray emission (EDX), Proton Induced X-ray Emission (PIXE), Rutherford Backscattering Spectrometry (RBS) and Scanning Electron Microscopy (SEM). XRD data indicated that the volume fraction of (Bi,Pb)-2223 decreased as nano-Fe2O3 wt.% increased. PIXE and EDX analyses showed that the PIXE technique is more accurate for detecting the nano-Fe2O3 than the EDX technique. The oxygen content, determined from RBS, decreased as nano-Fe2O3 wt.% increased. The superconducting properties of the prepared samples were investigated using electrical resistivity and I–V curves, at 77 K, measurements. It was found that the granular structure and the critical current density were improved up to 0.2 wt.% of nano-Fe2O3 addition. The superconducting transition temperature T c decreased as nano-Fe2O3 wt.% increased, attributing this to the decrease of the volume fraction or trapping of mobile holes. The enhancement rate of J c for (Bi,Pb)-2223 phase added with nano-Fe2O3 is 9 %, which is lower than that of (Bi,Pb)-2223 phase added with SnO2, Ag2O, Al2O3 and MgO. This means that the nano-magnetic addition has the lowest enhancement rate in both J c and T c.

Thermoelectric properties of Bi-added Co4Sb12 skutterudites

Void filling in (I) Bix-added Co4Sb12 or (II) Sb/Bi substitution of Co4Sb12−xBix has been investigated for structural and thermoelectric properties evaluation. X-ray powder data Rietveld refinements combined with electron probe microanalyses showed a polycrystalline and practically Bi-free CoSb3 skutterudite phase as the major constituent as well as a secondary Bi phase in the grain boundaries. For series I alloys, the electrical conductivity, Seebeck coefficient and thermal conductivity were measured as a function of temperature in the range from 450 to 750 K. The electrical conductivity of all the samples increased with increasing temperature, showing a semiconducting nature with smaller values of the Seebeck coefficient for higher Bi fractions. Conduction over the entire temperature range was found to arise from a single p-type carrier. Thermal conductivity showed a reduction with Bi added in all the samples, except for Bi0.75Co4Sb12, and the lowest lattice thermal conductivity was found for a Bi-added fraction of 0.5. The maximum zT value of 0.53 at 632 K is higher than that of Co4Sb12.

MOVPE growth of Ga(AsBi)/GaAs multi quantum well structures

This paper summarizes results of the epitaxial growth of Ga(AsBi) by metal organic vapor phase epitaxy (MOVPE) using all-liquid group V precursors. Ga(AsBi)/GaAs multi quantum well (MQW) samples are grown on GaAs (001) substrates at temperatures as low as 375°C and 400°C using triethylgallium (TEGa), tertiarybutylarsine (TBAs) and trimethylbismuth (TMBi) as precursors. High resolution x-ray diffraction (HR-XRD), transmission electron microscopy (TEM) as well as atomic force microscopy (AFM) measurements show that MQW structures with good crystalline quality are realized. Under specific growth conditions, the Bi droplet formation can be avoided completely. The incorporated Bi-content is limited depending on the growth temperature used. Surplus Bi segregates at the surface and incorporates into the subsequent GaAs barrier when the Bi supply is stopped. The MQW samples show room temperature photoluminescence (PL) already after growth. A redshift and a decreasing PL signal intensity with increasing Bi fraction is observed.

The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing

The GaBixAs1−x bismide III-V semiconductor system remains a relatively underexplored alloy particularly with regards to its detailed electronic band structure. Of particular importance to understanding the physics of this system is how the bandgap energy Eg and spin-orbit splitting energy Δo vary relative to one another as a function of Bi content, since in this alloy it becomes possible for Δo to exceed Eg for higher Bi fractions, which occurrence would have important implications for minimising non-radiative Auger recombination losses in such structures. However, this situation had not so far been realised in this system. Here, we study a set of epitaxial layers of GaBixAs1−x (2.3% ≤ x ≤ 10.4%), of thickness 30–40 nm, grown compressively strained onto GaAs (100) substrates. Using room temperature photomodulated reflectance, we observe a reduction in Eg, together with an increase in Δo, with increasing Bi content. In these strained samples, it is found that the transition energy between the conduction and heavy-hole valence band edges is equal with that between the heavy-hole and spin-orbit split-off valence band edges at ∼9.0 ± 0.2% Bi. Furthermore, we observe that the strained valence band heavy-hole/light-hole splitting increases with Bi fraction at a rate of ∼15 (±1) meV/Bi%, from which we are able to deduce the shear deformation potential. By application of an iterative strain theory, we decouple the strain effects from our experimental measurements and deduce Eg and Δo of free standing GaBiAs; we find that Δo indeed does come into resonance with Eg at ∼10.5 ± 0.2% Bi. We also conclude that the conduction/valence band alignment of dilute-Bi GaBiAs on GaAs is most likely to be type-I.

Structural morphologies of Cu–Sn–Bi immiscible alloys with varied compositions

The macroscopic morphology of Cu–Sn–Bi immiscible alloys with compositions varying from hypomonotectic, monotectic to hypermonotectic alloys was experimentally investigated by conventional casting method. It is shown that the hypomonotectic and monotectic alloys present a core–shell morphology composed of Bi-rich core and CuSn-rich shell. In contrast, the hypermonotectic alloys, as the fraction of Bi increased, transform from a triple-layer morphology, a core–shell morphology with CuSn-rich core and Bi-rich shell, to a uniform morphology with fine CuSn-rich phase dispersing in Bi-rich matrix. Besides, the effect of velocity of solidification front on formation of core–shell morphology for the critical composition in hypermonotectic alloys was studied by casting molten alloy into molds with different radii. The relation between the volume fraction of two immiscible liquid phases and morphology was clarified for hypermonotectic alloys. The solidification paths of alloys under all compositions were discussed.

Graphene growth on a Pt(111) substrate by surface segregation and precipitation

We report on the fabrication of a sizable graphene sheet on a carbon-doped Pt(111) substrate through surface segregation and precipitation. Scanning Auger electron spectroscopy (AES) reveals that the graphene covered more than 98% of the substrate surface. Our graphene consists of single-layer graphene across the substrate with fractions of several micrometer wide bi- and tri-layer graphene islands. We also show that the number of graphene layers can be precisely determined by analyzing AES data. While Raman spectroscopy is usually used to study graphene on SiO2, we show that AES is a powerful tool to characterize graphene grown on metal substrates.

Non-stoichiometric GaAsBi/GaAs (100) molecular beam epitaxy growth

The growth of III–V bismuthides is complicated by the low incorporation efficiency of Bi in GaAs, leading either to the formation of metallic Bi droplets or low layer composition fractions. Typically growth is performed between 280 and 350 °C and at near stoichiometric Ga:As fluxes in order to encourage Bi incorporation. However most work reported to date also utilises As 2 as the As overpressure constituent. It is found in this work that growth with As 4 allows high Bi composition films with the standard 1:20 Ga:As 4 beam equivalent pressure ratio (BEPR) utilised for higher temperature buffer layer growth. The Bi fraction versus Bi:As 4 BEPR is found to be initially linear, until a maximum value is obtained for a given temperature after which the continued oversupply of Bi results in the formation of droplets.

GaAsBi atomic surface order and interfacial roughness observed by STM and TEM

GaAsBi is an interesting ternary material for opto-electronic applications. Bi fractions of 11-13% allow 1.55 μm emissions from a range of bulk and QW structures. GaAsBi has shown strong room temperature photoluminescence. The temperature insensitive band gap and large spin orbit splitting are attractive optoelectronic features, however the typical full width half maximum is 2.5 times greater than GaAs. In solid source molecular beam epitaxy (MBE), near stoichiometric fluxes and low growth temperatures are necessary to achieve the desired Bi content. In order to explore photoluminescence linewidth broadening and the accommodation of strain a joint scanning tunnelling microscopy (STM) and scanning transmission electron microscopy (STEM) study of quasi-bulk and QW structures has been undertaken.

Coprecipitation of barium-bismuth fluorides from aqueous solutions: Nanochemical effects

The BaF2-BiF3 system was studied by the method of coprecipitation from aqueous solutions. The region of precipitation of single-phase nonoxygen powders was revealed (the atomic fraction of Bi in the initial solution was 0.35–0.43). The composition of the cubic fluorite-type phase is BaBiF5 according to an energy-dispersive X-ray spectroscopy analysis. Samples prepared from solutions with high Bi concentrations contain oxygen. This indicates that the hydrolysis temperature of BiF3 decreases when compared with that of the bulk samples and that this process takes place at room temperature. The coherent intergrowth of nanoparticles with the formation of single crystals with nonfaceted complex forms was shown by scanning electron microscopy and transmission electron microscopy.

Deep level defects in GaAs1−xBix/GaAs heterostructures

Deep level transient spectroscopy (DLTS) measurements were performed on p–i–n diodes having i-regions that include a GaAs1−xBix layer sandwiched between two GaAs layers, all grown at T < 400 °C. A GaAs1−xBix/GaAs heterostructure with Bi fraction x = 4.7% grown at 285 °C was found to have several traps in concentrations of ∼5 × 1015 cm−3. The location of the observed traps in the i-region is determined from simulations of the band diagrams of these devices at the bias conditions used for the DLTS measurements and confirmed by DLTS spectra taken at various filling voltages.

From crystal to amorphous: A novel route to unjamming in soft disk packings

Numerical studies on the unjamming packing fraction of bi- and polydisperse disk packings, which are generated through compression of a monodisperse crystal, are presented. In bidisperse systems, a fraction f(+) = 0.400 up to 0.800 of the total number of particles has their radii increased by [Formula: see text] R , while the rest has their radii decreased by the same amount. Polydisperse packings are prepared by changing all particle radii according to a uniform distribution in the range [-ΔR, ΔR] . The results indicate that the critical packing fraction is never larger than the value for the initial monodisperse crystal, Φ(o) = π/√12, and that the lowest value achieved is approximately the one for random close packing. These results are seen as a consequence of the interplay between the increase in small-small particle contacts and the local crystalline order provided by the large-large particle contacts.