Increasing Bi Content Research Articles

Preparation, microstructure and thermal properties of Mg[sbnd]Bi alloys as phase change materials for thermal energy storage

Comparing with Al-based phase change material, Mg-based phase change material is getting more and more attention due to its high corrosion resistance with encapsulation materials based on iron. This study focuses on the characterization of Mg36%Bi, Mg54%Bi and Mg60%Bi (wt. %) alloys as phase change materials for thermal energy storage at high temperature. The phase compositions, microstructure and phase change temperatures were investigated by X-ray diffusion (XRD), electron probe micro-analysis (EPMA) and differential scanning calorimeter (DSC) analysis, respectively. The results indicates that the microstructure of Mg36%Bi and Mg54%Bi alloys are mainly composed of α-Mg matrix and α-Mg + Mg3Bi2 eutectic phases, Mg60%Bi alloy are mainly composed of the Mg3Bi2 phase and α-MgMg3Bi2 eutectic phases. The melting enthalpies of Mg36%Bi, Mg54%Bi and Mg60%Bi alloys are 138.2, 180.5 and 48.7 J/g, with the phase change temperatures of 547.6, 546.3 and 548.1 °C, respectively. The Mg54%Bi alloy has the highest melting enthalpy in three alloys. The main reason may be that it has more proportion of α-Mg + Mg3Bi2 eutectic phases. The thermal expansion of three alloys increases with increasing temperature. The values of the thermal conductivity decrease with increasing Bi content. Besides, the activation energy of Mg54%Bi was calculated by multiple DSC technology.

Pressure and composition dependence of structural, electronic and optical properties of GaAsBi alloys

In this work, we have investigated the structural, electronic and optical properties of zinc-blende (ZB) GaAs1−xBix ternary alloys at normal and under hydrostatic pressure. Firstly, we have performed the calculation of the structural and electronic properties of binary compounds GaAs and GaBi and for GaAs1−xBix ternary alloy at different compositions x=0.0625, 0.125, 0.25, 0.5 and 0.75. It is observed that lattice parameter increases with increasing Bi content; however the direct band gap EgΓ-Γ of GaAsBi decreases non-linearly. We have studied the variation of the spin–orbit splitting energy Δso with respect of Bi compositions. Our study shows that the Δso exceeds the energy gap Eg for bismuth fractions greater than 15%. We have also studied the effect of hydrostatic pressure on the structural, electronic and optical properties of the GaAs0.9375Bi0.0625, GaAs0.875Bi0.125 and GaAs0.75Bi0.25. We found that the application of hydrostatic pressure leads to variation of the electronic and optical properties of these materials.

Ab-initio DFT FP-LAPW GGA and LDA TB-mBJ and SO theoretical study of structural and elastic properties of Zinc-Blende crystal phase GaAs1−xBix alloys

We present an ab-initio theoretical study of structural and elastic properties of GaAs1−xBix alloys in the Zinc-Blende (ZB) phase. We use a recent version of Wien2k package code based on Density Functional Theory (DFT) Full Potential and Linearized Augmented Plane Waves (FP-LAPW) method including recent Tran-Blaha modified Becke–Johnson correction of the exchange potential (TB-mBJ) and the spin–orbit interaction (SO). The calculations are performed within the Local Density Approximation (LDA) as well as the Generalized Gradient Approximation (GGA). We study first the structural properties of GaAs1−xBix alloys by solving Murnaghan equation of state. Our results show that the ZB phase is the lowest equilibrium crystal structure of GaAs1−xBix in the whole alloy composition range, in agreement with previous theoretical predictions. The variations versus Bi contents of the ZB GaAs1−xBix lattice constant a0, bulk modulus B0 and its pressure derivative B0′ are also found very close to other theoretical and experimental data, but with much smaller bowing effects indicating a better resolution thanks to TB-mBJ correction. The variations of B0 versus the reverse equilibrium volume of the unit cell (1/V0) are found to be described by the simple linear empirical expression B0 = −0.21068 + 0.16695/V0 which is close to the theoretical prediction for III-V semiconductors with, however, somewhat lower linear coefficients values, suggesting a more metallic behavior. In a second part of this work, we use Birch–Murnaghan approach to study the elastic properties of GaAs1-xBix alloys. The elastic stiffness coefficients, C11, C12 and C44, and their variations versus alloy composition were determined for ZB GaAs1−xBix alloy. Their values in GaAs and GaBi binary compounds are found in very good agreement with available experimental and/or theoretical data. Their variations in GaAs1−xBix alloy show a monotonic decrease with increasing Bi contents, indicating a softening behavior as is typically the case for metallic alloys. The values of the bulk modulus derived with the help of C11, C12 and C44 elastic stiffness coefficients are found very close to B0 values derived directly from Murnaghan equation of state, indicating the good accuracy of Cij coefficients deduced from Birch–Murnaghan procedure.

Synthesis and characterization of Bi x (Se80Te20)100−x amorphous thin films

In this study, amorphous Bi x (Se80Te20)100−x glasses with (0 ≤ x ≤ 12) were prepared by the usual melt quench technique. Thin films of these glasses were deposited onto glass substrates by using thermal evaporation method. The amorphous nature of the as-prepared films was confirmed by X-ray diffraction. Structural investigations were performed using X-ray energy-dispersive spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The transmission spectra of these films were measured at normal incidence in the wavelength range 400–2500 nm. Swanepoel’s analysis of the maxima and minima of the interference fringes was used to determine the film thickness, the complex index of refraction and the extinction coefficient with high accuracy. The dispersion of the refractive index was well discussed in terms of the single oscillator model (Wemple and DiDomenico). It was found that increasing Bi content led to the increase in refractive index and the extinction coefficient of the Bi x (Se80Te20)100−x films, while the optical band gap decreased. The mechanism of the optical absorption in Bi x (Se80Te20)100−x films obeyed the allowed indirect optical transition. The decrease in optical gap with increasing Bi content was discussed in terms of the chemical bond approach.

Structural, magnetic and electrical properties of Bi doped LaFeO3 nano-crystals, synthesized by auto-combustion method

La1−xBixFeO3; 0 ≤ x ≤ 0.2 have been prepared by citrate auto-combustion method. The results of X-ray diffraction showed that LaFeO3 has single phase with orthorhombic structure. With increasing Bi content, traces of secondary phase of rhombohedral structure are observed. The transmission electron microscope showed that the prepared compositions have nanocrystalline structure with an increase of the particle size increases with increasing Bi content. The magnetic properties of the samples were investigated by vibrating sample magnetometer, in which saturation magnetization (Ms) and coercivity (Hc) were determined. The value of Ms increases with increasing Bi content up to x = 0.10, while Hc decreases with increasing Bi content. The temperature dependence of dielectric constant, dielectric loss and ac conductivity at different frequencies (100 kHz–5 MHz) were studied.

Effect of Trivalent Bi Doping on the Seebeck Coefficient and Electrical Resistivity of Ca3Co4O9

We present the effects of trivalent Bi doping on the microstructure and thermoelectric (TE) properties of Ca3Co4O9 (Ca-349). Specimens were prepared by spark plasma sintering (SPS). The lattice parameters of the conducting [CoO2] layer and insulating [Ca2CoO3] layer of Ca-349 were determined using Rietveld refinements of x-ray diffraction (XRD) data. Partial substitution of Bi for Ca did not lead to any change in the misfit ratio of the conducting versus insulating layers. XRD and transmission electron microscopy (TEM)/energy-dispersive spectrometry (EDS) results show the presence of Bi2O3 phase in the grain-boundary region. The Seebeck coefficient (S) increased with increasing Bi content due to the decrease in the hole carrier concentration after Bi doping. As the amount of Bi was increased, the electrical resistivity (ρ) initially decreased but then increased with further addition of Bi. Addition of small amount of Bi led to large decrease in electrical resistivity due to the increased amount of Bi2O3 phase in the grain-boundary region. With further increase of Bi addition, the electrical resistivity increased due to the decrease in the hole carrier concentration. Optimum Bi doping not significantly affecting the hole carrier concentration is an effective approach for increasing the Seebeck coefficient and decreasing the electrical resistivity of Ca-349.

Magnetic properties and magnetocaloric effect in La0.7Sr0.3−xBixMnO3 manganites

Structural properties, magnetization and magnetocaloric effect measurements in the compounds based on lanthanum–strontium–bismuth manganites La0.7Sr0.3−xBixMnO3 (LSBiMO) with 0.05⩽x⩽0.30 have been performed. The valence states of elements entering into the composition of investigated LSBiMO samples were analyzed for x=0.15 and 0.3 using the HR XPS spectra of Bi 4f, La 3d, Mn 3s and Sr 3d. According to X-ray powder diffraction data the crystalline structure of the samples is perovskite-like with a small rhombohedral distortion. The a and c lattice parameters and unit cell volume V are established to increase with increasing Bi content. All the manganites show ferromagnetic-like ordering with second order phase transition to paramagnetic state. The Curie temperature and magnetization decrease at substitution of Sr2+ for Bi3+ ions. The magnetic entropy changes were calculated using the field dependence of isothermal magnetization in the terms of the thermodynamic Maxwell relation. The maximum magnetic entropy change value was shown to be 0.94Jkg−1K−1 for x=0.05 for a field change of 1T.

Structural, Magnetic, and Magnetocaloric Properties of La1−x Bi x MnO3 (x = 0.01, 0.03, 0.06, 0.1, 0.2) Compounds

Bi-doped lanthanum manganites with chemical composition of La1−x Bi x MnO3 (x = 0.01, 0.03, 0.06, 0.1, and 0.2) were prepared by a standard solid-state process. Magnetic and magnetocaloric properties of the samples were investigated in detail. X-ray diffraction measurement showed that the sample crystallized in the single phase of orthorhombic structure. It was found that the magnetization, Curie temperature, and the maximum value of magnetic entropy change decrease with increasing Bi content. The decrease in magnetic entropy change was attributed to the decrease in saturation magnetization and a change of the nature of the phase transition from first order to second order with increasing Bi content.

Bi flux-dependent MBE growth of GaSbBi alloys

The incorporation of Bi in GaSb1−xBix alloys grown by molecular beam epitaxy is investigated as a function of Bi flux at fixed growth temperature (275°C) and growth rate (1μmh−1). The Bi content is found to vary proportionally with Bi flux with Bi contents, as measured by Rutherford backscattering, in the range 0<x≤4.5%. The GaSbBi samples grown at the lowest Bi fluxes have smooth surfaces free of metallic droplets. The higher Bi flux samples have surface Bi droplets. The room temperature band gap of the GaSbBi epitaxial layers determined from optical absorption decreases linearly with increasing Bi content with a reduction of ~32meV/%Bi.

Dielectric properties of Bi-Doped BaTiO3-based ceramics synthesized by liquid-state method

A liquid-state method was used in this work to produce Bi-BaTiO3 materials. The dielectric properties of the samples were measured by a LCR meter. With increasing Bi content, the Multilayer ceramic capacitors display a stronger performance in its dielectric behavior. The best dielectric properties was obtained in the composition x = 0.02 with ɛ = 17561. The dielectric strength of the ceramics was measured by a withstanding voltage tester. The best dielectric strength was achieved in the comp+osition x = 0.02 with E = 4.545 kV mm−1.

Photoluminescent and photocatalytic properties of bismuth doped strontium aluminates blended with titanium dioxide

Bismuth co-doped long persistent phosphor (LPP) powders were obtained by a combustion synthesis technique followed by a post-annealing under carbon atmosphere. Bismuth content was varied from 1.0 to 15.0mol%. X-ray diffraction analysis revealed that the powders show mainly a mixture of three phases: the SrAl2O4, the SrAl14O25 and the Sr2Al6O11 crystalline phases. Photocatalyst composites were obtained by wet mixing of TiO2 anatase and LPP powders followed by annealing in air at 450°C. Photoluminescence measured spectra under 380nm excitation show a tunable emission from green (510nm) to greenish-blue (463nm) in which peak wavelength localization is related to the Bi content. Photoluminescence intensity decreases as Bi content increases. Degradation of methylene blue solutions, irradiated by UV light (254nm), was monitored by the decrease of its 650nm absorption peak in regular periods. The best photocatalytic activity is observed when in the composite blend a 2.0mol% of Bi content was used, and complete methylene degradation is reached after 210min. These photocatalyst composite powders are potential candidates to clean-up wastewater applications, and might be potential candidates for photocatalytic hydrogen generation in aqueous solutions.

Photoreflectance and photoluminescence study of localization effects in GaAsBi alloys

Photoreflectance (PR) and photoluminescence (PL) spectra of GaAs1−xBix alloys grown by metalorganic vapor phase epitaxy, for x up to 4.8%, were measured at temperatures ranging from 12 to 300K. The PR signal shifts due to the temperature change decreases with increasing Bi content of GaAsBi alloys. For temperature below 100K, a dominant peak in PL spectra of GaAsBi was observed. This peak is attributed to carrier localization resulting from Bi-related localized states in GaAsBi. A decrease in PR signal has been also found when the temperature was lowered. This behavior is attributed to a weakening of modulation efficiency, which is induced by carrier localization that has been evidenced in low temperature PL. The localized state emission partly contributes to the decrease in the band gap energy shift. In addition, at high temperatures the small PR signal shift is due to the reduction in the temperature dependence of the band gap energy. The analysis of the band gap energy evolution with temperature using the Bose–Einstein statistical expression shows that the average phonon energy is much larger than that expected from the linear interpolation between GaAs and GaBi. This fact is related to the interaction between electrons and phonons localized at Bi atoms playing an important role in the reduction of the temperature dependence of the band gap energy of GaAsBi alloys.

Photoluminescence properties of Y0.5−xGd0.35Eu0.15BixNbO4 (0 ≤ x ≤ 0.30) and Y0.35Gd0.35Eu0.15Bi0.15Nb1−yPyO4 (0 ≤ y ≤ 0.20) phosphors

The Y0.5−xGd0.35Eu0.15BixNbO4 (0≤x≤0.30) and Y0.35Gd0.35Eu0.15Bi0.15Nb1−yPyO4 (0≤y≤0.20) phosphors have been synthesized by the conventional solid-state reaction. For these Y0.5−xGd0.35Eu0.15BixNbO4 (0≤x≤0.30) samples, the emission increases and then decreases with increasing Bi content, and the maximum emission is achieved when x is 0.18. As for the Y0.35Gd0.35Eu0.15Bi0.15Nb1−yPyO4 (0≤y≤0.20) samples, the emission and excitation intensities are both varied with the P doping content. The strongest intensity is obtained in the case of y=0.15. These results indicate that the Bi dopant acts as one sensitizer and enhances the photoluminescence intensity. The introduction of PO43− also plays an important role in the photoluminescence properties of the investigated samples. The relevant mechanism has been also presented.

Bandgap and optical absorption edge of GaAs1−xBix alloys with 0 &amp;lt; x &amp;lt; 17.8%

The compositional dependence of the fundamental bandgap of pseudomorphic GaAs1−xBix layers on GaAs substrates is studied at room temperature by optical transmission and photoluminescence spectroscopies. All GaAs1−xBix films (0 ≤ x ≤ 17.8%) show direct optical bandgaps, which decrease with increasing Bi content, closely following density functional theory predictions. The smallest measured bandgap is 0.52 eV (∼2.4 μm) at 17.8% Bi. Extrapolating a fit to the data, the GaAs1−xBix bandgap is predicted to reach 0 eV at 35% Bi. Below the GaAs1−xBix bandgap, exponential absorption band tails are observed with Urbach energies 3–6 times larger than that of bulk GaAs. The Urbach parameter increases with Bi content up to 5.5% Bi, and remains constant at higher concentrations. The lattice constant and Bi content of GaAs1−xBix layers (0 &amp;lt; x ≤ 19.4%) are studied using high resolution x-ray diffraction and Rutherford backscattering spectroscopy. The relaxed lattice constant of hypothetical zincblende GaBi is estimated to be 6.33 ± 0.05 Å, from extrapolation of the Rutherford backscattering spectrometry and x-ray diffraction data.

Developments of high strength Bi-containing Sn0.7Cu lead-free solder alloys prepared by directional solidification

Bi-containing Sn0.7Cu (SC) eutectic solder alloys were prepared and subjected to directional solidification, through which new types of fiber reinforced eutectic composites were generated. The influences of Bi addition on the microstructures and tensile properties of directionally solidified (DS) Bi-containing eutectic SC lead-free solder alloys have been investigated by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and a tensile testing machine. The experimental results showed that addition of Bi could effectively reduce both the melting temperature and undercooling of SC solder alloy. The microstructures of DS SC–xBi solder alloys were composed of Sn-rich phase (β) and Cu6Sn5 fiber. No other intermetallic compounds (IMCs) with Bi content were observed in the solder matrix for SC solder alloys with various Bi contents. Both fiber spacing and diameter all decreased gradually with increasing growth rate and/or Bi content. Besides, the regularity of Cu6Sn5 fibers alignment also decreased with increasing growth rate, too. The tensile strengths of the SC–xBi eutectic solder alloys varied parabolically with growth rate (R). When R was 60μm/s, maximum tensile strengths of 43.8, 55.2 and 56.37MPa were reached for SC, SC0.7Bi and SC1.3Bi solder alloys. A comparison of tensile strength of SC, SC0.7Bi and SC1.3Bi with the same R indicated that the tensile strength increased with increasing Bi content, which was attributed to the presence of Bi and its role in refining microstructure and solid solution strengthening.

Effects of Bi2O3 Addition in Micro- and Nanoscale on the Structural and Electrical Properties of Zn1-xBixO varistors

Two similar sets of Zn1-xBixO ceramic varistors with various x values (0.00 ≤x≤ 0.20) have been prepared by using Bi2O3 additions with two different sizes. In the first set, Bi2O3 nanoparticles (≈200 nm) were used, while Bi2O3 microparticles (≈5 μm) were used in the second set. It was found that addition of Bi up to 5 % for both sets did not affect the wurtzite-type hexagonal structure of ZnO, but with increasing Bi above 5 %, some unknown lines were clearly observed in XRD spectra. The grain sizes are increased in both sets with increasing Bi content up to 2.5 %, followed by a decrease with further increase of Bi up to 20 %, and their values for microparticle additions were larger than that of the sets containing nanoparticle additions. Two nonlinear regions were formed in the I–V curves of ZnO due to Bi2O3 nanoparticle additions above 5 %. However, this behavior was completely absent in the samples containing Bi2O3 microparticles. Moreover, the breakdown field and nonlinear coefficient decreased with Bi2O3 addition up to 5 % for both sets, followed by an increase with further increase of Bi up to 20 %, and their values were higher for nanoparticle additions than that of microparticles. A reverse behavior was recorded for the electrical conductivity. The results have been discussed in terms of Bi2O3 nanosize grains which may be localized at the grain boundaries of ZnO ceramics.

High Bi content GaSbBi alloys

The epitaxial growth, structural, and optical properties of GaSb1–xBix alloys have been investigated. The Bi incorporation into GaSb is varied in the range 0 &amp;lt; x ≤ 9.6% by varying the growth rate (0.31–1.33 μm h−1) at two growth temperatures (250 and 275 °C). The Bi content is inversely proportional to the growth rate, but with higher Bi contents achieved at 250 than at 275 °C. A maximum Bi content of x = 9.6% is achieved with the Bi greater than 99% substitutional. Extrapolating the linear variation of lattice parameter with Bi content in the GaSbBi films enabled a zinc blende GaBi lattice parameter to be estimated of 6.272 Å. The band gap at 300 K of the GaSbBi epitaxial layers decreases linearly with increasing Bi content down to 410 ± 40 meV (3 μm) for x = 9.6%, corresponding to a reduction of ∼35 meV/%Bi. Photoluminescence indicates a band gap of 490 ± 5 meV at 15 K for x = 9.6%.

Transport properties of Bi-doped FeSe superconductor up to 700 K

Polycrystalline samples of Fe1-xBixSe with x = 0.00, 0.02, 0.05, and 0.08 are prepared by conventional solid state reaction. The resistivity and thermopower are measured up to 700 K. The onset superconducting transition temperature decreases slightly with increasing Bi content. Transport behavior of electrical resistivity in the normal state is quite complex. A linear temperature dependence is found between 20 and 100 K. Above 150 K, the electrical resistivity behavior resembles misfit-layered cobalt oxides Ca3Co4O9+δ; a Fermi-liquid behavior of T2 dependence is observed between 150 and 210 K with the Fermi-liquid transport coefficient A having the size between 4.3 × 10−6 and 10 × 10−6 mΩ-cm/K2, followed by an incoherent metal and a high-temperature nonmetal-like behavior. Thermopower behavior is nonconventional. Sign crossover of thermopower occurs both below and above room temperature. According to the dynamical mean field calculations, the negative dip feature of thermopower between 110 and 130 K seems to be associated with excitations of a pseudogap ground state.

High Curie temperature BiInO3-PbTiO3 films.

High Curie temperaturepiezoelectricthin films of xBiInO3-(1-x)PbTiO3 (x = 0.10, 0.15, 0.20, and 0.25) were prepared by pulsed laser deposition. It was found that the tetragonality of films decreased with increasing BI content. The dielectric constant and transverse piezoelectric coefficient (e31,f ) exhibit the highest values of 665 and -13.6 C/m2 at x = 0.20. Rayleigh analyses were performed to identify the extrinsic contributions to dielectric nonlinearity with different x. The composition with x = 0.20 also exhibits the largest extrinsic contributions to dielectric nonlinearity. The Curie temperature (TC ) is increased with increasing x content from 558 to 633 °C; TC at x = 0.20 is about 584 °C.

Bismuth-induced effects on optical, lattice vibrational, and structural properties of bulk GaAsBi alloys

Bulk GaAs1 - xBix/GaAs alloys with various bismuth compositions are studied using power- and temperature-dependent photoluminescence (PL), Raman scattering, and atomic force microscopy (AFM). PL measurements exhibit that the bandgap of the alloy decreases with increasing bismuth composition. Moreover, PL peak energy and PL characteristic are found to be excitation intensity dependent. The PL signal is detectable below 150 K at low excitation intensities, but quenches at higher temperatures. As excitation intensity is increased, PL can be observable at room temperature and PL peak energy blueshifts. The quenching temperature of the PL signal tends to shift to higher temperatures with increasing bismuth composition, giving rise to an increase in Bi-related localization energy of disorders. The composition dependence of the PL is also found to be power dependent, changing from about 63 to 87 meV/Bi% as excitation intensity is increased. In addition, S-shaped temperature dependence at low excitation intensities is observed, a well-known signature of localized levels above valence band. Applying Varshni’s law to the temperature dependence of the PL peak energy, the concentration dependence of Debye temperature (β) and thermal expansion coefficient (α) are determined. AFM observations show that bismuth islands are randomly distributed on the surface and the diameter of the islands tends to increase with increasing bismuth composition. Raman scattering spectra show that incorporation of Bi into GaAs causes a new feature at around 185 cm-1 with slightly increasing Raman intensity as the Bi concentration increases. A broad feature located between 210 and 250 cm-1 is also observed and its intensity increases with increasing Bi content. Furthermore, the forbidden transverse optical (TO) mode becomes more pronounced for the samples with higher bismuth composition, which can be attributed to the effect of Bi-induced disorders on crystal symmetry.PACS78.55Cr 78.55-m 78.20-e 78.30-j