Increasing Bi Content Research Articles

Magnetic and Dielectric Properties of La and Ni Co-substituted BiFeO3 Nanoceramics

The increasing plead for the realization of ultra-fast, miniaturize, compact and ultra-low power consumption in electronic as well as spintronic devices has propelled the quest for novel multiferroic materials which enable voltage control of magnetism in an energy efficient way. The present work reports the phase stability, magnetic and dielectric properties of polycrystalline Bi1-xLaxFe1-yNiyO3 (0≤x≥0.2 and 0≤y≥0.2) multiferroic ceramics synthesized through a simplistic sol-gel approach. The maneuver substitutions of La at Bi site in the BiFeO3 multiferroic eliminate the usual impurity phases. Rietveld refined XRD patterns reveals the structural evolution of orthorhombic (Pbnm) phase with the increasing Bi content at La site and further Ni substitutions at Fe sites induces the lattice distortion. A substantial enhancement in multi-ferroic behaviour has been observed for Ni and La co-substituted samples, due to the size confinement effect of nano-crystallites, the exchange interaction between Fe3+ and Ni2+ ions and corresponding change in Fe-O-Fe bond angles led by the co-substitution. The dielectric constant has observed to be increased by two-fold in the low frequency region with the La and Ni co-substitutions at A (Bi) and B (Fe) -sites respectively. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves show spin glass like behavior with an embedded ferromagnetic component. The results indicate that the co-substitutions of La and Ni at the respective sites of Bi1-xLaxFe1-yNiyO3 (0≤x≥0.2 and 0≤y≥0.2), can significantly improve the ferromagnetic and dielectric properties of BiFeO3 nanoceramics.

Characterization of tellurium and silicon as n-type dopants for GaAsBi

Films of n-GaAs1-xBix films were grown via molecular beam epitaxy using both Si and Te as dopant sources. Electron mobility was characterized by Hall effect measurements as a function of carrier concentration and Bi content for films with bismuth fractions of x = 0.02 and x = 0.06. While GaAsBi:Te shows lower majority carrier mobility than GaAsBi:Si at low Bi concentrations, the two become comparable as Bi content increases. Furthermore, it was observed that in the presence of bi-metallic Bi-Ga droplets on the film surface, films doped with Si display p-type behavior, likely due to Si preferentially occupying group-V sites. The use of Te as a dopant always resulted in n-type epilayers, making it a more reliable dopant choice for high Bi content films. Finally, ex situ annealing was studied as a method to improve majority carrier mobility in GaAs0.98Bi0.02:Te films, with a 10 min anneal at 350 °C resulting in a 30% improvement in electron mobility. Improvement of film quality was confirmed through spectroscopic ellipsometry examination of film optical properties. Annealing at higher temperatures resulted in electrical, optical, and structural degradation of the GaAsBi films.

Structural, photocatalytic and electroconductive properties of bismuth-substituted CaMoO4

The Ca1−3xBi2xФxMoO4 system (0.025 ​≤ ​x ​≤ ​0.30, where Ф represents cation vacancies) was synthesized and studied. The 0.025 ​= ​x ​≤ ​0.15 compositions show a tetragonal defect scheelite structure. Powder X-ray and neutron diffraction patterns for compositions with 0.15 ​< ​x ​≤ ​0.225 exhibit a tetragonal supercell with asup ​≈ ​√5a, csup ​≈ ​c where a and c are the tetragonal scheelite cell parameters. Transmission electron microscopy shows that Ca0.4Bi0.4MoO4, crystals consist of three crystallographic domains: (1) defect scheelite; (2) tetragonal superlattice and (3) incommensurately modulated. Photocatalytic properties were studied using Rhodamine B water solutions under UV light. Catalytic activity increases with increasing Bi content. The conductivity of 0.15 ​< ​x ​≤ ​0.225 compositions is 10−7 to 10−8 ​S ​cm−1 in the range 500–650 ​°C, while compositions in the range 0.025 ​= ​x ​≤ ​0.15 show conductivity values from 10−3 to 10−8 ​S ​cm−1 from 500 to 800 ​°C.

Antiferromagnetic-ferromagnetic transition in Bi-doped LaFeO3 nanocrystalline ceramics

A series of nanocrystalline La1-xBixFeO3 (0.0≤x ≤ 0.5) ceramic powders were successfully prepared by the sol-gel method. X-ray diffraction and transmission electron microscopy were used to investigate the crystal structure evolution and hyperfine interactions of the samples. The average diameter of the powders was revealed to be approximately 80 nm. All the samples were crystallized into an orthorhombic crystal structure (space group Pnma) with no second phase. The magnetization of the Bi-doped samples obviously improved with increasing Bi content. A remarkable antiferromagnetic/ferromagnetic transition was detected at x ≥ 0.2, and a high coercive field of 23.05 kÖe was obtained with x = 0.5. The high correlation between the magnetization parameters and bonding characteristics indicated that significant stretching of the Fe3+-Od2- bonds and a decrease in Fe3+-Od2--Fe3+ linkage angles were the main origins of the strong ferromagnetism in the Bi-doped systems.

Magnetic phase transformation in La0.7-xBixSr0.3MnO3 (0.25 ≤ x ≤ 0.40)

We have observed cross over from Ferromagnetism (FM) to Anti-ferromagnetism (AFM) accompanied by spin lattice coupling in La0.7-xBixSr0.3MnO3 as La is partially replaced by Bi (0.25 ≤ x ≤ 0.40) through structural, magnetization and electrical resistivity studies. Ferromagnetic metallic (FMM) phase observed in x = 0.25 sample transforms to antiferromagnetic insulating (AFI) phase with increasing Bi content (x = 0.40). The step like behavior in M(H), i.e. the metamagnetic transition, describes the field induced antiferromagnetic to ferromagnetic transition in x = 0.30 and 0.35 samples. The irreversibility in the field dependent resistivity and magnetization suggests the competitive phase coexistence, between AFM and FM phases, in x = 0.30 and 0.35 samples. The anomaly in the structural parameters across the electrical and magnetic transition observed from the analysis of synchrotron X-ray diffraction data, at low temperatures, establishes a strong interplay between spin lattice coupling in all four samples studied here. The present study thus clearly brings out cross over from FMM to AFI state as Bi concentration increases in La0.7-xBixSr0.3MnO3.

Effect of Bi contents on key physical properties of NiO NPs synthesized by flash combustion process and their cytotoxicity studies for biomedical applications

Nickel oxide has tremendous applications in the field of biomedicine. In this study, NiO nanoparticles were synthesized with different Bi contents (NiO@Bi; 0.0–7.5 wt%), and multifunctional usages were investigated. Structural confirmation was conducted through XRD and Raman studies, which revealed a monophasic cubic system. With increasing Bi content, broadening of the XRD and Raman peaks were observed, indicating a reduction in particle size. The crystallite size was found to be in the range of 10–26 nm. The decrease in particle size was confirmed through dynamic light scattering measurement. The homogeneous distribution of all elements and the presence of Bi were detected by an EDX/SEM e-mapping study. Field emission electron microscopy confirmed the formation of spherical shape nanoparticles. The grain size was reduced from 30 nm to 10 nm with Bi content, in accordance with XRD and Raman results. The Kubelka-Munk method was employed to determine the effect of Bi content on the optical band gap of NiO. The energy gap was reduced with Bi content in the range of 3.32–3.50 eV. Antimicrobial and in vitro cytotoxic characteristics of the prepared NPs were also studied. The results revealed that all NiO@Bi NPs had negligible antimicrobial activity and no cytotoxic effects on both normal and activated splenic cells. The invivo acute cytotoxicity study indicated no cytotoxic effects on liver and kidney functions. The prepared NiO@Bi NPs were implanted in living organisms without hepatic/renal toxicity, demonstrating excellent biocompatibility, cell viability, and superior quality of nanocrystals, suggesting that the prepared NPs are ideal candidates for antibacterial and biomedical applications.

Solid-State Synthesis and Thermoelectric Properties of Tetrahedrites Cu12Sb4-yBiyS13

Tetrahedrite has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. The synthesis of tetrahedrite compounds by conventional melting methods requires a long-time reaction and annealing. However, a homogeneous and solid-state synthesis can be conducted in a short time using mechanical alloying (MA) because the volatilization of the constituent elements is inhibited and a subsequent heat treatment is not necessary. In this study, Bi-doped tetrahedrites Cu12Sb4-yBiyS13 (y = 0-0.4) were prepared by MA and hot pressing. X-ray diffraction analyses revealed that all specimens consisted of single-phase tetrahedrite. However, with increasing Bi content, skinnerite Cu3SbS3 was detected. The electrical conductivity increased and the Seebeck coefficient deceased with increasing Bi content as result of the substitution of Bi at Sb sites. In addition, the thermal conductivity increased as the Bi content increased because of the increase in electronic thermal conductivity. A high dimensionless figure of merit of 0.88 was obtained at 723 K for Cu12Sb3.9Bi0.1S13.

Dielectric analysis and electrical conduction mechanism of La1-x Bi x FeO3 ceramics.

Bulk-phase polycrystalline La1−xBixFeO3 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were prepared by citric sol–gel and sintering methods. The structural, morphological, and electrical properties of the resulting sol–gel solutions were investigated using various techniques. In an X-ray diffraction analysis, all samples crystallized in the orthorhombic structure with the Pbnm space group and showed an increase in lattice constant with increasing Bi content which was also confirmed by vibrational analysis. The sample surfaces and average grain sizes were examined by scanning electron microscopy. The grain distribution was non-uniform and the grain size increased with the increasing Bi content. The complex electrical conductivities and dielectric analyses of these materials were investigated as functions of frequency by impedance spectroscopy at various temperatures (75–200 °C). The frequency-dependent dielectric constant at each temperature increased with increasing Bi content. A Jonscher's power law analysis revealed that the AC and DC conductivities arose by completely different mechanisms. The temperature dependence and dielectric relaxation of the DC conductivity satisfied the Arrhenius law and decreased with increasing Bi content. The activation energy ranged from 0.20 to 0.45 eV and was similar in the conduction and relaxation mechanisms, indicating that both transport mechanisms were based on hopping phenomena. We believe that lowering the activation energy will help with the optimization of constituents as promising candidates in novel materials for future electrocatalysts.

Oxygen Activation through β-Bi2O3 and Ultrafine CeO2 Interactions to Promote Catalytic Soot Combustion

Herein, we report the high performance of Bi2O3 interacted with ultrafine CeO2 nanoparticles (NPs) for soot oxidation. With the increased Bi content, Bi2O3 can be tuned from the amorphous phase to ...

Synthesis and optical properties of colloidal Cs2AgSb1-xBixCl6 double perovskite nanocrystals.

Lead halide perovskites are extraordinary optoelectronic materials, but there are issues related to their toxicity and instability. To overcome these issues, various lead-free perovskites are being explored. Metal halide double perovskites, for example, Cs2AgSbCl6, in which two Pb2+ in CsPbCl3 (or Cs2Pb2Cl6) are replaced with one Ag+ and one Sb3+, provide both charge balanced and stable 3D perovskite structures. Synthesis of such double perovskites with different compositions, sizes, and solution processabilities still remains a challenge. The present communication describes synthesis and characterization of colloidal Cs2AgSb1-xBixCl6 alloy nanocrystals with 0 ≤ x ≤ 1. These nanocrystals exhibit an elpasolite structure where the lattice parameters vary systematically with the composition "x." The nanocrystals are cubic in shape with an edge-length of ∼10 nm. UV-visible absorption spectra also change systematically with composition. The lowest energy absorption peak ∼3.4 eV becomes sharper along with a red-shift with increasing Bi content. The alloying can influence the optical absorption by both modifying the intrinsic electronic band structure and changing the concentration of antisite disorders. For intermediate compositions (x = 0.22, 0.36, and 0.70), photoluminescence with a peak at 2.74 eV is observed.

XPS on Nd0.6-xBixSr0.4MnO3 nano powders

The structural and electronic properties on Nd0.6-xBixSr0.4MnO3 nano powders with x = 0, 0.05 and 0.1 are reported. The compounds were prepared using sol-gel combustion method. X-ray diffraction studies confirm that all samples crystallize in orthorhombic structure having Pnma space group. The powders consist of spherical particles that tend to agglomerate, with average grain sizes of about 40–50 nm. XPS measurements reveal a shift toward lower binding energies of Mn 3s, Mn 2p, Nd 3d, and O 1s core levels with increasing Bi content, which can be explained by the larger ‘c’ lattice parameter and therefore larger atomic distances. The analysis of the core level XPS spectra proves the existence of both Mn4+ and Mn3+ ions in all samples, as well as the localization of Bi3+ ions in the perovskite lattice. The XPS valence-band is dominated by extensively hybridized Nd 4f-O 2p states, with contributions from Mn 3d-O 2p bonding and Mn 3d states.

Enhanced multiferroic properties of Bi0.85Nd0.15FeO3 ceramics with excess Bi2O3

Multiferroic Bi(1+x)×0.85Nd0.15FeO3 (BNF) ceramics with various Bi contents are prepared by conventional solid state reaction, and the effects of excess Bi on the structure, morphology, dielectric, ferroelectric, and magnetic properties are investigated. XRD patterns show the coexistence of rhombohedral and orthorhombic phase in all BNF ceramics due to the doping of Nd3+ ions. Bi2Fe4O9 and Bi2O3 impurity can be observed in x = 0 and x = 5%, 7.5% ceramics, respectively. Surface morphologies are closely related to the Bi content and x = 2.5% sample exhibits the largest average grain size of ∼6.72 μm. The leakage current density has been decreased by 3–4 orders of magnitudes through excess Bi. The x = 2.5% sample shows good ferroelectric property with typical hysteresis loop and a large remnant polarization of about 42 μC/cm2 at 150 kV/cm. The P-E hysteresis deteriorates in x = 5% and x = 7.5% ceramics. The PbZrO3-like superstructure related to 1/4(hh0)p diffraction spots in SAED pattern can be found in all BNF ceramics and the number of grain with superstructure observed in each sample decreases as the Bi content increases. As Bi content increases, the remnant magnetization decreases at first, and then increases. Conversion-electron Mossbauer study have ruled out the impacts of Fe2+, Fe4+, or γ-Fe2O3 on the magnetic properties, suggesting that the weak ferromagnetism comes from the destroy of spin cycloid through substitution of Bi3+ ions with Nd3+ ions. Excessive Bi3+ ions have weakened the effect of Nd3+ ions on suppression of spin cycloid and resulted in the degradation of magnetic properties. The slight improvement of magnetic properties in x = 7.5% sample is considered to attribute to Fe vacancies induced by excessive Bi.

The factors determining the band gap energy of the As-rich GaBixAs1−x

The band gap energy in the As-rich GaBixAs1−x alloy is studied and a modified model is set up. It is found that the impurity–impurity interaction determined by the Bi pairs and Bi clusters should be taken into consideration. It is also found that when the Bi content increases, the band gap energy of GaBixAs1−x goes through from the impurity-like region to the band-like region in the As-rich range. In the impurity-like region, the Г VBM of GaBixAs1−x plays a more important role than the Г CBM in the band gap reduction. Under this condition, the impurity–host interaction in the valence band should be the most important factor to determine the band gap energy. On increasing Bi content, the Г VBM of GaBixAs1−x gradually shows a weaker composition dependence than Г CBM due to the influence of the localized Bi levels. In this case, the most important factor determining the band gap energy is the impurity–host interaction in the conduction band.

Structural analysis and dielectric properties of La1-xBixFeO3 perovskite materials at room temperature

Perovskites La1-xBixFeO3 (x = 0.1, 0.3, and 0.5) were prepared by sol-gel method. Structural characterization was performed by X-Ray diffraction (XRD) and X-Ray Fluorescence (XRF). Based on refinement results of XRD analysis, the samples shown the single phase orthorhombic structure with Pnma space group. The dielectric constant and loss factor of the bulk samples were investigated by using LCR-Meter in the frequency range of 100 Hz-1 MHz at room temperature. Increasing Bi content caused decreasing dielectric constant. It may be correlated with decreasing the density of sample with Bi-doped.

Influence of Bi on the thermoelectric properties of SrTiO3-δ

The thermoelectric properties of Sr1-xBixTiO3-δ (0 ≤ x ≤ 0.07) have been investigated. Dense ceramics of Sr1-xBixTiO3-δ and Sr0.95TiO3-δ have been prepared by solid-state reaction and conventional sintering in air followed by annealing in a reducing atmosphere. XRD and SEM analyses show that the rutile TiO2 in Sr0.95TiO3 formed after sintering becomes Magnéli phase of TinO2n-1 after annealing. Moreover, Bi resolves from Sr1-xBixTiO3 after annealing, resulting in the formation of Sr1-xBixTiO3-δ/Bi/TinO2n-1 composites. With increasing Bi content in Sr1-xBixTiO3-δ, the electrical conductivity increases while the absolute values of the Seebeck coefficient decrease as a result of increasing carrier concentration. The thermal conductivity of SrTiO3-δ is reduced by doping Bi up to x = 0.07. Highest ZT ∼0.13 is obtained in Sr0.93Bi0.07TiO3-δ at 1000 K.

Raman spectroscopic determination of hole concentration in undoped GaAsBi

Raman spectra of undoped GaAs1−xBix (0 < x < 0.037) grown on GaAs by molecular beam epitaxy were investigated. With an increase of Bi component, we find that the longitudinal optical phonon-hole-plasmon-coupled (LOPC) mode first appears in the vicinity of the unscreened longitudinal optical (ULO) phonon frequency, and then shifts towards the transverse optical (TO) phonon frequency. A new vibrational mode (∼287 cm−1) between the TO and the ULO phonons was verified by use of low temperature polarized Raman measurement and the corresponding scattering intensities are found to be linearly proportional to the composition of Bi in GaAsBi. The hole concentrations determined by using the LOPC/ULO Raman intensities ratio increase from ∼6.5 × 1016 to ∼2.8 × 1017 cm−3 with increased Bi content and the measured results are in agreement with Hall measurements. Furthermore, the influence of excitation laser power on the estimation of the hole densities is discussed with the help of power dependent Raman spectroscopy.

Terahertz excitation spectra of GaAsBi alloys

Terahertz excitation spectroscopy was used for the determination of energy separation between the main (Γ) and subsidiary (L and X) conduction band valleys of GaAs1−xBix. The samples used in this study were 1 µm–1.5 µm thick bismide layers grown by Molecular Beam Epitaxy on GaAs substrates. They contained up to 8% of bismuth as determined by high resolution x-ray diffraction (HR-XRD) and reciprocal space mapping (RSM), taking into account the layer relaxation. It was found that both subsidiary conduction band valleys at L and X points of the Brillouin zone move away from the conduction band minimum at rates of 18 meV/%Bi and 25 meV/%Bi, respectively, with increasing Bi content in the alloy.

Study of the Microstructure, Mechanical, and Magnetic Properties of LaFe11.6Si1.4Hy/Bi Magnetocaloric Composites.

We have successfully synthesized LaFe11.6Si1.4Hy/Bi composites by cold pressing together with vacuum annealing technology, and systematically investigated the microstructure, magnetism, mechanical performance, and magnetocaloric properties. LaFe11.6Si1.4Hy particles are well surrounded by metallic Bi, without the formation of new phase. The maximum values of the volumetric magnetic entropy change -ΔSM are as high as 51, 49, and 35 mJ/cm3K around 263 K, for the composites with 5, 10 and 15 wt % Bi contents, respectively. The maximum value of the compressive strength for LaFe11.6Si1.4Hy/Bi composites increased continuously from 155 to 358 MPa with increasing Bi content, from 0 to 15 wt %.

The localized effect of the Bi level on the valence band in the dilute bismuth GaBixAs1-x alloy

The research on the temperature dependence of the band gap energy of the dilute bismuth GaBixAs1-x alloy has been done. It is found that its temperature insensitiveness is due to the enhanced localized character of the valence band state and the small decrease of the temperature coefficient for the conduction band minimum (CBM). The enhanced localized character of the valence band state is the main factor. In order to describe the localized effect of the Bi levels on the valence band, the localized energy is introduced into the Varshni's equation. It is found that the effect of the localized Bi level on the valence band becomes strong with increasing Bi content. In addition, it is found that the pressure dependence of the band gap energy of GaBixAs1-x does not seem to be influenced by the localized Bi levels. It is due to two factors. One is that the pressure dependence of the band gap energy is mainly determined by the Г CBM of GaBixAs1-x. The Г CBM of GaBixAs1-x is not influenced by the localized Bi levels. The other is that the small variation of the pressure coefficient for the Г valence band maximum (VBM) state of GaBixAs1-x can be cancelled by the variation of the pressure coefficient for the Г CBM state of GaBixAs1-x.

Structural and optical properties of GaSbBi/GaSb quantum wells [Invited

GaSbBi/GaSb quantum wells (QWs) with Bi content up to 10.1% were grown using molecular beam epitaxy. High crystalline quality and clear interfaces were confirmed by high resolution transmission electron microscopy. The Bi distribution was investigated using energy dispersive X-ray spectroscopy. Room temperature photoluminescence (PL) reveals that the peak energy redshifts at a rate of 32 meV/Bi%, consistent with the theoretical predication using the 8-band kp model. From the temperature dependent PL, it was found that the temperature-insensitivity of the transition from the GaSbBi QW improved with increasing Bi content.