Polycrystalline Bi Research Articles

Thermoelectric properties of p-type polycrystalline Bi0.8Sb0.8In0.4Se3

Achieving both n-type and p-type performance in one thermoelectric material family is of great benefit for the thermoelectric device due to the comparable mechanical properties. Bi2Se3 shows strong n-type behavior due to the intrinsic Se vacancy. Herein, we reported a p-type poly-crystalline Bi0.8Sb0.8In0.4Se3 material, which has the same crystalline structure as Bi2Te3, with an intrinsic Seebeck coefficient of 500 μV K−1 at room temperature. It is found that Mn is a good p-type charge carrier provider in the as-fabricated Bi0.8Sb0.8In0.4Se3 thermoelectric material. An optimized power factor of ∼420 μW m−1 K−2 and a low thermal conductivity of 0.51 W m−1 K−1 result in a ZT of 0.48 at 350 °C in Mn0.03Bi0.77Sb0.8In0.4Se3. Our work provides an incisive insight into the manipulation of the intrinsic defects via high entropy strategy.

Improvement of flux pinning properties in Fe3O4 nanoparticle-doped Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconductors

The flux pinning properties of polycrystalline (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1−x(Fe3O4)x, with x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05 superconductors were investigated. The collective pinning theory was successfully used to describe the magnetization critical current density (Jc) of all samples. The value of Jc was enhanced by the proper doping contents of Fe3O4 nanoparticles. Possible origins for these achievements were attributed to the increases in both flux pinning force and activation energy. The appearance of the additional point-like pinning centers was confirmed via Dew–Hughes model fitting analysis.

Eco-friendly Bi(Ni2/5Ti2/5Fe1/5)O3 nanoceramics: Synthesis, dielectric and impedance studies

This investigation involves the synthesis and study of dielectric, structural and impedance properties of polycrystalline Bi(Ni2/5Ti2/5Fe1/5)O3 (symbolized as BNTF) nano-ceramic. The BNTF polycrystalline sample was fabricated through the use of a conventional solid-state reaction route. X-ray structural examination reveals that the parent compound (i.e., BiFeO3) crystallizes in the rhombohedral structure (space group-R3c) while that the BNTF compound crystallizes in orthorhombic symmetry. The substitution of NiTiO3 into BiFeO3 enhances various properties and reduces electrical leakage current. The average crystallite size is calculated to be 29 nm. The room temperature textures and surface morphologies of the specimen were verified by field-emission scanning electron microscope, and show uniform grains distribution on sample surfaces. Dielectric parameters (constant and tangent-loss) and impedance spectroscopy parameters of NiTiO3 modified BiFeO3 compound were investigated over a wide temperature range (25–500 °C) at different frequency (25 kHz-500 kHz), which offers several interesting features of BNTF material suitable for further device applications.

Fabrication of high Jc Bi2223 thick films through grain alignment technique using a permanent magnet

In order to realize practical superconducting joints between Bi2223 tapes towards persistent-current magnets, Bi2223 thick films with high critical current density (Jc) suitable for joint intermediate layers are needed. On the other hand, the methodology of c-axis grain alignment for improving the critical current properties in the polycrystalline materials with a relatively large thickness has not been established. Although the magnetic grain alignment technique is known to be effective for Bi2223 materials, there have not been any successful studies achieving high intergrain Jc of Bi2223 polycrystalline materials prepared thorough the magneto-scientific method thus far. In the present study, fabrication and evaluation of the physical properties of the c-axis-aligned thick films obtained through grain alignment technique using a permanent magnet were performed. Improvement of the intergrain Jc according to the magnetic grain alignment was confirmed in the thick film samples. Control of the microstructure demonstrated in the present study is one of the promising way for realization of the practical superconducting joints between the Bi2223 commercial tapes.

Rational Electronic and Structural Designs Advance BiCuSeO Thermoelectrics

AbstractIn this work, a record high thermoelectric figure‐of‐merit ZT of 1.6 ± 0.2 at 873 K in p‐type polycrystalline Bi0.94Pb0.06CuSe1.01O0.99 by a synergy of rational band manipulation and novel nanostructural design is reported. First‐principles density functional theory calculation results indicate that the density of state at the Fermi level that crosses the valence band can be significantly reduced and the measured optical bandgap can be enlarged from 0.70 to 0.74 eV by simply replacing 1% O with 1% Se, both indicating a potentially reduced carrier concentration and in turn, an improved carrier mobility and a boosted power factor up to 9.0 µW cm−1 K−2. Meanwhile, comprehensive characterizations reveal that under Se‐rich condition, Cu2Se secondary microphases and significant lattice distortions triggered by Pb‐doping and Se‐substitution can be simultaneously achieved, contributing to a reduced lattice thermal conductivity of 0.4 W m−1 K−1. Furthermore, a unique shear exfoliation technique enables an effective grain refinement with higher anisotropy of the polycrystalline pellet, leading to a further improved power factor up to 10.9 µW cm−1 K−2 and a further reduced lattice thermal conductivity of 0.30 W m−1 K−1, which gives rise to record high ZT.

Chemical Solution Deposition of La-Substituted BiFe0.5Sc0.5O3 Perovskite Thin Films on Different Substrates

In the present work, polycrystalline Bi0.67La0.33Fe0.5Sc0.5O3 thin films were synthesized using a simple and cost-effective chemical solution deposition process employing the spin coating technique. In order to check the feasibility of the fabrication of thin films on various types of substrates, the films were deposited on Pt-coated silicon, silicon, sapphire, corundum, fused silica and glass. Based on the results of thermogravimetric analysis of precursor and thermal stability study, it was determined that the optimal annealing temperature for the formation of perovskite structure is 600 °C. It was observed that the relative intensity of the pseudocubic peaks (001)p and (011)p in the XRD patterns is influenced by the nature of substrates, suggesting that the formed crystallites have some preferred orientation. Roughness of the films was determined to be dependent on the nature of the substrate.

Kinetic-Controlled Growth of Bi Nanostructures for Electrocatalytic CO2 Reduction

Bi-based catalysts have attracted great attention for efficient electrocatalytic carbon dioxide (CO2) reduction to formic acid (HCOOH). However, the effect of the growth kinetics of Bi nanostructures on morphology and their catalytic performance has not been studied. Here, we varied the Bi3+ precursor concentration in the electrolyte to control the electrochemical growth rate of Bi nanostructures. It was found that the growth rate determines not only the geometric structure but also the microstructure of Bi nanostructures. The slow growth with a low precursor concentration (1 mM) produced Bi nano-sheet (NS) with high crystallinity in (012) preferred orientation. But, the polycrystalline Bi nano-branch (NB) with a larger surface area was formed by a faster growth condition (precursor concentration = 30 mM). As a result, Bi NB achieved a higher FEHCOOH of 97.1% than Bi NS (FEHCOOH = 81.5%) at −1.0 VRHE. This work reveals that the growth condition of the Bi nanostructures plays a significant role in designing the catalysts for the efficient CO2 reduction reaction.

Half Replacement of Bismuth by Neodymium in Half-Hole Doped Bismuth-Based Manganites Bi0.25Nd0.25X0.5MnO3 (X = Sr, Ca): a Neutron Diffraction Study

The effect of half substitution of diamagnetic Bi3+ with the rare earth magnetic Nd3+ ion on the magnetic and structural properties of the polycrystalline Bi0.25Nd0.25Sr0.5MnO3 and Bi0.25Nd0.25Ca0.50MnO3 was studied by X-ray and neutron diffraction complemented by magnetic measurement. We correlate the structural response of Bi0.25Nd0.25X0. 5MnO3 (X = Sr, Ca) for charging and spin ordering with a reduced amount of Bi3+, which in addition to its special contribution to itinerant eg electrons leads to a change in the average size of the A-site cations, 〈rA〉, and the mismatch between the A-site cations (size variance, σ 2). For both compounds, the corresponding charge ordering scheme and ground magnetic state of CE-type antiferromagnetic arrangement at 10 K were specified. An analysis of the data confirms that in Bi–Sr manganite a lone pair of 6s2 Bi3+ orbitals is dominant.

Effect of the crystal alignment and grain size on the thermoelectric properties of Bi0.4Sb1.6Te3 sintered materials

Sintered polycrystalline Bi0.4Sb1.6Te3 thermoelectric materials with various degrees of crystal alignment and grain sizes were prepared by pulse-current sintering under cyclic uniaxial pressure at sintering temperatures of 350–425 °C for holding times of 0–60 min to clarify the relationship between the microstructure and the thermoelectric properties. The degree of crystal alignment was enhanced with an increase of both the sintering temperature and holding time, and grain growth was also confirmed in the high temperature or long-time sintering process. The thermoelectric properties were measured perpendicular to the pressing direction, which corresponds to the crystal alignment direction. The electrical resistivity decreased and the thermal conductivity slightly increased with increasing sintering temperature and holding time. As a result, the figures of merit of the crystal-aligned samples sintered at high temperatures or for long holding times tended to reach 0.9–1 with large power factors because of the small electrical resistivity. The relationships between the quantified microstructure parameters and thermoelectric properties are discussed. The electrical resistivity decreased with increasing degree of crystal alignment and it saturated at a certain degree of crystal alignment, indicating that perfect crystal alignment is not necessary to obtain the lower limit of the electrical resistivity. Conversely, no significant change of the lattice thermal conductivity was observed in the grain size range 0.6–9.7 μm. This means that the lattice thermal conductivity of crystal aligned Bi0.4Sb1.6Te3 is almost independent of the degree of crystal alignment and grain size in the measured range.

Angular Distributions during Magnetron Sputtering of Polycrystalline Mg, Al, Si, Ti, Cr, Cu, Zn, Ge, Zr, Nb, Mo, Ag, In, Sn, W, Pt, Au, and Bi Targets

The results of experimental investigations of the angular distributions during magnetron sputtering of Mg, Al, Si, Ti, Cr, Cu, Zn, Ge, Zr, Nb, Mo, Ag, In, Sn, W, Pt, Au, and Bi targets in argon at a constant current are presented. The operating conditions during the experiments corresponded to the values typical of industrial sputtering equipment. The angular distribution of the material flow was calculated based on the measured thickness of the coating deposited on two flexible ribbon substrates. These substrates were fixed in place on a substrate holder in the form of two crossed half-rings that were equidistant from the center of the magnetron target (the curvature radius was 100 mm). The influence of the magnitude and shape of the magnetic field near the surface of the sputtered cathode on the angular distribution was also investigated. The results can be used as the source data for calculating the profile of the coating during magnetron sputtering.

Observation of the Magneto-Thomson Effect.

We report the observation of the higher-order thermoelectric conversion based on a magneto-Thomson effect. By means of thermoelectric imaging techniques, we directly observed the temperature change induced by the Thomson effect in a polycrystalline Bi_{88}Sb_{12} alloy under a magnetic field and found that the magnetically enhanced Thomson coefficient can be comparable to or even larger than the Seebeck coefficient. Our experiments reveal the significant contribution of the higher-order magnetothermoelectric conversion, opening the door to "nonlinear spin caloritronics."

Enhanced Thermoelectric Performance of Bi0.46Sb1.54Te3 Nanostructured with CdTe.

Cd-containing polycrystalline Bi0.46Sb1.54Te3 samples with precisely controlled phase composition were synthesized by conventional melting-quenching-annealing technique and a melt-spinning method. The pseudo ternary phase diagram for Cd-Bi/Sb-Te in the region near Bi0.46Sb1.54Te3 was systematically studied. Cd serves as an acceptor dopant contributing holes, whereas for samples doped with CdTe, the combined effects of the substitution of Sb/Bi with Cd and the formation of Sb/BiTe antisite defects leads to the increase in hole concentration. Moreover, upon doping with Cd, the lattice thermal conductivity decreases significantly owing to the intensified point defect phonon scattering. The sample with Cd content of 0.01 attains the maximum ZT of 1.15 at 425 K. The utilization of melt-spinning method brings about the in situ nanostructured CdTe and grain size refinement, which further reduce the lattice thermal conductivity while preserving excellent electrical performance. As a result, a higher ZT of 1.30 at 425 K is realized with CdTe content x = 0.005.

Temperature and magnetic field dependences of galvanomagnetic properties of Bi1−xSbx solid solutions in the range x = 0–0.25

Abstract Bi1–xSbx solid solutions are the best n-type thermoelectric materials for use at temperatures ≤200 K. An important parameter determining material’s figure of merit is charge carrier concentration. To determine it correctly, one should carry out measurements in a weak magnetic field. On the basis of the magnetic field dependences of the Hall coefficient and magnetoresistance, the dependences of the weak magnetic field boundary Bc on composition (x = 0–0.25) and temperature (T = 77–300 K) for polycrystalline Bi1–xSbx alloys were plotted. It was established that the Bc(x) dependences exhibit a non-monotonic behavior which is attributed to the existence of electronic phase transitions.

Growth of dilute quaternary alloy InPNBi and its′ characterization

Abstract InPNBi alloy semiconductor is grown for the first time on InP substrates by liquid phase epitaxy (LPE) technique by adding minute amounts of polycrystalline InN and Bi to the growth melt (upto 3 wt% of InN and 3 wt% of Bi in the melt). Energy dispersive X-ray (EDX) spectroscopy shows the presence of Bi and N in the material. Crystalline quality of the layer and the lattice contraction and dilation with respect to the substrate are demonstrated by high resolution X-Ray diffraction (HRXRD) measurements on layers containing N and Bi in different ratios. This result is qualitatively substantiated from the values of N and Bi contents obtained from the analysis of the X-ray photoelectron spectroscopy (XPS) measurements performed on each layer. XPS further provides details of the N and Bi bonding with In in the lattice. Raman spectroscopy measurements are done on the layers to investigate the different vibrational modes associated with the constituent elements and their bonds. 10 K photoluminescence (PL) indicate band gap reduction in the alloy upto 63 meV due to the incorporation of N and Bi atoms at the P sites of the InP lattice.

Origin of linear magnetoresistance in polycrystalline Bi films

The linear magnetoresistance (LMR) effect is an interesting topic due to its potential practical applications in magnetoelectronic sensors and magnetic random-access memories. We report the LMR in polycrystalline Bi thin films synthesized by the molecular beam epitaxy method. Though the present films are complex and disordered, semimetal to semiconductor transition is observed due to the quantum size effect. The LMR of the topologically protected surface state dominated two-dimensional transport can be mainly described by the theory of mobility fluctuation based on the Parish-Littlewood (PL) model. In addition, when the temperature is below 10 K, the LMR is originated from the linear energy dispersion based on the quantum model as the supplement of the PL model. The combination of the quantum and PL model may shed light on the LMR essence of polycrystalline Bi films.

Effect of the Crystal Alignment and Grain Size on the Thermoelectric Properties of Bi <sub>0.4</sub>Sb <sub>1.6</sub>Te <sub>3</sub> Sintered Materials

Sintered polycrystalline Bi0.4Sb1.6Te3 thermoelectric materials with various degrees of crystal alignment and grain sizes were prepared by pulse-current sintering under cyclic uniaxial pressure at sintering temperatures of 350–425 °C for holding times of 0–60 min to clarify the relationship between the microstructure and the thermoelectric properties. The degree of crystal alignment was enhanced with an increase of both the sintering temperature and holding time, and grain growth was also confirmed in the high temperature or long-time sintering process. The thermoelectric properties were measured perpendicular to the pressing direction, which corresponds to the crystal alignment direction. The electrical resistivity decreased and the thermal conductivity slightly increased with increasing sintering temperature and holding time. As a result, the figures of merit of the crystal-aligned samples sintered at high temperatures or for long holding times tended to reach 0.9–1 with large power factors because of the small electrical resistivity. The relationships between the quantified microstructure parameters and thermoelectric properties are discussed. The electrical resistivity decreased with increasing degree of crystal alignment and it saturated at a certain degree of crystal alignment, indicating that perfect crystal alignment is not necessary to obtain the lower limit of the electrical resistivity. Conversely, no significant change of the lattice thermal conductivity was observed in the grain size range 0.6–9.7 μm. This means that the lattice thermal conductivity of crystal aligned Bi0.4Sb1.6Te3 is almost independent of the degree of crystal alignment and grain size in the measured range.

Investigation of growth characteristics and semimetal-semiconductor transition of polycrystalline bis-muth thin films.

The preferred orientation growth characteristics and surface roughness of polycrystalline bis-muth (Bi) thin films fabricated on glass substrates using the molecular beam epitaxy method were investigated at temperatures ranging from 18 to 150°C. The crystallization and morphology were analyzed in detail and the polycrystalline metal film structure-zone model (SZM) was modified to fit the polycrystalline Bi thin film. The boundary temperature between Zone T and Zone II in the SZM shifted to higher temperatures with the increase in film thickness or the decrease of growth rate. Furthermore, the effect of the thickness and surface roughness on the transport properties was investigated, especially for Bi thin films in Zone II. A two-transport channels model was adopted to reveal the influence of the film thickness on the competition between the metallic surface states and the semiconducting bulk states, which is consistent with the results of Bi single-crystal films. Therefore, the polycrystalline Bi thin films are expected to replace the single-crystal films in the application of spintronic devices.

The composition and poling-dependent photovoltaic studies in ferroelectric (Bi1−xSrx)(Fe1−xTix)O3 thin films

The polycrystalline (Bi1−xSrx)(Fe1−xTix)O3 (x = 0.0, 0.05, 0.10, and 0.20) thin films were grown on Pt(111)/TiO2/SiO2/Si(100) substrates using chemical solution deposition technique. X-ray diffraction pattern revealed that pure BiFeO3 film is crystallized in rhombohedrally distorted crystal structure. However, the patterns for doped samples displayed a mixed-phase (rhombohedral + tetragonal) structure. The Raman studies revealed the emergence of B mode related to the tetragonal phase along with the modes corresponding to the rhombohedral phase in doped systems. The photovoltaic studies displayed a large photovoltaic response for the parent compound with an open-circuit voltage of 0.47 V. However, it showed a decrease in the photovoltaic response with an increase in composition x. The composition-dependent photovoltaic response could be correlated to the evolution of tetragonal phase fractions and the polarization. Additionally, the poling-dependent photovoltaic studies revealed the dominant role played by the polarization in comparison with the interface Schottky effect. This work gives an improved understanding of the ferroelectric photovoltaic mechanism and, therefore, may offer guidelines to design and optimize photovoltaic materials.

Electrical properties and fluctuation induced conductivity studies of Bi-based superconductors added by CuS nanoparticles synthesized through the aqueous route

The effect of copper sulfide (CuS) nanoparticles synthesized by aqueous route on the electrical transport and on the fluctuation induced conductivity of polycrystalline (Bi,Pb)2Sr2Ca2Cu3Oy (denoted Bi-2223) was reported. The global critical current densities versus temperature, Jct(T), at self and applied magnetic field was analyzed within the collective pinning model. The electrical resistivity versus temperature, ρ(T), above the mean-field temperature Tc was analyzed using Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) models. Different fluctuation regimes indicated by short-wave region (SWR), three-dimensional (3D), two-dimensional (2D), one-dimensional (1D), and critical region (CR) fluctuations were identified. The zero-temperature coherence length, the effective layer thickness, the critical magnetic fields, and the critical current densities are determined. It was found that samples sintered with an additional amount of CuS nanoparticles (< 0.4 wt%) exhibit higher upper critical magnetic fields and critical current densities compared to the pure one and the highest values of these parameters are obtained in the 0.2 wt% CuS added sample. Consequently, the addition of CuS nanoparticles could introduce strong pinning centers that contribute to the decrease of magnetic vortex motion which enhances the flux pinning capacities and the transport abilities inside the Bi-2223 system.

Bi substituted YIG ceramics isolator for optical communication

We have succeeded in synthesizing transparent (BixY3-x)Fe5O12 [x = 0–1.1] ceramics by reactive sintering method for the first time in the world. The transmission spectrum of Bi-doped YIG showed characteristics comparable to the Bi:Gd3Fe5O12 single crystal produced by LPE method. The obtained Bi:YIG ceramic was uniformly composed of grains around below 5 μm. Residual pores, secondary phases and grain boundary phases were not detected. The distribution of Bi, Y, and Fe in this material was extremely uniform for up to x = 0.4, but a rather high concentration of Bi at grain boundaries was detected by HR-TEM-EDS analysis for x = 0.8. The Faraday rotation angle linearly increased with the Bi content, and the Faraday rotation angle per atomic % of Bi was −31.2 deg./cm at 1550 nm, and this value was similar to the (Bi1.1Gd1.9)Fe5O12 single crystal produced by LPE method. In addition to LPE method which requires a seed substrate (Gd3Ga5O12) and a steep temperature gradient, it was demonstrated in this work that Bi-doped iron garnet can be synthesized by solid-state reactive sintering method, and also confirmed that the magneto-optical performance of the polycrystalline Bi:YIG ceramics was equivalent to single crystal.