Polycrystalline Bi Research Articles

Simulation of polycrystalline bismuth films Seebeck coefficient based on experimental texture identification

Seebeck coefficient values measured for textured polycrystalline Bi films have been compared with numerically computed ones. The proposed computation procedure requires crystallographic texture mapping and values of single-crystalline transport coefficients as input data. The comparison of computed and measured Seebeck coefficients allowed determining the factors affecting films' transport properties except of crystalline texture. Two particular cases are considered: when the film properties are affected only by texture and when they depend on texture and grain size simultaneously.

Role of preparation conditions of Bi-2223 ceramic materials and optimization of Bi-2223 phase in bulk materials with experimental and statistical approaches

This study deals with the determination of optimum preparation conditions (press load, annealing temperature and time) for the Bi-2223 superconducting compound with the aid of both the experimental methods regarding dc resistivity, transport critical current density and powder X-ray diffraction measurements and statistical approaches including response surface explorer based on Box–Behnken designs for the first time. It is found that the Bi-2223 polycrystalline compound prepared under 300 MPa pressure load at 840 °C for 48 h presents the highest formation of Bi-2223 phase due to the considerable elimination of the impurity scattering and lattice strain in the crystal structure. On the other hand, the sample prepared at 860 °C under 350 MPa for 48 h exhibits the worst characteristic features of high Tc-phase as a consequence of the enhancement in local structural distortions, dislocations, defects and disorders in the Cu–O2 consecutively stacked layers. Thus, the latter condition causes to both the degradation in amplitude of pair wave function (decrease in the overlapping of Cu 3d and O 2p functions) and metastability due to the reduction of hole trap energy. In this respect, the best material displays the largest Tconset of 110.63 K and Tcoffset of 108.46 K values while the worst material obtains the smallest values (Tconset of 95.45 K and Tcoffset of 45.32 K). Similarly, the maximum Jc value of 818 A/cm2 is experimentally observed for the best compound whereas the worst sample obtains the smallest value of 112 A/cm2. The decrement in the Jc parameter is attributed to the regression of intergrain coupling and flux pinning vortices in the Bi-2223 crystal structure due to the increment of misorientations and especially grain boundary weak-interactions in the crystal system. The XRD results also reveal that the combination of 300 MPa press load, 840 °C annealing temperature and 48 h annealing time for the preparation condition promotes seriously the high Tc-phase as a consequence of the enhancement in the average crystallite size and lattice parameter c or decrement in the a-axis length. Accordingly, the best material obtains the largest c-axis length of about 37.22 Å and average grain size of 71.4 nm but the smallest lattice parameter a of about 5.29 Å. At the same time, the surface response designs of statistical analyses show that the optimum preparation conditions are defined to be 306.5657 MPa press load, 840 °C annealing temperature and 48 h annealing time to maximize the high Tc-phase (with the maximum Tconset,TcoffsetandJc parameters.

Synthesis and microwave dielectric behavior of (Bi1−xPbx)NbO4ceramics

Ceramic samples of (Bi[Formula: see text]Pbx)NbO4([Formula: see text], 0.025, 0.05, 0.10, 0.15, 0.20) with 0.75[Formula: see text]wt.% V2O5addition sintered at 920[Formula: see text]C, 940[Formula: see text]C and 960[Formula: see text]C are investigated. Pb is selected as a substitute for Bi[Formula: see text] in BiNbO4ceramics as it exists in two stable valence states of [Formula: see text]2 and [Formula: see text]4 and the average valency matches to that of Bi[Formula: see text]. The average Shannon radius (for octahedral coordination) of Pb[Formula: see text] (1.19[Formula: see text]Å) and Pb[Formula: see text](0.775[Formula: see text]Å) cations is 0.9825[Formula: see text]Å, which is similar to that of Bi[Formula: see text] ion (1.03[Formula: see text]Å). The dense ([Formula: see text]%) polycrystalline (Bi[Formula: see text]Pbx)NbO4samples fabricated mostly reveal orthorhombic (Pnna) phase ([Formula: see text]-BiNbO4, Sp. Gp. 52) by powder XRD. Presence of satellite Pb2Nb2O7phase, the amount of which is increasing with increase in Pb content, is also noticed. The microwave dielectric constant ([Formula: see text]) values of the niobates are found to increase from 42 to 71, whereas the quality factor (Qu.f) values are found to decrease from 5400 to 550 GHz with increasing substitution of Pb. The compositions so synthesized are important as hardly there are any microwave dielectric ceramics available with [Formula: see text].

Nanoindentation of single‐crystal Bi2Te3 topological insulators grown with the Bridgman–Stockbarger method

In this work, bismuth telluride (Bi2Te3) single crystals were grown from melted polycrystalline Bi–Te material using the Bridgman–Stockbarger method. Crystalline quality and surface chemistry were investigated through X‐ray diffraction analysis and X‐ray photoelectron spectroscopy. The mechanical properties were investigated by means of depth‐sensing nanoindentation tests carried out using the continuous stiffness measurement (CSM) technique. In turn, the distribution of material hardness and Young's modulus in the depth direction (i.e., perpendicular to the single crystal basal plane) were resolved and quantitative comparisons with the available data extracted from previous literature works were drawn. It is shown that the obtained single crystals are free of contaminants and/or oxide phases and that the mechanical properties lie between those reported in recent literature for Bi2Te3 polycrystalline thin films and 2D nanosheets.

Structure, phase diagram and magnetic properties of Bi1−xLaxFeO3 solid solution

A series of polycrystalline Bi1−xLaxFeO3 (0≤x≤1.00) solid solution were synthesized by sol–gel method. The effects of lanthanum concentration on the phase formation, phase transition and magnetic properties were studied. The XRD results displayed that there is a clear indication of structural modification and symmetry change brought about by La doping. At room temperature the crystal structure of the solid solution transforms from rhombohedral R3c (x≤0.15) to tetragonal P4mm (0.15<x<0.40), then to cubic Pm3¯m (0.40≤x<0.50), and finally to orthorhombic Pbnm (0.50≤x≤1.00). In situ high temperature X-ray powder diffraction studies reveal that phase transformations of the rhombohedral R3c and the cubic Pm3¯m to the orthorhombic Pbnm occur in the temperature regions of 680–730°C and 300–680°C,respectively. The phase transformations of the tetragonal P4mm to the cubic Pm3¯m occurs in the temperature region of 200–230°C, whereas the phase structure of orthorhombic Pbnm keeps unchanged below 850°C. Based on careful characterization of crystal structure and phase transition as a function of temperature, the phase diagram of the pseudo-binary BiFeO3–LaFeO3 system has been constructed. The phase diagram manifests that the Bi1−xLaxFeO3 (0≤x≤1.00) solid solution provides more options to tune the magnetism and multiferroism, as the crystal structures with polarity feature occur in a wide doping concentration of La (x≤0.30). We then selectively studied the magnetic properties of possible multiferroic phases, i.e. R3c and P4mm phases. The results revealed that both the magnetic remanence and the coercive field of Bi1−xLaxFeO3 (0<x≤0.30) increased with the La content.

Anomalous melting behavior of polycrystalline bismuth quenched at high temperature and high pressure

Under ambient conditions, bismuth (Bi) adopts a rhombohedral A7 structure, yet Bi treated at high temperature and high pressure (HTHP) has been proven to have derivative structural polytypes that coexist with the common A7 structure. This paper studies the melting behavior of HTHP-treated polycrystalline Bi using differential scanning calorimetry (DSC) and in situ transmission electron microscopy (TEM) measurements. The Bi samples quenched at a pressure of 2GPa and a temperature above 2000°C show an additional endothermic peak before the common melting peak of A7-Bi in the DSC curves. This is probably due to the high-temperature relaxation of the distorted A7 configuration. The samples maintain their initial morphology characteristics during repeated heating cycles, indicating the incomplete melting of distorted Bi polytypes.

The effect of quenching from different temperatures on Bi0.88Sb0.12 alloy

Structural, thermal, resistive and magnetic properties of melt quenched Bi0.88Sb0.12 alloys are reported. The samples are heated at three different temperatures, followed by rapid quenching in liquid nitrogen. Large temperature difference between liquidus and solidus lines, led to microscopic in-homogeneity in the alloy. The effect of quenching from different temperatures in polycrystalline Bi0.88Sb0.12 alloy has been studied. The parameters such as strain, unit cell volume, and resistivity are found to increase with temperature. Thermal variation of resistivity depicts non-monotonic temperature dependence. The total negative susceptibility increases and band gap of semiconducting Bi0.88Sb0.12 samples decreases with increasing temperature.

(110)-Textured Ca-doped BiFeO3 film on refined Pt(111) electrode layer on glass substrate at reduced temperature

Multiferroic and photovoltaic properties of polycrystalline Bi0.85Ca0.15FeO3 (BCFO) film on refined Pt(111) electrode buffered glass substrate have been studied. Optimized Pt(111) electrode layer having large grain size and smooth morphology enables the development of highly (110)-textured BCFO film at a temperature as low as 450°C. The prepared BCFO film has dense microstructure, fine grain size, and smooth surface morphology. Good ferroelectric properties with the remanent polarization (2Pr) of 108μC/cm2 and electrical coercive field of 405kV/cm are achieved. Improved ferromagnetic properties with magnetization of 9.2emu/cm3 and coercivity of 1250Oe are also attained. Significant PV properties with open-circuit photovoltage of 0.49V and the short-circuit photocurrent of 67.4μA/cm2 at illumination intensity of 228mW/cm2 are observed, which are comparable to BCFO ceramics or BFO epitaxial films.

Comparative study of structural and electrical properties of Pr and Ce doped BiFeO3 ceramics synthesized by auto-combustion method

Polycrystalline Bi1−xPr(Ce)xFeO3 ceramics (x = 0, 0.03, 0.05 and 0.10) were prepared by auto-combustion method using urea as a fuel. The influence of Pr(Ce) doping on structural, vibrational, morphological, dielectric and ferroelectric properties of BiFeO3 polycrystalline ceramics was investigated. From X-ray diffraction (XRD) and scanning electron microscopy measurements it was observed that Pr(Ce) doping generated a reduction of the crystallite (grain) size of BiFeO3 and contraction of the rhombohedral cell due to the increased compressive strain. The changes seen in the XRD and Raman spectra of 10% Pr(Ce)-doped samples, pointed to a probable appearance of orthorhombic (pseudotetragonal) crystal structure. The pristine BiFeO3 exhibited rounded shape, non-saturated ferroelectric hysteresis loop. The dielectric constant and dielectric loss have shown strong dispersion at lower frequencies, typical for conductive BiFeO3. Dielectric and ferroelectric properties at room temperature were improved with Pr doping. Concerning the Ce-doped samples, only the 3% Ce-doped sample exhibited a better shaped hysteresis loop and improved dielectric properties compared to the pristine BiFeO3. With further increase of Ce content the ferroelectric properties degraded.

Effect of the fabrication process on the electrical properties of polycrystalline Bi1.7Pb0.3Sr2Ca2Cu3O10

Polycrystalline Bi1.7Pb0.3Sr2Ca2Cu3O10 (BPSCCO) was successfully prepared by the sol–gel method, and excellent electrical properties were obtained by optimizing the preparation process. The crystalline structures of the samples were investigated by X-ray diffraction (XRD), and the temperature dependence of the resistance was measured using the standard four-probe method. A systematic comparison of the effects of different chelating agents on the preparation of polycrystalline BPSCCO was carried out. When glucose acid (GA) was employed as the chelating agent, high-quality polycrystalline BPSCCO (Tconset=114.3K) was obtained. Furthermore, the influence of the heat treatment procedure on polycrystalline BPSCCO was also investigated. The experimental results show that the crystallographic and electrical properties of the samples can be improved by controlling the processing conditions, including the calcination and sintering temperatures.

Enhancement in magnetic properties of Ba-doped BiFeO3 ceramics by mechanical activation

Here, we report on the enhancement in the magnetic properties of polycrystalline Bi1−xBaxFeO3 (x = 0.0, 0.05, 0.1 and 0.2) ceramic samples as a consequence of mechanical activated solid-state-reaction in comparison to standard solid-state-reaction processed samples. Our results suggest that mechanical activation has pronounced effect on the temperature of phase evolution as well as magnetic characteristics of Ba doped BiFeO3. The temperature, at which perovskite phase crystallizes is lower for mechanical activation assisted samples than for standard solid-state-reaction processed samples, attributed to pre-alloying during mechanical activation process. All the samples crystallize in a distorted perovskite structure with space group R3c and no structural change is found up to highest Ba doping. Mechanical activation also leads to significantly altered magnetic properties, particularly in higher Ba-doping samples which show about 50% increase in the magnetization and more than three fold increase in the coercive field. Local magnetic behavior investigated by 57Fe Mössbauer spectroscopy rules out any valence fluctuations of Fe and the hyperfine field corroborates the magnetization data.

Multiferroic properties of (Bi, Ca)FeO3 films on glass substrates

Effect of Ca substitution on the multiferroic properties of non-epitaxially grown polycrystalline Bi1−xCaxFeO3 (BCFO) films on refined Pt(111) electrode buffered glass substrates is studied. The structural analysis shows that a pure perovskite phase with isotropic orientation is present for BCFO films (x=0.05–0.15). The grain size and surface roughness are reduced with increasing x. Different from the BCFO ceramics, good ferroelectric properties with the remanent polarization (2Pr) of 91–124μC/cm2 and electrical coercive field (Ec) of 294–394kV/cm are obtained in BCFO polycrystalline thin films. Furthermore, the substitution of Ca2+ for Bi3+ effectively enhance the ferromagnetic properties with magnetization (Ms) of 5.9–8.2emu/cm3 and coercivity (Hc) of 1224–1258Oe. The ferromagnetic and ferroelectric properties and leakage behavior as functions of Ca content x are discussed.

Melting and solidification of bismuth antimony telluride under a high magnetic field: A new route to high thermoelectric performance

Imposing an intensity variable high static magnetic field during a traditional melting-solidification (MS) method has been used as a new method to prepare p-type bismuth antimony telluride thermoelectric materials in this work. On this basis, we present a systematic study of the nucleation, crystal orientation, microstructure, electrical and thermal transport properties of the obtained alloy ingots solidified under different magnetic field intensities. A c-axis alignment of bismuth antimony telluride in the direction perpendicular to the magnetic field, formation of BSTII nanorods, and a simultaneous optimization of the electrical and thermal transport properties have been observed. Consequently, an enhanced ZTmax=1.71 at 323K has been achieved in a polycrystalline Bi0.5Sb1.5Te3 sample solidified under a 2T magnetic field.

Strategies to unblock the n-GaAs surface when electrodepositing Bi from acidic solutions

Bismuth ultra-thin films grown on n-GaAs electrodes via electrodeposition are porous due to a blockade of the electrode surface caused by adsorbed hydrogen when using acidic electrolytes. In this study, we discuss the existence of two sources of hydrogen adsorption and we propose different routes to unblock the n-GaAs surface in order to improve Bi films compactness. Firstly, we demonstrate that increasing the electrolyte temperature provides compact yet polycrystalline Bi films. Cyclic voltammetry scans indicate that this low crystal quality might be a result of the incorporation of Bi hydroxides within the Bi film as a result of the temperature increase. Secondly, we have illuminated the semiconductor surface to take advantage of photogenerated holes. These photocarriers oxidize the adsorbed hydrogen unblocking the surface, but also create pits at the substrate surface that degrade the Bi/GaAs interface and prevent an epitaxial growth. Finally, we show that performing a cyclic voltammetry scan before electrodeposition enables the growth of compact Bi ultra-thin films of high crystallinity on semiconductor substrates with a doping level low enough to perform transport measurements.

Intergranular Coupling, Critical Current Density, and Phase Formation Enhancement of Polycrystalline Bi1.6Pb0.4Sr2Ca2Cu3O10−y Superconductors by α-Al2O3 Nanoparticle Addition

In this work, the effect of alumina (α-Al2O3) nanoparticle addition on the phase formation and superconducting properties of Bi1.6Pb0.4Sr2Ca2Cu3O10−y ((Bi,Pb)-2223) system has been investigated. Six samples with different alumina nanoparticle contents (0.0, 0.1, 0.2, 0.3, 0.5, and 1 wt % of the sample’s total mass) were prepared by conventional solid-state reaction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods have been used to study phase formation and microstructure of the prepared samples, respectively. Also, electrical resistivity and critical current density of the prepared samples were measured by four-probe technique. AC susceptibility of the samples has been measured by an LCR meter. XRD results showed that addition of small amounts of the alumina nanoparticles improves (Bi,Pb)-2223 phase formation significantly. Temperature dependency of AC susceptibility measurements revealed that addition of α-Al2O3 nanoparticles improves the intergranular coupling. The I-V measurements show that critical current density of samples increased from about 36 A/cm 2 for the alumina nanoparticle-free sample to about 107 A/cm 2 for the sample with 0.5 wt % α-Al2O3 nanoparticles.

Effect of Ba substitution on the multiferroic properties of BiFeO3 films on glass substrates

Effect of Ba substitution on the multiferroic properties of non-epitaxially grown polycrystalline Bi1−xBaxFeO3 (BBFO) films on refined Pt(111) electrode buffered glass substrates is studied. The structural analysis shows that a pure perovskite phase is present for BBFO films (x = 0.05-0.15), and (110) preferred orientation is developed for films with high x = 0.15. The grain size and surface roughness are reduced with increasing x. All studied BBFO films show desired ferroelectric and ferromagnetic properties. The good ferroelectric properties with the remanent polarization (2Pr) of 36-70 μC/cm2 and electrical coercive field (Ec) of 318-570 kV/cm are attained. On the other hand, the substitution of Ba2+ for Bi3+ in the A site of the BFO crystal structure can effectively enhance the ferromagnetic properties with magnetization (Ms) of 9.4-13.9 emu/cm3 and coercivity (Hc) of 1216-1380 Oe. The ferromagnetic and ferroelectric properties and leakage behavior as functions of Ba content x are discussed.

Phase Evolution, Magnetic, Optical, and Dielectric Properties of Zr‐Substituted Bi0.9Gd0.1FeO3 Multiferroics

Polycrystalline BiFeO3 (BFO) and Bi0.90Gd0.10Fe1−xZrxO3 (x = 0.0–0.10; BGFZx) ceramics were synthesized by solid‐state reaction method. Rietveld analysis of X‐ray diffraction patterns showed that BFO and BGFZx = 0.0 samples are stabilized in rhombohedral structure (space group R3c), whereas a small fraction of orthorhombic phase (space group Pn21a) is observed for BGFZx = 0.03–0.10 samples. Suppression and disappearance of some Raman modes indicated a structural phase transition with addition of Zr dopant at Fe site. Magnetic measurements exhibited weak ferromagnetic behavior of BGFZx samples with increasing Zr+4 concentrations. The insertion of Gd+3 ions at Bi+3 sites and nonmagnetic Zr+4 ions at Fe+3 sites in Fe–O–Fe network suppressed the spin cycloid structure of BFO which in turn enhanced the magnetization of these ceramics. Electron spin resonance spectra revealed the breaking of spin cycloid of BFO due to the development of free spins with addition of Zr+4 dopants at Fe sites. UV–Visible diffuse reflectance spectra showed one d–d crystal field transition and two charge‐transfer (C–T) transitions along with a sharp absorption of light in visible region for all samples. Almost frequency‐independent dielectric constant and dielectric loss along with very low values of dielectric loss indicated greatly improved dielectric properties for BGFZx = 0.03–0.10 samples.

Effect of rhombohedral to orthorhombic transition on magnetic and dielectric properties of La and Ti co-substituted BiFeO3

Polycrystalline Bi1−xLaxFe1−xTixO3 (x = 0.000–0.250) ceramics were synthesized by the tartaric acid modified sol–gel technique. It was observed that the co-substitution of La and Ti at Bi and Fe sites in BiFeO3 suppresses the impurity phase formation which is a common problem in the bismuth ferrite ceramics. The quantitative crystallographic phase analysis of x-ray diffraction pattern by employing Rietveld technique was performed with the help of FULLPROF program which suggests the existence of compositional driven crystal structure transition from rhombohedral (space group R3c) to the orthorhombic (space group Pbnm) symmetry. The oxygen octahedral tilt angle was found to be ∼13.82° for BiFeO3 (space group R3c) and decreases with the increase in co-substitution percentage. The structural transition breaks the spin cycloid structure in co-substituted BiFeO3 nanocrystallites and leads to canting of the antiferromagnetic spin structure. Hence, the remnant magnetization increases up to 10% of co-substitution and becomes 22 times that of BiFeO3. However, it decreases for higher co-substitution percentage due to significant contribution from the collinear antiferromagnetic ordering in the orthorhombic crystal symmetry. The dielectric constant attains a maximum for 10% of co-substitution.

Infrared surface polaritons on bismuth

Optical constants for evaporated bismuth (Bi) films were measured by ellipsometry and compared with those published for single crystal and melt-cast polycrystalline Bi in the wavelength range of 1 to 40 μm. The bulk plasma frequency ωp and high-frequency limit to the permittivity ε∞ were determined from the long-wave portion of the permittivity spectrum, taking previously published values for the relaxation time τ and effective mass m . This part of the complex permittivity spectrum was confirmed by comparing calculated and measured reflectivity spectra in the far-infrared. Properties of surface polaritons (SPs) in the long-wave infrared were calculated to evaluate the potential of Bi for applications in infrared plasmonics. Measured excitation resonances for SPs on Bi lamellar gratings agree well with calculated resonance spectra based on grating geometry and complex permittivity.

Enhanced open circuit voltage in photovoltaic effect of polycrystalline La and Ni co-doped BiFeO3 film

Photovoltaic (PV) effect of polycrystalline Bi 0.975 La 0.025 Fe 0.975 Ni 0.025 O 3 (BLFNO) film grown on Pt (111)/ Ti/SiO 2/ Si (001) substrate using sol–gel method has been investigated. The BLFNO film possesses good ferroelectric property and large twice-remanent polarization. It is found that PV response exhibited a strong dependence on the potential of top indium tin oxide (ITO) and bottom Pt electrode. The open circuit voltage is -0.67 V when the potential of ITO electrode is higher than that of Pt electrode and 0.45 V when the potential of ITO electrode is lower than that of Pt electrode. This can be interpreted by the variation of barrier heights at both ITO/BLFNO and BLFNO/ Pt interfaces.