Nominal Composition Bi Research Articles

Influence of La3+ Substitution on Electrical and Photocatalytic Behavior of Complex Bi2Sn2O7 Oxides

Pyrochlore-type Bi2–xLaxSn2O7 (0.0 ≤ x ≤ 0.20) system has been explored for its facile synthesis and electrical and photocatalytic functionalities. The highly distorted α-polymorph of Bi2Sn2O7 was synthesized, and successive La3+ substitutions were found to increase the lattice symmetry. Electric field dependent polarization measurements showed the ferroelectric hysteresis loop for pure Bi2Sn2O7 for the first time, and La3+ substitution was found to have a bearing on the ferroelectric properties with concomitant increase in leakage current. Temperature-dependent polarization studies were also performed on various nominal compositions. Diffuse reflectance spectroscopy established the tenability of the band gap as the function of La3+ content (2.5–3.0 eV). In order to explore the multifunctionality of this unique bismuth-containing system, the photocatalytic dye degradation of rhodamine B was investigated with Bi2–xLaxSn2O7 (0.0 ≤ x ≤ 0.20) system in both UV and visible regions. The variation in band gap introduced La3+ substitution significantly enhanced the photocatalytic behavior of bismuth stannate for rhodamine B degradation. The rate constant for the nominal composition Bi1.85La0.15Sn2O7 (17.6 × 10–2 min–1) is 6-fold the value for the pure Bi2Sn2O7 (2.75 × 10–2 min–1). The degradation profiles of rhodamine B in the UV and visible regions showed that dye degradation proceeds through different mechanisms which are discussed. The present study attempts to give an insight into the variation in electrical and photocatalytic properties and relate them to changes in structure. Bi2–xLaxSn2O7 (0.0 ≤ x ≤ 0.20) system is being proposed here as multifunctional candidates for lead-free electrical materials and efficient photocatalyst in the UV and visible regions.

Mechanical Properties of BSCCO Superconductor by Oliver–Pharr Method and Work of Indentation Approach

Polycrystalline superconducting Bi-Pb-Gd-Sr- Ca-Cu-O bulk samples with nominal composition Bi1.7Pb0.3−xGdxSr2Ca3Cu4O12+y (x = 0.00, 0.01, 0.05) were produced by the melt quenching method. The mechan- ical properties of the samples were characterized by depth sensing indentation technique under different peak loads ranging from 200 to 1800 mN. The experimental data were comparatively analyzed by the Oliver-Pharr method and a work of indentation approach. It was found that the work of indentation approach gave more reliable results because of the reducing pile-up effect. The results implied that both microhardness and reduced elastic modulus increased with increasing Gd substitution.

Bulk intergrowth of a topological insulator with a room-temperature ferromagnet

We demonstrate that the layered room-temperature ferromagnet Fe${}_{7}$Se${}_{8}$ and the topological insulator Bi${}_{2}$Se${}_{3}$ form crystallographically oriented bulk composite intergrowth crystals. The morphology of the intergrowth in real space and reciprocal space is described. The basal planes of Bi${}_{2}$Se${}_{3}$ and Fe${}_{7}$Se${}_{8}$ are parallel in the micron-scale intergrowth, and hence the good cleavage inherent to the bulk phases is retained. Both phases in the intergrowth crystals display their intrinsic bulk properties: the ferromagnetism of the Fe${}_{7}$Se${}_{8}$ is anisotropic, with the magnetization easy axis in the plane of the crystals, and angle-resolved photoemission spectroscopy characterization shows that the topological surface states remain present on the Bi${}_{2}$Se${}_{3}$ and that a gap can be observed in the surface state dispersion. Crystals of nominal composition Bi${}_{2\ensuremath{-}x}$Fe${}_{x}$Se${}_{3}$ are shown to be bulk intergrowths of the two phases Bi${}_{2}$Se${}_{3}$ and Fe${}_{2}$Se${}_{3}$. Significant solubility of Fe in Bi${}_{2}$Se${}_{3}$ is not observed.

Thermal treatment of superconductor thin film of the BSCCO system using domestic microwave oven

In this work, we report the preparation of a superconductor thin film of the BSCCO system using a good quality powder with nominal composition Bi1.8Pb0.4Sr2CaCu2Ox which was thermally treated using a domestic microwave oven (2.45 GHz, 800W). This film was grew on a single crystal of LaAlO3 (100) substrate and exhibited a crystalline structure with the c-axis perpendicular to the plane of the substrate. An onset superconducting transition temperature was measured at 80K.

Preparation and Characterization of Hot-Pressed and Sintered BiPbSrCaCuO Superconductor

Powder compacts of the system Bi2–xPbxSr2Ca2Cu3Oy with 0 ≤ x ≤ 0.5 molar ratio using both techniques; isothermal hot pressing and the solid state reaction (sintering). The XRD of the hot pressed powder compacts of the nominal compositions Bi2–xPbxSr2Ca2Cu3Oy showed 2212 and 2223 phases. The resistivity temperature variations belonging to the composition Bi1.8Pb0.2Sr2Ca2Cu3Oy showed metal-superconducting transition at Tons = 143 K for the annealed sample for 24 h. The annealed nominal composition Bi1.5Pb0.5Sr2Ca2Cu3Oy for 18 h showed metal to superconducting transition at 80 K.

Effect of Different Calcination Process and Gd<sub>2</sub>O<sub>3</sub> as Impurities on the Different Phases of Bi-Based Superconductor

In this research two samples of a nominal composition Bi1.6Pb0.4Sr2Ca2Cu3Ox were prepared by the solid state reaction method, using two different routes. Codes A and B are used to refer to the two samples. In preparing sample A, the standard method for calcination was used, while for sample B, the SrCO3 and CaCO3 were calcinated at 1100℃ for 3 h. Calcination was done separately on SrCO3 and CaCO3 in order to eliminate CO2. Then after mixing and grinding, the powder mixtures of Bi2O3, CuO, PbO, SrO and CaO were calcinated at 840℃ for 70 h. Also, the samples (samples C) of nominal compositions Bi1.6Pb0.4Sr2Ca2Cu3Ox+ % x Gd2O3 (% x = 0, 3, 5, 7 and 9) have been synthesized by this method. The XRD and SEM results show that addition of Gd2O3 helps to increase the amount of Bi-2212 phase, while alternative calcination process improves the formation of the Bi-2223 phase. In addition, the AC susceptibility measurements confirm the XRD and SEM results.

Synthesis and Magnetic Properties of (Bi, Pb)2Sr2Ca2Cu3O10+δ Superconductor

The sample of nominal composition Bi1.6Pb0.4Sr2Ca2Cu3O10+δ was prepared by the solid-state reaction method and systematically studied for their magnetic properties. The phase identification/gross structural characteristics of synthesized (HTSC) materials explored through powder X-ray diffractometer reveals that all the samples crystallize in orthorhombic structure with lattice parameters a=5.4054 Å, b=5.4111 Å and c=37.0642 Å. The critical transition temperature (T c ) measured by the standard four-probe method has been found to decrease from 108 K. The surface morphology investigated through scanning electron microscope and atomic force microscopy (SEM and AFM) results that voids and grains size increases of the Bi-2223 sample. The structural/microstructural characteristics (TEM) of Bi-based cuprate HTSC phase exhibit curious structural features including the occurrence of super lattice modulation along the b direction and c direction that have been observed. The presence of this streak reveals the presence of planar disorder representing faults in the stacking of CuO2 planes. The variation of magnetization with temperature (M–T curve) of the same Bi-based HTSC materials was measured by cooling the sample in zero fields (ZFC) and an applied field of 0.05T (here after referred as FC).

Phase equilibria and electrical properties of pyrochlore and zirconolite phases in the Bi2O3–ZnO–Ta2O5 system

The complete subsolidus phase diagram of the system Bi2O3–ZnO–Ta2O5, including cubic pyrochlore and monoclinic zirconolite phases, has been determined at 950–1050 °C. Through systematic heat treatment and X-ray diffraction of over 100 compositions, the layout of compatibility triangles (both 2-phase and 3-phase) and single phase solid solution areas has been determined. Pyrochlore and zirconolite phases have ideal nominal compositions Bi1.5Zn1.0Ta1.5O7 and Bi2(Zn1/3Ta2/3)2O7 respectively, but both form solid solution areas. The sintering condition of pyrochlore pellets has been optimised to obtain high density ceramics with minimal weight loss: optimised condition is 1100 °C for pellets covered with sacrificial powder. Permittivity, ɛ′ dielectric loss and temperature coefficient of capacitance, TCC, of single phase materials were measured using impedance spectroscopy; ɛ′ and TCC show little variation with composition but the losses are higher for Zn-deficient compositions.

The Effect of Mn Substitution on Properties of Bi1.6Pb0.4Sr2Ca2−x Mn x Cu3O y Superconductors

The effects of Mn substitution on the physical properties and structural characteristics of Bi1.6Pb0.4Sr2Ca2Cu3−xMnxOy (Bi-2223) superconductor system have been studied. For this, the samples of nominal composition Bi1.6Pb0.4Sr2Ca2Cu3−xMnxOy (x=0.00, 0.10, 0.15 & 0.20) was prepared by the solid-state reaction method. It has been found that the effects of Mn substitution favor the formation of Bi-2223 phases. The phase identification/gross structural characteristics of synthesized (HTSC) materials explored through powder X-ray diffractometer reveals that all the samples crystallize in orthorhombic structure with lattice parameters (a=5.4918 A, b=5.4071 A, and c=37.0608 A) up to Mn concentration of x=0.20. The critical transition temperature (Tc) measured by standard four probe method has been found to depress from 108 K to 70 K and transport current density (Jc) has been increased from 4.67×102 to 3.52×103 A cm−2 as Mn content (x) increases from 0.00 to 0.20. The surface morphology investigated through scanning electron microscope and atomic force microscopy (SEM and AFM) results that voids and grains size increases as the Mn concentration increases besides the nanosphere like structures on the surface of the Mn doped Bi-2223 sample.

Effects of Bi Content on the Ferroelectric Properties of BiFeO3 Thin Films

Two polycrystalline BiFeO3 thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by using pulsed laser deposition from nominal composition Bi1.0FeO3 and Bi1.1FeO3 targets. X-ray diffraction results confirmed that different impurity phases were formed in the Bi1.0FeO3 and the Bi1.1FeO3 thin films. The preferred orientation of the Bi1.0FeO3 thin films is the direction while that of the Bi1.1FeO3 thin films is the direction. The values of the remnant polarization (2Pr) of the Bi1.0FeO3 and the Bi1.1FeO3 film capacitors were 49 μC/cm 2 at an applied electric field of 500 kV/cm and 40 μC/cm at 467 kV/cm. A similar leakage current property was observed in both films.

Comparison for Thermoelectric Properties of BiTe Based Semiconductor Processed by the Mechanical Alloying and the High Pressure Torsion after Melt Grown by the Vertical Bridgman Method

Bi 2 Te 3 -related thermoelectric semiconductors were prepared by the mechanical alloying (MA) and the vertical Bridgman (VBM) - High Pressure Torsion (HPT) methods. Structures and electric properties of these alloys were then investigated. These samples had a nominal composition of Bi 0.5 Sb 1.5 Te 3.0 with 0.07 mass% excess Te. The MA sample was sintered into a compact after mechanical alloying by hot-pressing while the VBM - HPT sample was subjected by HPT after being cut into a disk from a melt-grown ingot by the vertical Bridgman method (VBM). The orientation factors of the MA and VBM - HPT samples were 0.054 and 0.525, respectively, indicating that the preferred orientation was formed by VBM - HPT. Average grain sizes of both samples were approximately 2 μm. By estimating the slope of carrier mobility versus temperature the carrier scattering factor of the MA and VBM - HPT samples were estimated to be -2.8 and -1.4. These values are indicative of carrier scatterings by acoustic phonons and by the interaction between acoustic and optical phonons, respectively. The maximum power factor obtained for the isotropic MA sample was 4.1 × 10 -3 W m -1 K -2 at 310 K and this was about twice the 2.1 × 10 -3 W m -1 K -2 at 440K obtained for the anisotropic VBM - HPT sample.

Thermoelectric Properties and Scattering Factors of Finely Grained Bi<SUB>2</SUB>Te<SUB>3</SUB>-Related Materials Prepared by Mechanical Alloying

Fine grained samples with a nominal composition of Bi 0.5 Sb 1.5 Te x (x = 3.0 to 3.4) were prepared by mechanical alloying (MA). Average grain sizes were found to range from 1.0 to 2.1 μm. Tellurium precipitation at x = 3.1 was observed by scanning electron microscopy (SEM), X-ray diffraction and differential thermal analysis (DTA). Electrical conductivity as well as Hall and Seebeck coefficients were measured from 300 to 470 K. Using the relationship between Hall mobility and temperature, carrier scattering factors of the Bi 0.5 Sb 1.5 Te x samples were estimated to range from r = -0.9 to -2.0. The thermal conductivities of the samples were found to range from 0.94 to 1.00 Wm -1 K -1 at room temperature. Excess tellurium was recognized to be responsible for the decrease in thermal conductivity. The Lorenz number and the carrier component of thermal conductivity were calculated from the scattering factor and the Fermi integral. The phonon component of thermal conductivity was dominant in the Bi 0.5 Sb 1.5 Te x samples. The Seebeck coefficient of the Bi 0.5 Sb 1.5 Te x samples was higher than that from the available data which means that the absolute scattering factor of the Bi 0.5 Sb 1.5 Te x samples was large. A maximum figure of merit of 7.02 x 10 -3 K -1 was obtained at 310 K for the Bi 0.5 Sb 1.5 Te 3.1 sample. This high figure of merit results from an enhanced Seebeck coefficient that is due to an increased absolute scattering factor. High thermoelectric performance can, therefore, be established by a reduction in the phonon component of the thermal conductivity and also by an enhanced Seebeck coefficient, which results from an increased absolute scattering factor for finely grained Bi 0.5 Sb 1.5 Te x samples that were prepared by MA.

The Effect of AgNO3 Addition on the Formation and Superconducting Properties of the Bi2223 Phase

Superconducting samples with nominal composition Bi1.66Pb0.34Sr2Ca2Cu2Ox–Ag are prepared by the solid-state reaction method. The samples are characterized by X-ray diffraction and DC electrical resistivity. According to X-ray diffraction patterns of specimens, the highest amount of Bi-(2223) phase along with the minimum amount of Bi-(2212) phase and minimum effect on the crystal structure was accessible in the sample with 10 wt. % of AgNO3 content. The standard four-probe technique is applied to measure the DC electrical resistivity in the temperature range from 77 to 250 K and the influence of different Ag contents on the normal phase resistance, transition width and critical temperature Tc has been investigated comparatively.

Formation of proposed superconducting phases in nominal compositions Bi1.7Pb0.3Sr2Ca x − 1Cu x O y (x = 4, 5, 7, 9) on the basis of amorphous precursors, obtained under the action of concentrated sunlight

The possibility of obtaining superconducting phases in compositions Bi1.7Pb0.3Sr2Cax − 1CuxOy (x = 4, 5, 7, 9) with increased Ca and Cu content from amorphous precursors that are obtained under the action of concentrated sunlight is investigated. It is established that the temperature of formation of the superconducting phases decreases with increase of the Ca and Cu content.

Texture of bismuth telluride-based thermoelectric semiconductors processed by high-pressure torsion

P-type Bi 2Te 3-based thermoelectric semiconductors were prepared, having a grain-refined microstructure and a preferred orientation of anisotropic crystallographic structure. Disks with a nominal composition of Bi 0.5Sb 1.5Te 3.0 were cut from an ingot grown by the vertical Bridgman method (VBM) and deformed at 473 K under a pressure of 6.0 GPa by high-pressure torsion (HPT). The crystal orientation was characterized by X-ray diffraction. The microstructures were characterized using optical microscopy and scanning electron microscopy (SEM). It was found that the HPT disks had a fine and preferentially oriented grain compared to that of the VBM disks. Further, the power factor of the HPT disks was about twice as large as that of the VBM disks. These results indicate that HPT is effective in improving the thermoelectric properties of Bi 2Te 3-based thermoelectric semiconductors.

Electrothermal performance and growth of single phase in barium doped Bi-2223 high-Tc superconductors

Solid state reaction method was used to synthesize the high-Tc superconducting material with nominal composition Bi1.6Pb0.4Sr1.6Ba0.4Ca2Cu3Oy. This paper investigates the associations among macroscopic physical properties and features at atomic level for the prepared samples. The samples were preliminary analyzed by dc electrical resistivity and ac magnetic susceptibility. After that thermal transport, electrothermal conductivity and thermoelectric properties all as a function of temperature (from room down to liquid nitrogen temperature) were measured. X-ray diffraction studies were also done for structural analysis. All the above measurements showed that in the samples, there exists almost a single high- Tc phase with Tc,0 ∼ 110±1K. The lattice constants of the material were determined by indexing the diffraction peaks. Samples were investigated for thermal transport properties, i.e. thermal conductivity, thermal diffusivity and heat capacity per unit volume. Thermal transport properties were measured by a newly developed and calibrated Advantageous Transient Plane Source method. Simultaneous measurement of thermal conductivity and thermal diffusivity made it possible to estimate specific heat and the Debye temperature TD. Thermoelectric power (Seebeck Coefficient) and electrothermal conductivity were also measured with a recently developed and attuned apparatus. Using dc electrical resistivity, thermal conductivity and thermoelectric power, the Figure of merit factor was also calculated.

Thermoelectric Properties of Bi<SUB>2</SUB>Te<SUB>3</SUB>-Related Materials Finely Grained by Mechanical Alloying and High Pressure Torsion

Bi 2 Te 3 -related thermoelectric semiconductors were prepared by the mechanical alloying (MA) and the vertical Bridgman (VBM)-High Pressure Torsion (HPT) methods. Structures and electric properties of these alloys were then investigated. These samples had a nominal composition of Bi 0.5 Sb 1.5 Te 3.0 with 0.07 mass% excess Te. The MA sample was sintered into a compact after mechanical alloying while the VBM-HPT sample was deformed by HPT after being cut into a disk from a melt-grown ingot by the vertical Bridgman method (VBM). The orientation factors of the MA and VBM-HPT samples were 0.054 and 0.525, respectively, indicating that the preferred orientation was formed by VBM-HPT. Average grain sizes of both samples were approximately 2 μm. The VBM-HPT sample was shown low electrical conductivity than the MA one in spite of the high orientation factor. By estimating the slope of carrier mobility versus temperature the carrier scattering factor of the MA and VBM-HPT samples were estimated to be ―1.3 and +0.1. These values are indicative of carrier scatterings by acoustic phonons and by the interaction between acoustic and optical phonons, respectively. The maximum power factor obtained for the isotropic MA sample was 4.1 x 10 -3 W m -1 K -2 at 310 K and this was about twice the 2.1 × 10 -3 W m -1 K -2 at 440 K obtained for the anisotropic VBM-HPT sample.

Thermal Conductivity and Thermoelectric Power of Vanadium-Substituted Bi-Based (2223) High-T c Superconductor as a Function of Temperature

Superconducting samples with nominal composition Bi1.3V0.3Pb0.4Sr2Ca2Cu3Oδ are prepared by the solid state reaction method. The samples are characterized by X-ray diffraction, scanning electron microscopy, DC electrical resistivity, critical current density, AC magnetic susceptibility, thermal conductivity and thermoelectric measurements. The room temperature X-ray diffraction pattern of the sample indicated the presence of large amount of Bi-(2223) phase along with minor amount of Bi-(2212) phase. The standard four-probe technique is applied to measure DC electrical resistivity in the temperature range from 300 to 77 K. The onset temperature Tc (onset) and zero resistivity critical temperature Tc (R=0) are found to be 112±1 K and 106±1 K, respectively. The low field AC magnetic susceptibility is also measured as a function of temperature. Thermal conductivity and thermoelectric power of large disc-shaped cylindrical samples are measured as a function of temperature from 300 to 77 K. The increase in thermal conductivity is observed below and above Tc (R=0). The estimation of the resistivity change due to scattering by phonons and impurities has been discussed.

Thermal and electrothermal characterization of bismuth based high-Tc superconductors

Abstract This paper investigates the relationships among macroscopic physical properties and features at atomic level for the high- T c superconducting material with nominal composition Bi 1.6 Pb 0.4 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O y , which was prepared by a solid-state reaction method. The samples were analyzed by dc electrical resistivity, ac susceptibility, thermal transport, electrothermal conductivity and thermoelectric properties all as a function of temperature (from room down to LN 2 temperature). Room temperature X-ray diffraction studies were also done. All the above measurements showed that in the samples, there exists almost a single high- T c phase with T c,0 ≃ 110 ± 1 K. The lattice constants of the material were determined by indexing the diffraction peaks. Samples are investigated for thermal transport properties, i.e. thermal conductivity, thermal diffusivity and heat capacity per unit volume, by an advantageous transient plane source method. Simultaneous measurement of thermal conductivity and thermal diffusivity makes it possible to estimate specific heat and the Debye temperature Θ D . Thermoelectric power (Seebeck coefficient) and electrothermal conductivity is also measured with a newly developed and calibrated apparatus. Using electrical resistivity, thermal conductivity and thermoelectric power, the Figure of merit factor was calculated.

The Influence of Acceptor Doping on the Structure and Electrical Properties of Sol-Gel Derived BiFeO3 Thin Films

Bismuth Ferrite (BFO) films doped with strontium resulting in a nominal composition of Bi 1−x Sr x Fe 1 O 3 (x = 0–0.15) were fabricated using a sol-gel process on Pt/TiO 2 /SiO 2 /Si substrates by rapid thermal annealed in air at 700°C. A decrease in the grain size (from 1 μm to 90 nm) with increasing Sr concentration from 0 to 15% was observed, coupled with the degradation of columnar grain growth. X-ray diffraction and raman scattering showed evidence of a structural change from rhombohedral to pseudocubic with increasing Sr concentration. Leakage measurements revealed that films with Sr acceptor doping showed increased leakage compared to pure BFO, however the film leakage did not increase with increasing acceptor concentration due to microstructural modifications.