Bismuth Substitution Research Articles

Photo-catalyst CoBixFe2−xO4–Bi2O3 nanocomposite: effect of bismuth substitution in magnetic properties of cobalt ferrite

CoBixFe2−xO4 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) powders were prepared via conventional ceramic method. Nano-crystalline cobalt ferrite doped bismuth and CoBixFe2−xO4–Bi2O3 (80–20 %) powders have been synthesized by ball milling route . The structural and magnetic properties of the samples were determined by X-ray diffraction, vibrating sample magnetometer and Faraday balance. X-ray analysis showed that the samples were cubic spinel. The addition of Bi3+ ions caused a decrease in magnetization, Curie temperature and the coercivity of the samples. The observed decreases in saturation magnetization and coercivity are explained on the spin-glass-like surface layer on the nanocrystalline cobalt–bismuth ferrite and magnetic anisotropy, including magneto-crystalline and strain induced anisotropies during ball-milling processing; respectively. The photo catalytic behaviour of CoBixFe2−xO4–Bi2O3 nanocomposites was evaluated using the degradation of three various azo dyes under ultraviolet light irradiation. The results show that nanocomposites have applicable magnetic and photo catalytic performance.

Electrical and Structural Properties of Bi-Substituted La2Mo2O9 Annealed at Intermediate Temperature

Introduction Oxide-ion conductors find important applications in solid oxide fuel cells and other solid ionic devices. High-temperature polymorph of lanthanum molybdate (La2Mo2O9) has been attracting extensive attention in recent years[1]. The high temperature phase (β phase) of La2Mo2O9, a cubic structure with space group P213, exhibits good ionic conductivity as high as 0.06 S/cm at 1073 K. However, a phase transition from the β phase to low temperature monoclinic α phase takes place around 560-580 °C and leads to a drop in conductivity by nearly two orders of magnitude. Partial substitution of bismuth for lanthanum as La2 – xBixMo2O9 can effectively suppress the α–β phase transition stabilizing β-type structure down to room temperature and restrict the drop in conductivity. Differential scanning calorimetry (DSC) curves of La2-xBixMo2O9 proved the restriction of α–β transition. However, for relatively lower bismuth concentration as x = 0.06, a small endothermic peak sometimes appears around 450–500 °C in DSC traces, which seems to differ from the α-β phase transition [2]. In this work, We report the low temperature stable phase β' from the thermal analyses after various heat treatments. While the newly found β' phase might be related to the dynamic oxygen disorder [3] for the slight difference in XRD patterns between the β and β' phase. Nevertheless, β' phase has been only detected by thermal analysis so far. Then, in the present study, we measured the conductivity and electron diffraction on the annealed samples of La2 – xBixMo2O9 (x = 0.06) to reveal the electric and structural properties of β' phase. Experiment La2-xBixMo2O9 (x = 0.06) sample is prepared by means of conventional sintering method from the mixture of La2O3 (Kishida Chemical, 99.99%), Bi2O3 (Kishida Chemical, 99.9%) and MoO3 (Wako Pure Chemical, 99%) reagents. The calcining and sintering temperatures were selected as500°C and 1000°C, respectively. The sintered sample of β phase was then annealed in a Pt crucible at 460°C to achieve β' phase. Electrical conductivities and structures of the annealed La2 – xBixMo2O9 (x = 0.06) have been investigated by means of a.c. impedance method and transmission electron microscope. Results and Discussion Fig.1 shows the Arrhenius plots of the conductivity measured on annealed La2-xBixMo2O9 (x = 0.06). The conductivity data obtained in the heating and cooling directions are plotted by red and black symbols, respectively. In the lower temperature, both datum disagree each other while they coincide at higher temperature. This indicates that the sample of initially taking β' phase transforms into β phase on heating and the β' phase would supercooled to room temperature. On the other hand, the as-sintered sample shows a concurrence of conductivity curves in both directions. We also found that the as-sintered and annealed have different electron diffraction pattern, while there is only slight difference in XRD patterns. Fig.2 shows the electron diffraction pattern of annealed sample (β' phase) . This pattern indicates that body-centered cubic subcell with a lattice constant of 12.06A accompanied by superlattice reflections. We are now investigating the phase relations between β and β' phase.

Comparison of catalytic activity of bismuth substituted cobalt ferrite nanoparticles synthesized by combustion and co-precipitation method

In this study, cobalt ferrite and bismuth substituted cobalt ferrite (CoFe2−xBixO4x=0, 0.1) nanoparticles were synthesized by two different methods viz combustion and co-precipitation. The nanoparticles were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS), scanning electron microscopy-energy dispersive X-ray analyzer (SEM-EDX) and vibrating sample magnetometer (VSM). The results of powder XRD pattern showed an increase in lattice parameter and decrease in particle size of cobalt ferrite by the substitution of bismuth. Catalytic activity of cobalt ferrite and bismuth substituted cobalt ferrite nanoparticles synthesized by two different methods were compared for the reduction of 4-nitrophenol to 4-aminophenol using NaBH4 as a reducing agent.

PMW-PNN-PZT 세라믹스의 Bismuth 치환에 따른 미세구조 및 압전 특성

In this study, in order to develop the composition ceramics for ultrasonic sensor with high <TEX>$d_{33}*g_{33}$</TEX>, <TEX>$Pb_{1-3x/2}Bix(Mg_{1/2}W_{1/2})_{0.03}(Ni_{1/3}Nb_{2/3})_{0.09}(Zr_{0.5}Ti_{0.5})_{0.88}O_3$</TEX>(PMW-PNN-PZT) system ceramics were prepared using CuO as sintering aids. And then, their microstructure, piezoelectric and dielectric characteristics were systemetically investigated with bismuth substitution. The PMW-PNN-PZT ceramic specimens could be sintered at sintering temperature of <TEX>$940^{\circ}C$</TEX> by adding sintering aids. At x=0.015 specimen, the density, electromechanical coupling factor(<TEX>$k_p$</TEX>), dielectric constant, piezoelectric constant(<TEX>$d_{33}$</TEX>) and piezoelectric figure of merit(<TEX>$d_{33}*g_{33}$</TEX>) indicated the optimal properties of <TEX>$7.90g/cm^3$</TEX>, 0.67, 2,511, 628 pC/N, and <TEX>$17.7pm^2/N$</TEX>, respectively, for duplex ultrasonic sensor application.

High-Temperature Dielectrics in BNT-BT-Based Solid Solution.

Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT)-based ternary solid solutions were investigated for high-temperature capacitor applications. Through a comprehensive investigation of the (1 - x )(0.92Bi0.5Na0.5TiO3-0.08BaTiO3)- x NaNbO3 [(1 - x )(BNT-BT)- x NN, x = 0 -0.45] system, 0.85(BNT-BT)-0.15NN was selected as the parent matrix due to its relatively high permittivity (>1800) and favorable energy-storage density (0.56 J/cm3 at 7 kV/mm). The effect of bismuth substitution on the dielectric properties of the matrix was further characterized. The introduction of bismuth greatly broadened the operational temperature range of 0.85(BNT-BT)-0.15Na1-3yBiyNbO3 ceramics to over 327 °C for a ±15% tolerance. The dc resistivities were of the order of 108 - [Formula: see text] magnitude from room temperature to 300 °C. An activation energy of 1.1-1.2 eV in 200-350 °C was obtained from dc resistivity data, suggesting that the conduction process in this temperature range may be associated with oxygen vacancy migration. Furthermore, the energy-storage properties were largely improved by the addition of bismuth. When the substitution of Bi over Na achieved was up to 7%, the energy-storage density and efficiency reached 0.62 J/cm3 and 88% at 7 kV/mm, respectively. These results confirm that a BNT-BT-based solid solution is a promising candidate for lead-free high-temperature capacitor applications.

Dielectric properties and specific heat of Bi1–x Sm x FeO3 multiferroics

The specific heat and dielectric permittivity of Bi1–xSmxFeO3 (x = 0–0.30) multiferroics have been studied in the temperature range of 300–800 K. A slight substitution of bismuth with samarium is established to cause a considerable shift in the antiferromagnetic phase transition temperature and to an increase in the specific heat over a wide temperature range. Other anomalies typical of phase transitions have been found in the temperature dependences of the specific heat and dielectric permittivity for the compounds with x = 0.10 and 0.15 at T ≈ 735 and 495 K, respectively. The results of the studies of the specific heat have been discussed together with the data of the structural investigations.

Phase transition, dielectric relaxation and piezoelectric properties of bismuth doped La2Ti2O7 ceramics

La2−xBixTi2O7 solid solutions with x ranging from 0.05 to 0.3 were formed through bismuth substitution. Dense and textured ceramics were fabricated by spark plasma sintering. Dielectric spectra indicated an increase in the room-temperature dielectric constant accompanied by a significant drop in the loss tangent as the bismuth content increased. The enhancement in dielectric properties was attributed to the high polarizability of the Bi3+ ion with a lone electron pair. The Curie temperature (Tc) was decreased whereas the d33 value was enhanced. A textured ceramic, Bi0.1La1.9Ti2O7, with Tc~1395±5, and d33~3.6±0.1pC/N was obtained. Complex impedance analysis confirmed the phase transition from orthorhombic Cmc21 to monoclinic P21 in x=0.2 at ~800°C. The observed dielectric relaxation in the temperature range 600–1000°C was ascribed to originate from the Maxwell–Wagner effect.

Influence of bismuth substitution on yttrium orthoferrite thin films preparation by the MOD method

Yttrium orthoferrite thin films with a thickness of about 0.4μm were prepared on glass substrates by using a metal-organic decomposition method. Our studies reveal that it is possible to reduce the crystallization temperature of the yttrium orthoferrite by the substitution of the yttrium ion with bismuth. For the samples BixY1−xFeO3 with x=0.3 and x=0.4, orthorhombic yttrium orthoferrite characteristic peaks in the X-ray diffraction spectra have been detected. The lattice constants of the Bi0.3Y0.7FeO3 film were a=5.905Å, b=7.66Å, c=5.256Å with an average grain size of about 40nm. The magnetization data indicate that the film has in-plane easy axis and weak coercivity which might be explained by a possible secondary garnet phase crystallization. Faraday rotation angle of the sample was measured to be about 0.3°/µm.

Microwave dielectric properties of bismuth-substituted Ba3.75Nd9.5Ti17Al4/3O54 ceramics

The impact of bismuth substitution at neodymium (Nd) site in aluminum-replaced Ba3.75Nd9.5Ti18O54 ceramics on dielectric constant (e r), quality factor (Qf), and temperature coefficient of resonant frequency (τ f ) has been determined (0.05 ≤ x ≤ 0.2). With appropriate quality factor values (Qf > 5000 GHz), the dielectric constant increased from 74.42 to a maximum of 90.8 and the temperature coefficient of resonant frequency was tailored from approximately +20 ppm/°C to the vicinity of 0 ppm/°C. The X-ray diffraction patterns showed a single phase for all compositions, while the scanning electron microscopy and energy-dispersive spectrometer data confirmed XRD results. Factors, such as bulk density, average polarizability, microstructure, and tolerance factor which were caused by the substitution, were taken into consideration to discuss the microwave dielectric properties’ variation. Within substituting limit, a series of controllable microwave dielectric properties (e r = 75.8, Qf = 8994 GHz, τ f = 7.2 ppm/°C; e r = 79.1, Qf = 7282 GHz, τ f = 2.3 ppm/°C; e r = 87.07, Qf = 5548 GHz, τ f = −8.6 ppm/°C) could be obtained when sintered at 1350 °C for 2 h for x = 0.05, 0.1, and 0.15, respectively.

Structural, dielectric and vibrational properties of Ba(1−x)Bix[Ti0.95(Yb0.5Nb0.5)0.05](1−x)FexO3 ceramics (0≤x≤0.2)

Lead-free Ba(1−x)Bix[Ti0.95(Yb0.5Nb0.5)0.05](1−x)FexO3 (0≤x≤0.2) ceramics were prepared using the solid state reaction method. The effect of cationic substitution of Bismuth and iron in A and B sites, respectively, in BaTi0.95(Yb0.5Nb0.5)0.05O3 perovskite on structural and physical properties have been studied using X-ray diffraction, dielectric measurements and Raman spectroscopy techniques. X-ray diffraction analysis revealed that all the samples crystallized at room temperature in a pseudo-cubic Pm3m perovskite structure. Dielectric measurements indicated that the prepared compositions showed a transformation from a classical ferroelectric to relaxor behavior as the rate of substituted x increased. The substitution of Baruim by Bismuth in the A site and Ytterbium/Niobium/Titane by iron in the B site introduced an amelioration in dielectric properties, observed principally in the increasing of the dielectric permittivity maximum and in the decreasing of dielectric loss. Relaxor behavior was also noted to improve, with ΔTm=21K for Ba0.95Bi0.05[Ti0.95(Yb0.5Nb0.5)0.05]0.95Fe0.05O3 at Tm=299K near room temperature. Raman spectra were studied as a function of compositions and temperatures. The results correlated well with dielectric measurements and allowed for a deeper understanding of microstructural properties.

Electric and magnetic properties of Bi substituted cobalt ferrite nanoparticles: Evolution of grain effect

We have prepared Bismuth substituted nano-cobalt ferrite (CoFe2−xBixO4, x=0, 0.05, 0.1, 0.15) by auto combustion technique. The single phase XRD pattern confirmed the successful substitution of the larger cation. Surface morphology from FESEM image indicated the control particle growth (50–160nm) as a result of bismuth substitution. The increased particle size has effectively modified the electrical properties of the system in three major ways: (a) increase in resistivity, (b) evolution of grain relaxation and (c) reduction in dielectric loss and surface conduction. Additionally, magnetic behavior is also affected due to control particle growth. Magnetic hysteresis study at room temperature confirmed the rise in saturation magnetization (MS=74.5–86.5emu/g) and reduction in coercivity (HC=1633–1524Oe).

NontrivialZ2topology in bismuth-based III-V compounds

Realizing topological insulators in commonly used III-V semiconductors is of great importance for their potential application in spintronics and quantum computing. Here we propose a general strategy to realize topological insulators in conventional III-V semiconductors by bismuth substitution and external strain. Based on first-principles calculations, we identify that AlBi (GaBi and InBi) become topological insulators (semimetals) under proper external strain by directly calculating ${\mathbb{Z}}_{2}$ invariants and surface states. Furthermore, we demonstrate that a topological phase transition can be induced by Bi substitution in common III-V semiconductors like GaAs. These proposed topological insulators can be easily integrated into various semiconductor electronic devices and modulated by well-developed modern semiconductor technologies.

Bi_3Fe_5O_12: Dy_2O_3 composite thin film materials for magneto-photonics and magneto-plasmonics

Large Faraday rotations, when achieved simultaneously with low optical losses, lead to obtaining high magneto-optic (MO) figures of merit in bismuth-substituted garnet-type material systems. Demonstrating high MO figures of merit typically requires the synthesis of garnet materials with high bismuth substitution levels (close to 3 Bi atoms per stoichiometric formula unit). In our previous experiments, garnet layers sputtered from a target of nominal stoichiometry Bi3Fe5O12 in pure argon atmosphere showed negligible amounts of specific Faraday rotation after annealing, in contrast with results reported typically for pulsed laser deposition of this material in plasma chemistries containing oxygen. We co-sputter Bi3Fe5O12 together with Dy2O3 in pure argon plasma, and obtain the garnet-type composite thin films on glass substrates possessing a specific Faraday rotation in garnet-Dy2O3 composite films in excess of 14°/µm at 532 nm and a coercive force as low as 100 Oe.

Influence of bismuth on the optical properties of Ge2Sb2Te5 thin films

Chalcogenide alloys in the Ge-Sb-Te system are promising for application in phase-change memory devices. We investigated the influence of bismuth on the optical properties of Ge2Sb2Te5 thin films and established that the bismuth doping in them allows the optical contrast of the thin films to be increased by about 30% at a wavelength of 400 nm. The experimental results are explained in an assumption on the impurity substitution of bismuth for antimony.

Physical properties of new, lead free (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 ceramics

This study reports on the synthesis of polycrystalline samples of (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 with x=0, 0.025, 0.05, 0.075, and 0.1, using the solid-state reaction technique. It investigates the effects of the substitution of sodium and bismuth by barium in the A site and of titanium by iron and niobium in the B site with regard to the free NBT symmetry and dielectric properties were investigated. The crystallographic and dielectric properties were also investigated. The diffractograms showed that all the samples had a single phase character. The increase of ceramic lattice parameters induced an increase in the size of the perovskite lattice. This increase was caused by the increase of the radii of the A and B sites. Room temperature X-ray data revealed that the ceramic structures underwent a gradual distortion with the increase in the composition fraction. Dielectric permittivity was measured in the temperature range of 120–780K with frequencies ranging from 1 to 103KHz. Three anomalies, namely Td, T1 and Tm, were detected and noted to coexist at lower Td and Tm as the rate of substitutions increased. All the samples exhibited a diffuse phase transition and implied better dielectric permittivity maxima values at temperatures approaching room temperature, since the substitution rate values increased more than that of pure NBT. A relaxor behavior with ΔTm=14K and ε'rmax=3876 at 1kHz was observed for (Na0.5Bi0.5)0.9Ba0.1Ti0.9(Fe0.5Nb0.5)0.1O3 ceramic.

Structural, dielectric and magnetic properties of Bi1−xYxFeO3 ([formula omitted][formula omitted]) obtained by acid–base co-precipitation

Bismuth–iron oxides with partial substitution of bismuth by yttrium, referred as (Bi1−xYx)FeO3, were synthesized by simple-low cost acid–base co-precipitation method, which constitutes a difference with the currently used synthetic methods for obtaining BiFeO3-doped compounds (e.g. polymer assisted sol–gel, solid state, microwave, etc.) Samples were characterized by XRD, EDS, SEM, TEM, DSC and FTIR.The influence of yttrium (Y) substitution on magnetization curves of (Bi1−xYx)FeO3 powders were studied at room temperature by VSM. The particle size systematically decreases with the Y percentage. Ferromagnetic curves were obtained at room temperature for Y-percentage lower than 20% with relatively large values of the coercive field, Hc, which increases with Y-substitution, while for 20% yttrium a superparamagnetic behavior is observed.The electrical impedance of compressed disks were investigated also by impedance analysis in the range 1Hz–1MHz and the results were successfully fitted by a simple parallel R–C model. The dc-leakage currents are lower than previously reported for (Bi1−xYx)FeO3 compounds and for most of the doped-BiFeO3 ceramics. As a difference with the influence on the magnetic behavior, the doping with yttrium does not seem to have a large influence on the dielectrical properties. These results suggest that magnetization can be systematically modified by the relatively simple co-precipitation synthesis while keeping invariable the dielectrical properties.

Dielectric and Magnetic Properties of NiFe2-xBixO4 Nanoparticles at Microwave Frequencies Prepared via co-precipitation Method

NiFe2-xBixO4 (x = 0, 0.1, 0.15, 0.20 and 0.25) nanopowders were synthesized via chemical co-precipitation method. The precursor gels were sintered at 973K in air for 2h to obtain the single phase pure nanostructured NiFe2-xBixO4 spinel. The crystal structure and magnetic properties of the substituted spinel series of NiFe2-xBixO4 have been investigated by means x-ray diffraction and vibrating sample magnetometer. The values of the saturation magnetization and the coercive field of NiFe2-xBixO4 nanoparticles were found to decrease with increasing degree of bismuth substitution. The room temperature real and imaginary part of permittivity was measured from 1MHz to 1.8GHz. The real part of permittivity was found to increase with increase of bismuth content. The room temperature electron paramagnetic resonance was studied to investigate the magnetic properties at microwave frequency.

Microstructure and dielectric properties of Ca1–3/2xBixCu3Ti4O12 (x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics

Influence of bismuth substitution on calcium site in CaCu3Ti4O12 has been investigated. Compositions of Ca1-3/2xBixCu3Ti4O12 (x = 0, 0.05, 0.10, 0.15 and 0.20) were fabricated by solid-state sintering method. Crystal structure is remained cubic. X-ray diffraction indicates the presence of secondary phase of CuO in CCTO ceramics. Bismuth doping restrains the formation of CuO phase apparently. The grain size of CaCu3Ti4O12 ceramics was greatly decreased by Bi3+ doping, resulting from the ability of bismuth to inhibit the grain growth. The dielectric and electric properties of CCTO ceramics were found to be influenced by bismuth doping. The fitting results of the complex impedance spectra showed an increase of the resistance of grain and grain boundary by bismuth substitution. Ca0.70Bi0.20Cu3Ti4O12 showed the highest dielectric constant in the low frequency range. A modest composition such as Ca0.85Bi0.10Cu3Ti4O12 expressed the optimized dielectric properties of higher dielectric constant (1.3 × 104) and lower dielectric loss (0.06) than pure CCTO. The low and high temperature dielectric loss spectra demonstrate the interfacial polarization of the initial and secondary oxygen ionization, relating with the grain and grain boundary (the electrode contact for Ca0.70Bi0.20Cu3Ti4O12) respectively.

Enhanced thermoelectric performance in Bi-doped p-type AgSbTe2 compounds

The influence of bismuth (Bi) substitution on the thermoelectric properties of AgSbTe2 compounds was investigated and compared with the undoped AgSbTe2. The addition of Bi dopants not only resulted in a reduction in thermal conductivity but also markedly increased the thermopower in the Ag(Sb1−xBix)Te2 series. Additional phonon scatterings were created by Bi doping and led to a reduction of thermal conductivity. The lattice thermal conductivity is significantly reduced which could be ascribed to enhancement of phonon scattering by dopants with greater atomic weight. In addition, the thermopower was enhanced, which was attributed to the electron-filtering effects caused by the nanoscaled microstructures. Because of the extremely low thermal conductivity (0.48 Wm−1K−1) and moderate power factor of AgBi0.05Sb0.95Te2, a maximum ZT value of (1.04 ± 0.08) was reached at 570 K; yielding an enhancement of greater than 10% compared with an undoped AgSbTe2. this result shows promising thermoelectric properties in the medium temperature range.

Effects of Cation Site Substitutions on the Thermoelectric Performance of Layered SnBi2Te4 utilizing the Triel Elements Ga, In, and Tl

AbstractA thorough study on the thermoelectric potential of the layered compound SnBi2Te4 is presented. Phase range studies on SnBi2Te4, unit cell parameters by powder X‐ray diffraction, and electronic structure calculations (both LDA and GGA functional) were performed. Physical property measurements regarding substitution of tin and bismuth with the triel (Tr = Ga, In, Tl) elements are presented towards the improvement of thermoelectric properties, according to TrxSn1–xBi2Te4 and TrxSnBi2–xTe4. The range of inclusion was generally over 0.01 ≤ x ≤ 0.15 to monitor compound changes as well as phase purity limits. Seebeck coefficient, S, electrical conductivity, σ, and thermal conductivity, κ, were measured, yielding the dimensionless Figure of merit, ZT, data over a temperature range between 300 K and 680 K. Results of partial replacements of tin and bismuth are compared and reported. ZTmax values range from 0.10 to 0.34 depending on the dopant, achieved at temperatures from 355 K to 420 K.