Excess Bismuth Research Articles

Understanding the impact of Bi stoichiometry towards optimised BiFeO3 photocathodes: structure, morphology, defects and ferroelectricity.

BiFeO3 thin films have been widely studied for photoelectrochemical water splitting applications because of its narrow bandgap and good ferroelectricity which can promote the separation of photo-generated charges. Bismuth is well known as a volatile element and excess bismuth is usually added into the precursor to compensate the loss of bismuth during heat treatment, but the amount of excess bismuth required and how excess bismuth will affect PEC performance have not been clearly studied. Herein, self-doped Bi1+x FeO3 thin films are prepared via simple chemical solution deposition method with excess bismuth from 0-30% in the precursor. The loss of bismuth after annealing is confirmed by EDX and XPS. Multiple factors were investigated and it was found that non-stoichiometric Bi resulted in changes of structure, morphology, defects, electronic properties and PEC performance. An enhanced photocurrent is observed in bismuth-rich BiFeO3 films, which can be ascribed to the larger grain size, decreased oxygen vacancies, lattice distortion and supported charge separation. Moreover, the photocathodic performance can be further enhance by ferroelectric poling. Our work indicates that deficient bismuth should be carefully avoided during heat treatment and moreover, a slight excess of Bi is beneficial for PEC performance. Therefore, we offer a simple way to enhance PEC performance of BiFeO3-based ferroelectric materials through careful control of their stoichiometry.

Enhanced photocatalytic activity in BaBi4Ti4O15 with excess Bi2O3

The photocatalytic activity of BaBi4Ti4O15 with excess bismuth oxide (0–10 wt%) and the parametric study of photocatalysis are investigated in this article. BaBi4Ti4O15 with excess bismuth oxide was synthesized via a solid-state route followed by calcination at 950 °C for 4 h. All BaBi4Ti4O15 samples were characterized by X-ray diffractometer, scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and direct optical bandgap. Synthesized BaBi4Ti4O15 with excess bismuth oxide has an orthorhombic perovskite crystal structure with A21am space group. Excess bismuth varies in the concentration of oxygen vacancies, and 8 wt% excess BaBi4Ti4O15 has maximum oxygen vacancy. Excess bismuth also changes direct bandgap; the lowest bandgap is 2.33 eV for 8 wt% excess bismuth. The photocatalytic activity of BaBi4Ti4O15 with excess bismuth oxide (0–10 wt%) showed that 8 wt% excess bismuth has the highest photocatalytic activity. The parametric study of photocatalysis used the initial concentration, volume, and light source intensity as variables. The parametric study suggested that initial concentration, intensity, and volume were correlated with the degradation rate. Indoor dye cleaning in normal room light was also tested for real-life demonstration. BaBi4Ti4O15 was also characterized by an X-ray diffractometer and X-ray photoelectron spectroscopy to investigate the effect of photocatalysis.

Influence of excess bismuth oxide on the structural and dielectric characteristics of textured Bi4Ti3O12 ceramics

Bismuth titanate (Bi4Ti3O12), an Aurivillius family of ferroelectric oxide, has been widely investigated due to its large remnant polarization, high Curie temperature, high dielectric constant and relatively low tangent for the application in information memory storage devices. In this work, polycrystalline bismuth titanate ceramics samples with different amounts of excess Bi2O3 (3 and 5 wt%) were prepared using a low temperature, cost-effective molten salt synthesis method. The structural, microstructural and dielectric properties depend on the addition of excess Bi2O3 and the sintering duration of Bi4Ti3O12 ceramics. Moreover, the X-ray diffraction studies revealed the effect of excess bismuth oxide on the formation of preferential orientation along the c-axis. It is also observed that the orientation factor along the c-axis increases with an increase in the sintering duration for different content of bismuth oxide. The morphological studies revealed the oriented plate-like structure of bismuth titanate ceramics associated with the enhanced growth of grains. It is noticed from the EDAX analysis that the addition of excess bismuth oxide compensated the volatilization of bismuth ions in the crystal lattice of Bi4Ti3O12 ceramics. The dielectric property studies have exhibited a high value of dielectric constant (εr ~ 190), and low tangent loss factor (tanδ ~ 0.08) for the optimum bismuth oxide content of 5 wt% added Bi4Ti3O12 ceramics. Hence, we suggest that these materials could be utilized for the high energy storage capacity of non-volatile memory devices.

Visible Light Photocatalyst and Antibacterial Activity of BFO (Bismuth Ferrite) Nanoparticles from Honey

Visible light-driven photocatalyst BiFeO3 (BFO) nanoparticles were synthesised by the auto-combustion method. The honey was used to fuel the auto combustion method to synthesise the BFO nanoparticles. The structural, optical and morphological activities of the bismuth loaded BFO nanoparticles were characterised by X-ray diffraction (XRD), FTIR, UV, photoluminescence (PL) and SEM analysis, respectively. The bismuth content modifies the lattice parameters of XRD and reduces the bandgap energy. The observed crystallite size varies from 19 to 27 nm and the bandgap region is 2.07 to 2.21 eV. The photo-charge carriers increased upon the BFO nanoparticles and their emission at 587 nm in the visible region of the PL spectrum. The 2% bismuth loaded BFO nanoparticles showed better morphology than 0% and 5% bismuth loaded BFO nanoparticles. The oxidation state of BFO nanoparticles and their binding energies were characterised by X-ray Photoelectron Spectroscopy (XPS) analysis. The methylene blue dye (MB) degradation against 2% BFO nanoparticles showed enhanced catalytic activity (81%) than the remaining samples of BFO nanoparticles. The bacterial activity of BFO nanoparticles was assessed against Gram-positive and Gram-negative bacteria, including S. aureus and E. coli. 2% Excess bismuth BFO nanoparticles exhibit better antibacterial activity. Comparatively, 2% Excess bismuth BFO nanoparticles derived an outstanding crystallinity, charge separation, and reduced bandgap activities. Based on these findings, BFO nanoparticles may be applicable in drug delivery and water remediation applications.

Tuning of high-temperature dielectric properties in the system (Bi0.5Na0.5)TiO3–BaTiO3–CaZrO3

Solid solutions of the (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xCaZrO3 system are regarded as promising dielectrics for high-temperature capacitors as they exhibit a remarkable flat trend of the permittivity over a large temperature range coupled with comparable low dielectric losses. In this work, the composition 0.8(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.2CaZrO3 was chosen in an attempt to optimize especially the high-temperature dielectric properties above 200 °C. In particular, the influence of excess bismuth to account for element losses caused by evaporation, and the effect of manganese as acceptor dopant are reported. Conventional solid-state reaction route was used to synthesize selected compositions. X-ray diffraction was used to confirm a pseudo-cubic perovskite main phase in all examined compositions, although small traces of a zirconia secondary phase were also detected. All samples exhibit an expected flat trend of the relative permittivity with a maximum deviation of the permittivity lower than 15% between −80 °C and 300 °C. The unmodified base composition shows small dielectric loss (<2%) between −55 °C and 265 °C. By using small quantities of manganese doping, the small-loss temperature range was extended (−70 °C and 300 °C). Excess bismuth also affects the temperature-dependent dielectric losses, resulting in a narrowed temperature range, eventually limiting the application possibilities.

Conduction mechanism in excess Bismuth doped Strontium Bismuth Niobate ceramics

Strontium Bismuth Niobate ceramics with excess Bismuth doping (0%wt – 20%wt) were prepared using solid state reaction method. X-ray diffraction studies reveal the decrease in c-axis orientation as bismuth content increases up to 5 ​wt%, beyond that it increases. The dielectric studies were carried out at room temperature as well as at higher temperatures. The ferroelectric properties were found to improve with excess bismuth doping to some extent (5%), indicating compensation for bismuth losses during heat treatment. Temperature dependent dc conductivity studies were done and attempts were made to explain extrinsic and intrinsic conduction mechanisms in Strontium Bismuth Niobate. In low temperature region, the activation energy was found to be very low (0.08eV–0.16eV), which increases (1.07eV–1.14eV) due to introduction of intrinsic defects. A detailed conduction mechanism is presented with excess bismuth doping in Strontium Bismuth Niobate.

Significantly reduced conductivity in strontium titanate-based lead-free ceramics by excess bismuth

Lead-free dielectric ceramics 0.75SrTiO3-0.25BiFeO3 (ST-BF) with an extra amount of bismuth (Bi) are synthesized by the conventional solid-state reaction method. The crystal structures of ST-BF retain pseudo-cubic phase as Bi content increases. The grain size is found to significantly increase from 1.8 to 4.9 µm and then fall to 3.3 µm in the presence of excess Bi, exhibiting a distinct heterogeneous core–shell microstructure. Impedance spectroscopy data indicates that with increasing excess Bi content to 2 mol%, the shell resistivity increases significantly to ∼ 9 MΩ cm with the largest volume fraction of the shell/core area, and both the core and shell activation energies are increased, resulting in reduced dielectric loss of ∼ 0.08 at 1 kHz and high breakdown strength of ∼ 140 kV cm−1. This work provides a potential strategy for further improvement of ST-BF for capacitor applications.

Impact of process conditions on chemical solution deposited BNKT thin film electromechanical properties

Phase pure perovskite (1-x)Bi1/2Na1/2TiO3 – xBi1/2K1/2TiO3 (BNKT) thin films were successfully prepared via an inverse mixing order chemical solution deposition method and the impact of process conditions on film properties were observed. Process conditions evaluated included crystallization temperature and time, ramp rate, pyrolysis temperature, and cation excess. Properties measured included crystal structure, dielectric constant, dielectric loss, piezoelectric response, and ferroelectric response. A few notable trends were observed. A subtle impact on piezoelectric response was observed in films prepared using different ramp rates: 100 C per second films (d33,f = 60 ± 5 pm/V at 1 kHz), 75 °C per second films (d33,f = 55 ± 5 pm/V) and 150 C per second films (d33,f = 50 ± 5 pm/V). Films prepared using a 75 °C per second ramp rate displayed slightly higher dielectric loss (tan δ = 0.09 at 1 kHz) than films prepared using a 100 °C per second ramp rate (tan δ = 0.07 at 1 kHz) or 150 °C per second ramp rate (tan δ = 0.05 at 1 kHz). Pyrolysis temperatures greater than 350 °C are necessary to burn off organics and maximize film dielectric constant. Dielectric constant increased from 450 ± 50 at 1 kHz to 600 ± 50 at 1 kHz by increasing pyrolysis temperature from 300 to 400 °C. Excess cation amounts (for compositional control) were also evaluated and it was found films with higher amounts of Na and K excess compared to bismuth excess displayed an increase in d33,f of about 10 pm/V compared to films prepared with equivalent Bi and Na and K excess amounts.Article highlightsImpact of processing conditions on inverse mixing order chemical solution deposited bismuth based thin films.Dielectric, piezoelectric, and ferroelectric properties of thin film bismuth sodium titanate-bismuth potassium titanate thin films.Developing lead-free piezoelectric actuator materials.

Ice Bath Assisted BiMn2O5(Mullite) Phase Synthesis, Structural and Compositional Analysis under Different Bi Concentration

In this work, ice bath assisted co-precipitation synthesis of nanostructured Bismuth Manganite (BiMn2O5) with varied bismuth concentration and their consequences on the structural properties have rationally been investigated for first time in reports. The novelty of this study is to primarily elucidate the crystalline phase formations and related structural as well as compositional changes while fabricating BiMn2O5 with different amount of Bi content up to 20% to compensate the volatile Bi during annealing process. Powder X-ray diffraction and Rietveld Refinement techniques evidently confirmed the formation of single-phase mullite-type orthorhombic perovskite structure for stoichiometric ratio; while increasing Bi content, a secondary phase sillenite (Bi24Mn2O40) was formed which also gradually increased with increase in bismuth in the precursor solution. Rod and cubic shaped morphologies were commonly observed and size of the particles shows particle size ranging between 45 nm and 120 nm with increase of bismuth content. The mixed morphology is inevitably due to the presence of the secondary phases due to increasing Bi content that are evident from the XRD results. Raman and Optical properties evidently confirmed the structural variation and changes in the band gap respectively owing to the increase in secondary phase evolution with excess bismuth content. X-ray photoelectron spectroscopy (XPS) studies confirmed the increment in Bi content and the coexistence of Mullite and Sillenite phases in the samples.

Эффективная масса, подвижность носителей заряда и решеточная теплопроводность в нанокомпозитных термоэлектриках на основе халькогенидов висмута и сурьмы

In the p-type thermoelectrics based on bismuth chalcogenides and antimony with an excess bismuth, the density of states effective mass m/m0 increases in nanocomposite and nanostructured solid solutions compared with the base material obtained by the direct crystallization method. It is shown that an increase in m/m0 is associated with an increase in the effective scattering parameter reff and amplifying the relaxation time of energy, which is typical for topological insulators. The material parameter beta, proportional to the thermoelectric efficiency of ZT, at temperatures below room increases stronger in nanostructured composition than in a nanocomposite with the inclusions of SiO2 due to the growth of m/m0 and decrease the lattice thermal conductivity κL. At high temperatures in the range of 300-500 to the greatest growth of the parameter beta in the base material associated with higher mobility.

Flux Synthesis of MgNi2Bi4 and Its Structural Relationship to NiBi3.

MgNi2Bi4 was grown from the reaction of magnesium and nickel in excess bismuth flux. It forms as large, malleable crystals with a new structure type in orthorhombic space group Cmcm. The structure contains a building block common to Ni-Bi binary phases-nickel zigzag chains running along one direction and surrounded by bismuth. Magnetic susceptibility and transport measurements indicate that the compound is metallic; this is supported by calculations of density of states. Crystal orbital Hamilton population analyses indicate that Ni-Bi interactions are the strongest bonding interactions in the structure, whereas Bi-Bi bonding between the layers is negligible, making MgNi2Bi4 a potential two-dimensional material.

Effect of bismuth excess on the energy storage performance of 0.5Na0.5Bi0.5TiO3–0.5SrTiO3 ceramics

Lead free 0.5Na0.5Bi0.5TiO3–0.5SrTiO3 ceramics with Bi excess (NB0.5+xT-ST) were prepared by a conventional solid-state reaction method. The effects of bismuth excess on microstructure, dielectric properties and energy storage performances of NB0.5+xT-ST ceramics were investigated systematically. The results show that all ceramics exhibit a perovskite structure with excess Bi doping, the grain size decreased and density enhanced. Typical relaxor ferroelectric P-E hysteresis loops were observed with introduction of Bi2O3. The sample with Bi2O3 excess concentration of 1 mol% exhibits the maximum energy storage density 1.05 J cm−3, which is 2 times higher than that of pure NBT-ST. Meanwhile, the sample displays a high current density of 245.6 A cm−2 and a power density of 6.5 MW cm−3. These results indicate that the Bi2O3 excess improved NB0.5+xT-ST ceramics are useful for potential applications in energy storage ceramic capacitors.

Role of higher valent substituent on the dielectric and optical properties of Sr0.8Bi2.2Nb2O9 ceramics

Abstract The synthesis, structure, optical and dielectric properties of strontium deficient bismuth excess strontium bismuth niobate Sr0.8Bi2.2Nb2O9 (SBNex) ceramics were systematically studied with tungsten and molybdenum as a doping element. The ceramics were prepared with a two-step solid-state method with ∼ 98 % of relative density. The XRD spectrum established that the orthorhombic crystal structure of the Aurivillius oxides was formed and doped with 2.5 at. % of W and Mo resulted in a near phase transition to the tetragonal phase. The energy dispersive X-ray spectra confirmed the formation of the desired compound of strontium deficient bismuth excess SBNex ceramic. The W doped SBNex ceramics exhibited the maximum value of dielectric constant ∼ 270 at the lower frequencies. The dielectric study suggested that the relaxation mechanism be of Debye model with free from any space polarization. The complex modulus plots presented to establish the dielectric relaxation at higher frequency side of the spectra. The band-gap energy (Eg) decreased with Mo and W doping, being 3.00 and 2.85 eV respectively. The enhanced dielectric properties in W and Mo doped SBNex ceramics entitled them for the application to produce high density RAM.

Structure and enhanced electrical properties of high-temperature BiFeO3-PbTiO3-BaZrO3 ceramics with bismuth excess

0.54BiFeO3–0.36PbTiO3–0.1BaZrO3 (BF-PT-BZ) ceramics with various amounts of excess Bi were fabricated by conventional solid-state method and the microstructure and electrical properties were researched to estimate the role of excess Bi on the structure and properties in sintering process. XRD results indicate that tetragonal distortion declined monotonously with the increasing amount of Bi. SEM images reflect that the grain size was enlarged by excess Bi addition. The dielectric, ferroelectric and piezoelectric properties of BF-PT-BZ ceramics were improved effectively. Remnant polarization Pr, piezoelectric coefficient d33 and planar mode electromechanical coupling factor kp of BF-PT-BZ ceramics with 1 mol% Bi excess are 20 μC/cm2, 197 pC/N and 0.448, improved by 20%, 30% and 39%, respectively. The temperature of the maximum dielectric constant Tm of 445 °C for BF-PT-BZ-1 mol% Bi shows tremendous potential for high temperature piezoelectric applications.

Effect of excess Bi on the structure and electrical properties of CaBi2Nb2O9 ultrahigh temperature piezoceramics

CaBi2Nb2O9 + x wt% Bi2O3 (x = 0, 1, 2, 3) ceramics with bismuth layer structure were prepared by solid state reaction route. The effect of excess bismuth on the crystal structure, microstructure and electrical properties of the ceramics was investigated. At all compositions, orthorhombic symmetric bismuth layer structure was formed without secondary phases. Excess bismuth caused more uniform grains. The ceramic with excess Bi2O3 of 1 wt% exhibited optimal electrical properties as follows: piezoelectric constant d33 = 6.4 pC/N, planar electromechanical coupling coefficient kp = 11.0%, dielectric constant $$\varepsilon _{{33}}^{T}/{\varepsilon _0}$$ = 93.5, dielectric loss tanδ = 0.24%, and resistivity ρ = 2.9 × 106 Ω cm (@ 500 °C). This ceramic also possess ultrahigh Curie temperature Tc = 940 °C, indicating its potential application for high temperature sensors and actuators.

Dielectric relaxation study of the ceramic matrix BaBi4Ti4O15:Bi2O3

The dielectric properties of a BaBi4Ti4O15 ceramic were investigated at data temperature range from 340 to 520 °C. The effect of excess bismuth oxide (1–10 wt%) in the ceramics by solid state reaction has been investigated. Rietveld refinement observed increase in the fundamental crystallographic parameter c/a of the 10.8074 up to 10.8900 for BBT, compared to BBT-doped materials. The complex studies of impedance exhibit electrical properties of the material are strongly dependent on temperature. The temperature dependence of the dielectric permittivity showed the presence of a structural phase transition that was observed at near 450 °C. The decrease in value of grain and grain boundary resistance with increasing temperature suggests the existence of an increase of the conductivity. The nature of variation of DC conductivity with temperature confirms the Arrhenius behavior of the material. The DC electrical and thermal conductivity of grain and grain boundary have been assessed.

Phase pure epitaxial growth of BiFeO3 films: An effect of oxygen partial pressure

We report the growth of bismuth ferrite, BiFeO3 (BFO), thin films by varying oxygen partial pressure (230, 100 and 10mTorr) in pulsed laser deposition system using 10% bismuth excess BFO target on SrTiO3 (001) [STO] substrates at 700°C each for 15min duration. X-ray diffraction shows the presence of an impurity phase along with BFO peaks for 230mTorr film, whereas oriented BFO film is observed for 100mTorr film with a small impurity phase. Importantly, epitaxial growth of BFO is observed without any impurity phase and with sufficiently increased strain for the 10mTorr film, confirmed by the reciprocal space mapping of (002) and (103) reflections. UV-Raman measurements have been performed on as grown films and the 10mTorr BFO film after annealing up to 500°C to check its thermal stability. Atomic force microscopic (AFM) study reveals that the 10mTorr BFO film shows a lower roughness as compared to 100mTorr and 230mTorr films. Fast Fourier Transform (FFT) analysis in AFM shows a fourfold symmetric structure suggesting the presence of both modes of pattern-orientation in 230mTorr BFO film whereas an elongated bright spot along the y-direction in the FFT of 10mTorr BFO film suggests the growth tendency to be along the y-direction.

Chemical pressure induced change in multiferroicity of Bi1+2xGd2x/2Fe1−2xO3 bulk ceramics

We have optimized Gd ion substitution in BiFeO3 (BFO) and observed prominently change in structural, electrical and magnetic behavior of Bi1+2xGd2x/2Fe1−2xO3 ceramics synthesized through slow step sintering schedule. It is observed that with the increase in concentration of Gd (x=0.1), original structure of BFO is transformed from rhombohedral R3c space group to orthorhombic Pn21a space group. Surprisingly, unit cell volume is drastically contracted (35% for x=0.2) and the sintered specimen showed enhanced room temperature ferromagnetic behavior although the original BFO is normally G-type antiferromagnetic in nature at 643K. It is expected that intrinsic chemical pressure within the bulk body built by the substitution of Gd in presence of excess bismuth greatly supported through unidirectional movement of electrical dipole moment with in each individual domain as a result of which suppression of leakage current with enhanced dielectric and ferroelectric hysteresis is observed.

Effects of excess Bi on structure and electrical properties of BiFeO3 thin films deposited on indium tin oxide substrate using sol–gel method

As a kind of potential unleaded multiferroic material, BiFeO3 (BFO) is expected to be used instead of Pb(Zr,Ti)O3 in high density ferroelectric random access memories. Bi1+xFeO3 (x = 0, 5, 10, 15 and 30 %) thin films deposited on indium tin oxide/glass substrate were successfully fabricated using sol–gel method, spin coating and layer by layer technique. The XRD and SEM analysis indicated that the orientation of BFO thin films is sensitive to the content of excess bismuth. Both sense surface and suppression of impurity phases were realized in the BFOx=10% thin films. Adding appropriately excess Bi can cover the volatilization of Bi2O3 during the thermal treatment. Leakage current density and P–E hysteresis loop demonstrate that x = 10 % is the best excess Bi content. BFOx=10% thin films has a minimum current density of 7.8 × 10−9A/cm2 at applied electric field of 600 kV/cm, a maximum remnant polarization 71.18 μC/cm2 with a coercive field of 412.52 kV/cm at measured electric field value of 1213 kV/cm, and a largest dielectric constant 208 with a relatively lower dielectric loss of 0.042 at applied frequency of 105 Hz, of which the current conduction mechanisms are Ohmic conduction and grain boundary limited conduction.

Synthesis, Characteristics, and Material Properties Dataset of Bi:DyIG‐Oxide Garnet‐Type Nanocomposites

The fabrication, annealing crystallization processes, and material properties of (Bi,Dy)3(Fe,Ga)5O12:Bi2O3 nanocomposites are investigated and summarized. The stoichiometry of these nanocomposites is optimized for magnetooptic applications using the approach of stoichiometry adjustment (implemented by means of varying RF power densities applied to the sputtering targets used to prepare the nanocomposite thin films). The crystallization processes for all developed batches of as‐deposited films are carried out by annealing runs at different temperatures and process durations. This paper describes the methodologies used to optimize the compositions (by calculating the volumetric fractions of excess bismuth oxide to be mixed with the garnet‐stoichiometry species during cosputtering processes) and to obtain the optical and magnetooptical properties data and presents the materials properties summary of garnet‐bismuth oxide thin film composites as well.