Sillenite Structure Research Articles

Enhanced electrochemical oxygen generation from sillenite phase of bismuth iron oxide (Bi24Fe2O39) ultrafine particles stabilised at room temperature

Recently, lot of research is going on in development of clean energy-based technology to address the issue of exponentially increasing energy demands. Electrochemical water splitting is a clean and efficient process for generation of H2 and O2. Water electrolysis produces hydrogen and oxygen on cathode and anode respectively as separate half-cell reactions is one of the most important clean alternative processes. This work reports synthesis of Bi24Fe2O39 ultrafine crystalline nanoparticles via facile room temperature chemical method for the first time. Bi24Fe2O39 shows a spherical morphology with an average size of 8 nm. As obtained Bi24Fe2O39 acts as an electrocatalyst for electrochemical oxygen evolution reaction (OER). Electrochemical oxygen generation studies confirm the overpotential of 420 mV in 1 M KOH solution at a current density of 10 mA/cm2. Tafel slope and EIS studies give further insight of oxygen generation process. The results show that Bi24Fe2O39 exhibits low Tafel slope of 63 mV dec−1 and a very low charge transfer resistance of ∼10 Ω. This study paves a new way for future research into bismuth based sillenite structure for various energy related applications.

Discovery of Unconventional Proton‐Conducting Inorganic Solids via Defect‐Chemistry‐Trained, Interpretable Machine Learning

AbstractHigh‐throughput computational screening and machine learning hold significant potential for exploring diverse chemical compositions and discovering novel inorganic solids. However, the complexity of point defects, which occur in all inorganic solids and are often crucial to their functionality and synthesizability, presents significant challenges. Here, this study presents a defect‐chemistry‐trained, interpretable machine learning approach, designed to accelerate the exploration and discovery of unconventional proton‐conducting inorganic solid electrolytes. By considering dopant dissolution and hydration reactions, the machine learning models provide quantitative predictions and physical interpretations for synthesizable host–dopant combinations with hydration capabilities across various structures. Utilizing these insights, two unconventional proton conductors, Pb‐doped Bi12SiO20 sillenite and eulytite‐type Sr‐doped Bi4Ge3O12, are discovered in the first two synthesis trials. Notably, the Pb‐doped Bi12SiO20 represents an unprecedented class of proton‐conducting electrolyte composed solely of groups 14 and 15 cations and featuring a sillenite structure. It exhibits unique and fast 3D proton conduction along a loosely bonded BiO5 network. This study demonstrates an efficient approach for exploring novel inorganic materials.

Microstructures, Magnetic Properties and Specific Absorption Rate of Polymer-Modified Bismuth Ferrite Nanoparticles

Bismuth ferrite nanoparticles were successfully synthesized by the co-precipitation method and modified by polyethylene glycol (PEG) 4000. X-ray diffraction patterns showed a sillenite structure of bismuth ferrite (Bi25FeO40) with a crystallite size of 35.0 nm and the new phase appeared after surface modification. The new phase was Bi2Fe4O9. Crystallite size increased after surface modification of nanoparticles with PEG. The highest increase of crystallite size after surface modification with PEG was 40.1 nm. Transmission electron microscopy images showed that samples before and after surface modification were polycrystalline and still agglomerated. Spectra of Fourier transform infrared showed the presence of C-O stretching at 1080 cm-1 and C-H bending vibration at 1342 cm-1 in the bismuth ferrite/PEG sample, which did not appear in bismuth ferrite sample. The magnetic measurement indicated the weak ferromagnetic properties of the samples. Saturation magnetization did not appear after a maximum external magnetic field (15 kOe) was applied. The maximum magnetization of nanoparticles was 0.5 emu/g and tended to decrease to 0.2 emu/g after surface modification with PEG. Optical properties analysis showed a shift in the maximum absorption peak of bismuth ferrite nanoparticles towards a lower wavelength (blue shift) after surface modification of the nanoparticles. The specific absorption rate (SAR) value of nanoparticles increased by increasing an alternating magnetic field (AMF) strength. The SAR values of bismuth ferrite nanoparticles were 48.8, 61.4, and 84.4 mW/g and decreased to 32.0, 45.2, and 83.3 mW/g after surface modification at the AMF strength of 150, 200, and 250 Oe, respectively.

Preparation and characterization of a novel luminescence nano-sillenite (Bi12SiO20) glass ceramic within Bi2O3–ZnO–SiO2 system

Bismuth silicate with sillenite structure (Bi12SiO20) nanophase was prepared via melt–quenching technique in the Bi2O3–ZnO–SiO2 glass system. The effect of replacement ZnO by Bi2O3 was studied. Their thermal behavior showed the change of glass transition temperature (Tg) from 577 °C in the Bi2O3-free glass to 438 °C in ZnO-free glass. In addition, the crystallization temperatures were not only changed from two to one peak, but also decreased from 927 to 476 °C in the same order. According to the heat treatment regimes, willemite, sillenite, tetragonal Bi2O3, cubic Bi2O3 and traces of ZnO were crystallized with different ratios depending on the change in composition and temperature. Sillenite was enhanced with increase heat treatment temperature and/or Bi2O3 additions. Heat treatment at 650 °C/10 h revealed the best regime, where higher degree of crystallization was achieved. The microstructure at 700 ℃/30 min showed nano-scale oriented parallel rod crystals with hexagonal making at their end, whereas clusters of irregular nano-size crystals was appeared at 650 °C/10 h. Transmission spectra of the glasses in UV–Vis–midIR region were increased with Bi2O3 addition reaching 74% in 100B. Photoluminescence properties of both glasses and their corresponding glass–ceramics showed luminescence nature since the blue and green colors were clearly appeared. Calculation of optical bandgap (Eopt) revealed 3.2–2.19 eV with increasing Bi2O3; these values are located in the semiconducting range. The prepared samples can be utilized in electro-optical instruments, also the high transmission in mid-IR nominate it for IR transmitting windows.

Simple Low Temperature Technique to Synthesize Sillenite Bismuth Ferrite with Promising Photocatalytic Performance

Sillenite-type members of the bismuth ferrite family have demonstrated outstanding potential as novel photocatalysts in environmental remediation such as organic pollutant degradation. This investigation has developed a low temperature one-step hydrothermal technique to fabricate sillenite bismuth ferrite Bi25FeO40 (S-BFO) via co-substitution of 10% Gd and 10% Cr in Bi and Fe sites of BiFeO3, respectively, by tuning hydrothermal reaction temperatures. Rietveld refined X-ray diffraction patterns of the as-synthesized powder materials revealed the formation of S-BFO at a reaction temperature of 120–160 °C. A further increase in the reaction temperature destroyed the desired sillenite structure. With the increase in the reaction temperature from 120 to 160 °C, the morphology of S-BFO gradually changed from irregular shape to spherical powder nanomaterials. The high-resolution TEM imaging demonstrated the polycrystalline nature of the S-BFO(160) nanopowders synthesized at 160 °C. The as-synthesized samples exhibited considerably high absorbance in the visible region of the solar spectrum, with the lowest band gap of 1.76 eV for the sample S-BFO(160). Interestingly, S-BFO(160) exhibited the highest photocatalytic performance under solar irradiation, toward the degradation of rhodamine B and methylene blue dyes owing to homogeneous phase distribution, regular powder-like morphology, lowest band gap, and quenching of electron–hole pair recombination. The photodegradation of a colorless organic pollutant (ciprofloxacin) was also examined to ensure that the degradation is photocatalytic and not dye-sensitized. In summary, Gd and Cr co-doping have proven to be a compelling energy-saving and low-cost approach for the formulation of sillenite-phase bismuth ferrite with promising photocatalytic activity.

Role of crystal structure and electrical polarization of an electrocatalyst in enhancing oxygen evolution performance: Bi-Fe-O system as a case study

This work aims to give an insight into the influence of crystal structure (for a system containing same elements but crystallizing in different structures) and the effect of electrical polarization on these oxides on the performance of oxygen evolution reaction (OER). We have tried to highlight this influence by taking the Bi-Fe-O system for the study. Herein, we have synthesized three structures of the Bi-Fe-O system viz. BiFeO3 (perovskite structure), Bi2Fe4O9 (mullite structure), and Bi25FeO40 (sillenite structure) as an example to establish the relation. These oxides were characterized by Rietveld refinement for structure and scanning electron microscopy (SEM) for morphology. Their optical and magnetic properties were also investigated. Systematic studies were carried out with both as-synthesized and electrically polarized oxides for their performance towards OER. We observed that the order for OER activity (using non-polarized catalyst) of the three stable structures synthesized was Bi2Fe4O9 > BiFeO3> Bi25FeO40, which was attributed to the presence of Fe(oct)-O-Fe(td) linkages in Bi2Fe4O9. While the current density of Bi2Fe4O9 and BiFeO3 remained unchanged after poling, that of Bi25FeO40 increased by four-fold. From the study, we have demonstrated that proper choice of the crystal structure and utilization of electrical polarization can be effective strategies to manipulate the surfaces of an electrocatalytic material.

(Bi13Co11)Co2O40–Co3O4 nanocomposites: Approach to different fuels in sol-gel combustion synthesis using the Box-Behnken design

The sol-gel combustion method was applied using three types of fuels (urea, glycine, and ethylene glycol) to synthetize Co sillenite. A Co sillenite - Co3O4 nanocomposite was obtained as result of the synthesis. The effects of initial pH, fuel type, and amount of fuel on the relative mass concentration of Co Sillenite phase present in the nanocomposite, obtained by Rietveld refinement of XRD data, were evaluated by the Box-Behnken design of experiments. Statistical analysis allowed the quantification of each synthesis parameter and the choice of the samples with higher relative mass concentration of Co Sillenite for each type of fuel. The selected samples were analyzed by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDX), x-ray fluorescence (XRF) and dielectric open-ended coaxial probe techniques. Rietveld refinements showed that Co sillenite and Co3O4 have cubic structure, and Co sillenite structure belongs to I23 space group. The Co sillenite has crystallite sizes of 43.6 nm (urea), 40.3 nm (glycine) and 44.1 nm (ethylene glycol). The FESEM images displayed a significant change in samples morphology, presenting sphere, flakes and flowers-like shapes. The samples purity was confirmed by the presence of Bi, Co and O elements, identified through EDX. Functional groups and vibrational modes of Co sillenites (Bi–O, Co–O) were identified by FT-IR technique and Raman spectroscopy. Dielectric properties measurements displayed accordance with structural characterizations of each sample. Low losses could also be achieved above 4.5 GHz, leading to a composite suitable for highly efficient microwave systems.

Rational design of n-Bi12TiO20@p-BiOI core–shell heterojunction for boosting photocatalytic NO removal

Bismuth titanate (Bi12TiO20) with unique sillenite structure has been shown to be an excellent photocatalyst for environmental remediation. However, the narrow light-responsive range and rapid recombination of photoinduced electrons-holes limit the photocatalytic performance of Bi12TiO20. To overcome the limitations, a practical and feasibleway is to fabricate heterojunctions by combining Bi12TiO20 with suitable photocatalysts. Here, using a facile chemical precipitation method, a novel and hierarchical core–shell structure of n-Bi12TiO20@p-BiOI (BTO@BiOI) heterojunction was rationally designed and synthesized by loading BiOI nanosheets on BTO nanofibers. The constructed BTO@BiOI composites exhibited significant charge transfer ability due to the synergistic effects of the built-in electric field between BTO and BiOI as well as close interfacial contacts. In addition, the narrow bandgapcharacteristics of the BiOI led to wide light absorption ranges. Therefore, the BTO@BiOI heterojunction exhibited an improved photocatalytic performance under visible light irradiation. The NO removal efficiency of optimal BTO@BiOI was 45.7%, which was significantly higher compared tothat of pure BTO (3.6%) or BiOI (23.1%). Moreover, the cycling experiment revealed that BTO@BiOI composite has a good stability and reusability. The possible mechanism of photocatalytic NO oxidation over BTO@BiOI was investigated in detail.

Optical, electrical, and catalytic (photo-and sono-) properties of indium doped γ-Bi2O3 with Sillenite structure

The exotic structure and properties exhibited by the metastable solids are exemplified adequately in the materials chemistry area. In this report, metastable γ-Bi2O3 has been stabilized without adding any impurity by the auto-combustion method and compared with the changes in structure and optical property brought out by the inclusion of In3+ ions. Compositions doped with indium (7 and 10 mol% in place of bismuth) resulted in stoichiometric Sillenite-type structures as revealed by their powder X-ray diffraction patterns, FTIR, and Raman spectral measurements. The pale yellow γ-Bi2O3 acquired pale brown coloration on indium inclusion, and the intensities varied with varying indium content. Optical bandgap reduction from 2.63 (pure γ-Bi2O3) to 2.41 eV occurred when 10 mol% of indium was doped in place of bismuth. The formation of non-stoichiometric Sillenite structures was noticed in samples with higher indium concentrations (up to 50 mol%). The non-stoichiometric samples displayed intense brown color and showed a drastic reduction in the optical bandgap, reaching values as low as 1.57 eV (50 mol% indium doped sample). From XPS analysis and red-ox titrations, nearly 5% of oxygen excess was estimated for the non-stoichiometric samples doped with indium. The BET surface area of indium doped non-stoichiometric Sillenites (126 m2/g) was higher than indium doped stoichiometric Sillenites (74 m2/g). The oxygen ion conductivity studies of pure γ-Bi2O3 and indium doped non-stoichiometric Sillenites revealed a marginal rise in conductivity with indium inclusion.

Synthesis and Characterization of Bi13B0.48V0.49-xPxO21.45 and Efficient Catalyst for the Synthesis of 2,3-dihydroquinazolin-4(1H)-ones Derivatives Synthesis

A new compound has been found in the system Bi13B0.48V0.49-x PxO21.45 (with 0≤x≤0.34), were prepared by the direct solid-state reaction of Bi2O3, (NH4)2HPO4, V2O5, and B2O3. This material melts congruently and it crystallize with the sillenite structure (space group I23) and form a solid solution with the cubic lattice parameter increasing from with a = 10.1568 Å to 10.1436 Å with increasing of P2O5 molar. Consequently, the new composites belong to g-variety of solid state. The samples have been characterized by Fourier transform infrared spectroscopy (FT-IR), diffraction XRD and scanning electron microscopy (SEM) coupled to the EDX. On the other hand, the valorization of the prepared composites was performed by using them as heterogeneous catalyst in the 2,3-dihydroquinazolin-4(1H)-ones derivatives synthesis. The catalyst is stable (as a bench top catalyst) and reusable. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Synthesis and properties of novel inorganic green chromophore based on Bi24Al2-xMnxO39

Bi24Al2-xMnxO39 (0 ≤ x ≤ 0.8) solid solution with sillenite structure is successfully prepared by conventional solid state method at 750 °C. By the substitution of Mn to Al, the color of the compound is tuned from pale yellow (x = 0) to yellowish green (x = 0.5) and intense green (x = 0.8). The space group of the as-synthesized samples is confirmed to be I23 by X-ray powder diffraction (XRD). The oxidation state of Mn is proved to be +4 by X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). Based on UV–Vis absorbance spectra, Mn4+ ions in tetrahedral site and its d-d transition are responsible for the green color. The color properties of the as-synthesized samples are maintained after acid resistance test.

Elastic properties of single crystal Bi12SiO20 as a function of pressure and temperature and acoustic attenuation effects in Bi12MO20 (M = Si, Ge and Ti)

A comprehensive study of sillenite Bi12SiO20 single-crystal properties, including elastic stiffness and piezoelectric coefficients, dielectric permittivity, thermal expansion and molar heat capacity, is presented. Brillouin-interferometry measurements (up to 27 GPa), which were performed at high pressures for the first time, and ab initio calculations based on density functional theory (up to 50 GPa) show the stability of the sillenite structure in the investigated pressure range, in agreement with previous studies. Elastic stiffness coefficients c11 and c12 are found to increase continuously with pressure while c44 increases slightly for lower pressures and remains nearly constant above 15 GPa. Heat-capacity measurements were performed with a quasi-adiabatic calorimeter employing the relaxation method between 2 K and 395 K. No phase transition could be observed in this temperature interval. Standard molar entropy, enthalpy change and Debye temperature are extracted from the data. The results are found to be roughly half of the previous values reported in the literature. The discrepancy is attributed to the overestimation of the Debye temperature which was extracted from high-temperature data. Additionally, Debye temperatures obtained from mean sound velocities derived by Voigt-Reuss averaging are in agreement with our heat-capacity results. Finally, a complete set of electromechanical coefficients was deduced from the application of resonant ultrasound spectroscopy between 103 K and 733 K. No discontinuities in the temperature dependence of the coefficients are observed. High-temperature (up to 1100 K) resonant ultrasound spectra recorded for Bi12MO20 crystals revealed strong and reversible acoustic dissipation effects at 870 K, 960 K and 550 K for M = Si, Ge and Ti, respectively. Resonances with small contributions from the elastic shear stiffness c44 and the piezoelectric stress coefficient e123 are almost unaffected by this dissipation.

Structural, Electrical and Morphological Properties of Materials Type Sillenite Phase Bi12TiO20

This work reports the investigation of the ternary system Bi2O3–TiO2–MgO. Some compositions have been synthesized by solid state reaction at 800 °C and characterized by powder X-ray diffraction. The doping of (α-Bi2O3) allowed us to stabilize three compositions isotype of sillenite structure phase with formulas Bi0.9 Ti0.1 O1.55, Bi0,9 Ti0,05Mg0,05 O1,5, and Bi0.8 Mg0.1 Ti0.1 O1.5. The structural resolution of the synthesized materials was performed using Rietveld method by means of FullProf program. It crystallizes in the cubic system. The space group I23 and lattice parameter a = 10.1723(2) A. The morphological proprieties of the synthesized compositions have been investigated by means of scanning electron microscopy (SEM). Sintered samples showed a dense and uniform microstructure. The density of sintered samples obtained is nearly 92% of the theoretical density. Various impedance model including capacity and Warburg impedances have been used to interpret the Nyquist representations of electrical analyses. The highest conductivity is observed for Bi0.9 Ti0.1 O1.55 (σ = 1.39E−07 at 600 °C).

Synthesis of Stable Bismuth Silicate with Sillenite Structure in the Na2O–Bi2O3–SiO2 System

A combined method for synthesizing a highly dispersed (0.8–2.5 μm) hydrophobic Na2O–Bi2O3–SiO2 powder (NBS powder) based on solutions of sodium methyl siliconate and bismuth nitrate is studied. The powder is synthesized at a reduced temperature (100°C). The microstructure and the phase composition of the resulting compounds in the Na2O–Bi2O3–SiO2 system at different processing temperatures are investigated. The structural phase transformations in the mineral phases of NBS powder are revealed in the temperature range of 100–500°C. The metastable bismuth silicate Bi2SiO5 at 400°C is transformed into stable sillenite with composition Bi12SiO20 having a cubic crystal structure (a = 10.1050 A). The synthesized NBS powder can be used as a filler to fabricate highly effective constructional radiation-shielding polymer composites with tailored properties.

Formation of nanocrystalline BiFeO3 under hydrothermal conditions

The formation of bismuth orthoferrite under hydrothermal conditions at temperature 160, 180, or 200°С and pressure 100 MPa in aqueous solution of potassium hydroxide has been studied. The determined composition and structure of polycrystalline phase with sillenite structure have evidenced its formation at the interface of the crystallites of amorphous iron oxide. It has been shown that the formation of polycrystalline round-shaped BiFeO3 particles with size about 20 μm occurs via aggregation of perovskite-type phase crystallites (38–70 nm). Pycnometric density of BiFeO3 and the amorphous phase has been determined, and Mossbauer spectra reflecting the state of iron in the phases coexisting during the formation of BiFeO3 have been analyzed.

Synthesis and optical characterization of In3+-stabilized γ-Bi2O3 sillenite semiconductor with cation deficiency

Bi3+-containing semiconductors usually show rich optical and electronic properties due to the hybridization between 6s and 6p electronic components together with the lone pair in Bi3+ ions. In this work, an In3+-stabilized γ-Bi2O3 sillenite structure, Bi24InO37.5 (Bi12In0.5O18.75), was prepared through the facile sol-gel method. The samples developed into ball-like nanoparticles with size of 200–300nm. The Rietveld structure refinement was performed. Bi24InO37.5 belongs to cubic sillenite-structure of metastable cubic γ-Bi2O3 (space group I23), a well-known group of non-centrosymmetric crystal. The morphological characteristics were tested by SEM, TEM, EDS and Brunauer–Emmett–Teller (BET) measurements. The optical absorption, band gap energy and electronic structures were discussed. In contrast to the reference Bi2O3, Bi24InO37.5 shows a narrower band energy of 2.48eV. Meanwhile, it has a self-activated emission with a low luminescence quenching.

Structure peculiarities and point defects in new sillenite-type (Bi,Sm)24V2O40 crystals

Single-crystal (Bi,Sm)24V2O40 solid solutions with sillenite structure, grown by the hydrothermal method for the first time, have been studied using single-crystal X-ray diffraction, synchrotron radiation, and infrared spectroscopy. The real composition has been refined. The presence of Sm3+ and Bi3+ ions in one crystallographic site was determined by single-crystal X-ray diffraction and confirmed by the analysis of infrared spectra and calculation of the degree of distortion of the real [BiO5] polyhedron.

Synthesis of Bi25FeO39 by molten salts method and its mössbauer spectrum

A sample of Bi25FeO39 was synthesized by the molten salts method in 2h at 750°C with KCl-KBr as reaction media. The sample was characterized with X-ray powder diffraction and Mössbauer spectroscopy. The Rietveld refinement of the X-ray diffraction confirms that a sillenite type structure with a cell parameter a=10.190(4)Å was achieved, with only small traces of Bi2O3. In order to get a Mössbauer spectrum with a good signal to noise ratio, the synthesis was made using 95% enriched α–57Fe2O3. To our knowledge, this is the first time that a Mössbauer spectrum for the Bi25FeO39 has been recorded. The nonappearance of a magnetic sextet confirms its paramagnetic behavior. The measured Mössbauer parameters (IS=0.20±0.004mm/s and QS=0.2±0.07mm/s) correspond to Fe+3 in very symmetric surroundings, and rule out some interpretations given to the doublet observed in some Mössbauer spectra of BiFeO3.

Composition‐Controlled Synthesis of Bismuth Vanadate Photocatalysts via a Facile Electrochemical Method

Bismuth vanadate compounds including BiVO4, Bi25VO40, and the composite Bi25VO40/Bi7V11O9 with photocatalytic properties were firstly synthesized via a facile electrochemical strategy. The amount of NaOH in the electrolyte and electric currents were discovered to be crucial variables to the composition, morphology, and crystallinity of the products. Monoclinic phase BiVO4 and Bi25VO40 with sillenite structure can be obtained at 2 A with NaOH concentration of 0–10−4 and 0.1–0.4M, respectively. The acquirement of Bi25VO40/Bi7V11O9 can be achieved with electric current 3–5 A in an electrolyte containing 0.4M NaOH. All the electrosynthesized samples exhibit good visible‐light‐driven photocatalytic activity in the degradation of rhodamine B, much higher than that of the commercial TiO2 (P25).

Enhanced reactivity of peroxo-modified surface of titanium dioxide nanoparticles used to synthesize ultrafine bismuth titanate powders at lower temperatures

Bismuth titanate with sillenite structure (Bi12TiO20) was prepared at lower temperatures and shorter times using a modified oxidant peroxide method (OPM). Bi12TiO20 was synthesized utilizing commercial Bi2O3 and reactive titanium dioxide nanoparticles having peroxo-modified surfaces. Rather than depending on particle size, the reaction mechanism is related to the highly exothermic decomposition of peroxo groups, regardless the titanium source used, which locally releases a large amount of energy that can accelerate the reaction, similar to self-propagating high temperature routes (SHS).