Bismuth Layer Research Articles

Phase transitions and ferroelectricity of perovskite layered Sr2Nb2O7 ceramics

Spontaneous polarization (Ps) is the fundamental for ferroelectrics. Compared with the relative explicit origin of Ps of perovskite ferroelectrics and bismuth layer structured ferroelectrics, that of the perovskite layer structured ferroelectrics (PLSFs) is still unclear and controversial due to their unique layer structures. Sr2Nb2O7 compound with a high Curie temperature of 1342 °C is a typical representative in the family of PLSFs. Here, we report our investigations about the phase transitions and the mechanism of ferroelectricity of Sr2Nb2O7 ceramics from the viewpoint of layered crystal structure experimentally and theoretically. Sr2Nb2O7 has two phase transitions at about 215 °C and 1340 °C. Selected area electron diffraction (SAED) images show superlattice along the [001] zone axis related to an incommensurate modulation and confirm it's incommensurate-commensurate phase transition at around 215 °C. The latter on at 1340 °C corresponds to the paraelectric-ferroelectric phase transition which is originated from oxygen octahedral rotation along c-axis, named a0b0c+ in Glazer's notation. Phonon spectra shows the origin of Ps for Sr2Nb2O7 is from mainly the oxygen octahedral rotations and partially the displacement of Sr2+ ions. This study not only demonstrates the rotation of oxygen octahedron is the domination that affects ferroelectric polarization but also opens up a new direction to design high ferroelectric and piezoelectric PLSF ceramics.

Effects of lanthanide ions on the structure and electrical properties of Aurivillius Bi3TiNbO9 high temperature piezoelectric ceramics

Aurivillius Bi3TiNbO9 has a very high Curie temperature (Tc), but the piezoelectric coefficient (d33) is very low, and the influence of ions with different radii on its performance is not clear. High temperature piezoelectric ceramics Bi2.99(Li0.5Ln0.5)0.01TiNbO9 (BTNO-1LiLn, Ln = La, Nd, Gd, and Er) were prepared by solid state reaction sintering, and its microstructure, piezoelectric properties and electrical conductivity were systematically studied. The Tc of BTNO-1LiLn increases with the decrease of Ln3+ ions radii. BTNO-1LiEr obtains the highest d33 of 10.6 pC/N. Considering the cation disorder of A-site and bismuth layer of calcium titanium layer in Aurivilius structure, the crystal structures of BTNO-1LiLa with special occupation and BTNO-1LiEr with the best performance are refined, and the source of spontaneous polarization (Ps) is analyzed. It is proved that different occupation will have different effects on the high temperature piezoelectric properties and fatigue cycle properties of BTNO based ceramics. Finally, the band structure of BTNO pure ceramic based on the first principle is calculated. By comparing the activation energy and band gap width, it is indicated that (Li0.5Ln0.5)2+ ions entering BTNO will form impurity energy levels and form p-type semiconductors. This study provides a theoretical basis for better performance of BTNO based high temperature piezoelectric ceramics.

Bismuth-based broadband metamaterial absorber

A numerical simulation of a metamaterial broadband absorber is performed using the finite-difference time-domain method. The absorber adopts a four-layer structure with titanium dioxide (TiO2) rectangular pairs, a bismuth (Bi) layer, a silicon dioxide (SiO2) layer, and a titanium nitride (TiN) layer from top to bottom, respectively, and the TiO2 rectangular pairs are periodically and symmetrically arranged in a rectangular array. The optimization results show that the average absorption of the designed absorber is 97.6% in the wavelength range of 500 to 3500 nm and the average absorption can reach 99% in the wavelength range of 811 to 3162 nm (2351 nm). The coupling of local surface plasmon resonance and propagating plasmon resonance and the good absorption and broadband absorption properties exhibited by metallic Bi were further found by analyzing the distribution of electromagnetic fields. The designed absorber has polarization and temperature-insensitive properties and a simple structure and is easily fabricated.

Ca2+ doping effects on the structural and electrical properties of Na0.5Bi4.5Ti4O15 piezoceramics

Bismuth layer structured Na0.5Bi4.5Ti4O15 (NBT) ferroelectric is one of the most promising materials for potential applications at high temperature. However, it is challenged to achieve a balance between high Curie temperature piezoelectric coefficient and excellent thermal stability for NBT piezoceramics. Here, through chemical modification at the A site of NBT with Ca2+, novel (Na0.5Bi0.5)1-xCaxBi4Ti4O15 piezoceramics with excellent properties fabricated by solid state reaction were studied. After doping of Ca2+, the Curie temperature TC increased from 648 °C to 662 °C while the piezoelectric coefficient d33 increased from 14 pC/N to 22 pC/N which can be attributed to the intrinsic contribution of TiO6 octahedral lattice distortion (tilting and rotation) and the extrinsic contribution of the increased density of domain walls. The composition of (Na0.5Bi0.5)0.95Ca0.05Bi4Ti4O15 ceramics with x = 0.05 has the optimal performance with high TC of 655 °C, large d33 of 22 pC/N, high electrical resistivity ρ close to 107 Ω cm at 500 °C and especially excellent thermal stability of d33 only about 5% reduction after being annealed at 625 °C. The work effectively reveals the great potential of CNBT-5 ceramics for high-temperature piezoelectric applications.

Role of BO6 octahedral distortion on high temperature piezoelectric properties in Bi3-x(Li0.5Sm0.5)xTiNbO9

A series of bismuth layer structured ferroelectrics (BLSFs) Bi3-x(Li0.5Sm0.5)xTiNbO9 (abbreviated as BTNO-100xLS, x = 0, 0.01, 0.02, and 0.03) high temperature piezoelectric ceramics were prepared by solid state reaction sintering. The microstructure, piezoelectric properties, and electrical conductivity of the sintered ceramics were studied systematically. The introduction of (Li0.5Sm0.5)2+ ions does not change the bismuth layered structure obviously, but it will overmelt and affect its comprehensive properties with the increase of doping content. At last, the piezoelectric coefficient (d33) of ∼9.6 pC/N and the Curie temperature (Tc) is 921.3 °C, which shows good temperature stability and cycle stability, and the mechanical quality factor (Qm) reaches 2694.3 for x = 0.01 composition. These results show that BTNO-1LS is an excellent candidate for high temperature piezoelectric ceramics.

A Review on Bismuth Oxyhalide (BiOX, X=Cl, Br, I) Based Photocatalysts for Wastewater Remediation

Solar energy transformation over semiconductor-based photocatalysis is an ideal solution to environmental problems and future sustainability. Layered bismuth oxyhalides (BiOX, X = Cl, Br or I) are very attractive and promising photocatalysts in the environment fields. This review summarizes recent advances on the design of BiOX to enhance energy converting efficiency. Especially, the emerging techniques to enhance the photocatalytic behaviors of BiOX are discussed, including non-metal/metal doping, heterojunction engineering, carbon interfacing, coupling with noble metals, defect engineering, and morphology tuning. The application of BiOX composites in wastewater remediation is also reviewed in terms of organic photocatalytic oxidation and heavy metal ion photocatalytic reduction. Finally, the future chances and challenges of BiOX photocatalysts for practical application are summarized. In all, this review well underlies the innovative preparation of BiOX products for environment-related purposes.

Thickness dependent band structure of α-bismuthene grown on epitaxial graphene

Along with the great interest in two-dimensional elemental materials that has emerged in recent years, atomically thin layers of bismuth have attracted attention due to physical properties on account of a strong spin–orbit coupling. Thickness dependent electronic band structure must be explored over the whole Brillouin zone in order to further explore their topological electronic properties. The anisotropic band structures along zig-zag and armchair directions of α-bismuthene (α-Bi) were resolved using the two-dimensional mapping of angle-resolved photoemission spectra. An increase in the number of layers from 1- to 2-bilayers (BLs) shifts the top of a hole band on line to high wavenumber regions. Subsequently, an electron pocket on line and a hole pocket centred at point appears in the 3 BL α-Bi. Gapless Dirac-cone features with a large anisotropy were clearly resolved on point in the 1-BL and 2-BL α-Bi, which can be attributed to the strong spin–orbit coupling and protection by the nonsymmorphic symmetry of the α-Bi lattice.

Textured Bi4Ti3O12 Ceramics: One‐Step Spark Plasma Sintering and Their Single‐Crystal‐Like Polar Anisotropy

Texturing is the most effective way to engineer the performance of bismuth layer–structured ferroelectric (BLSF) ceramics by utilizing the strong anisotropy of grains, but the existing processing approaches are still complex. Herein, a one‐step spark plasma sintering (SPS) approach is demonstrated to prepare textured Bi4Ti3O12 (BiT) ceramics with high performance. The degree of orientation can be controlled from 57% to 95% by only adjusting the sintering temperature from 840 to 1000 °C. The largest spontaneous polarization (Ps) of ≈32.2 μC cm−2 is obtained in 95% <001> textured ceramics along the direction perpendicular to the SPS pressure, accompanied with the maximum electro‐strain of ≈0.14% and piezoelectric coefficient of 14.3 pC N−1. Moreover, under the same conditions of poling and illumination, the textured ceramics exhibit unique anisotropic photoresponse in which the photocurrent polarity is dependent on the testing orientations. In particular, a short‐circuit photocurrent density of 8.76 nA cm−2 is achieved along the direction of SPS pressure after positive poling, while the value goes to −79.4 nA cm−2 along direction perpendicular to the SPS pressure. These results are expected to provide a paradigm to achieve highly textured BLSF ceramics for electric and photoelectric applications.

Layered bismuth oxide/bismuth sulfide supported on carrageenan derived carbon for efficient carbon dioxide electroreduction to formate

Electrochemical reduction of carbon dioxide (CO2ER) into formate plays a crucial role in CO2 conversion and utilization. However, it still faces the problems of high overpotential and poor catalytic stability. Herein, we report a hybrid CO2ER electrocatalyst composed of layered bismuth sulfide (Bi2S3) and bismuth oxide (Bi2O3) supported on carrageenan derived carbon (Bi-CDC) prepared by a combined pyrolysis with hydrothermal treatment. In such 3D hybrid, layered Bi2O3 and Bi2S3 are uniformly grown on nanocarbon supports. Benefiting from strong synergistic effect between Bi2O3/Bi2S3 and nanocarbon, Bi-CDC-1:2 displays a high Faradic efficiency (FE) of >80% for formate production in the range of −0.9 V to −1.1 V with the maximum formate FE of 85.6% and current density of 14.1 mA·cm−2 at −1.0 V. Further, a positive onset potential of −0.5 V, a low Tafel slope of 112.38 mV·dec−1, and a slight performance loss during long-term CO2ER tests are observed on Bi-CDC-1:2. Experimental results shows that the better CO2ER performance of Bi-CDC-1:2 than that of Bi2O3 can be attributed to the strong interfacial interactions between nanocarbons and Bi2O3/Bi2S3. In situ ATR-FTIR measurements reveal that the rate-determining step in the CO2ER is the formation of HCOO* intermediated. Compared with carbon support, Bi-CDC-1:2 can promote the production of HCOO* intermediate and thus promoting CO2ER kinetic.

Outstanding optical properties of thermally grown (Bi2Se3)1-x (Bi2Te3)x thin films

Thin layers of (Bi2Se3)1-x(Bi2Te3)x samples were prepared by vacuum thermal evaporation technique. Starting materials are bulk alloys of good crystallinity. Characterization and optical properties of the synthesized films are discussed. Structure properties, surface features and roughness of the deposited films are probed via XRD, SEM and HRTEM techniques, which confirmed perfect crystallinity and nano-scalability of the samples. Transmission and reflection spectra attested that all prepared films have a growing transparency upon increasing the wavelength beyond the infra-red region, with optical band gap energy varies between 0.72 and 0.91 eV. Interesting absorption is detected in the visible light region. Enhancement of light transmission in layered bismuth chalcogenides is achieved through incorporation of Bi2Te3 into the (Bi2Se3)1-x(Bi2Te3)x system at x = 0.20. A maximum transmittance of 81.5% was observed in the IR region. The concerned materials showed high interest for transparent and highly conductive electrodes and also for flexible electronic devices.

Manipulating Excitonic Effects in Layered Bismuth Oxyhalides for Photocatalysis

Manipulating Excitonic Effects in Layered Bismuth Oxyhalides for Photocatalysis

Epitaxial Engineering Strategy to Amplify Localized Surface Plasmon Resonance and Electrocatalytic Activity Enhancement in Layered Bismuth Selenide by Phosphorus Functionalization

AbstractBismuth selenide (Bi2Se3) is an orderly layered material with large surface area and localized surface plasmon resonance (LSPR). The electrocatalytic profile of Bi2Se3 has been least explore for energy storage applications since its pristine form is handicapped with limited electrical conductivity. Here we report an epitaxial engineering strategy to manipulate the weak van der Waals forces to expand the interlayer spacing by intercalating phosphorus (P) atom by chemical vapor deposition (CVD) method. The obtained P intercalated Bi2Se3 (P@Bi2Se3) exhibited towering LSPR, increased carrier density bestowing ample active sites, enhanced ion diffusion and plentiful channels for the exodus of electrolyte. The potential of P@Bi2Se3 was examined for energy storage application which exhibited battery like behavior with a specific capacity (Cs) of 194 C g−1 at 3 A g−1 current density against 121 C g−1 by Bi2Se3/NF under identical condition and restored 88 % of its initial specific capacity even after 5000 charge/discharge cycles. The hybrid supercapacitor (HSC) assembled using P@Bi2Se3 and O, N, S@AC as positive and negative electrodes exhibited a considerable specific capacitance, high specific energy (Es) and specific power (Ps) with excellent stability for 10000 charge/discharge cycles. The surface and interfacial engineering strategy proposed here can be extended to tune plasmonic resonance and charge carrier energy density for the successful implementation of Bi2Se3 beyond energy storage applications.

Hydrothermal preparation and visible-light photocatalytic activity of bismuth layer structure Na0.5Bi2.5Nb2O9 nanoplates

Nanoparticles of bismuth-layered ferroelectric and photocatalytic material, Na0.5Bi2.5Nb2O9, have been prepared by hydrothermal method synthesis, the raw materials include Bi(NO3)3, NaOH and Nb2O5. The phases and morphologies of the samples are characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic performance of the Na0.5Bi2.5Nb2O9 powders were evaluated by degradation of methylene blue(MB) molecules (λ>400 nm). The results show that the phases of Na0.5Bi2.5Nb2O9 particle is pure orthorhombic bismuth layer structure at 160 °C and 10 h. The morphology of the sample is flake-like, the thickness size is 25 nm, and the edge size is 200 nm. Na0.5Bi2.5Nb2O9 sample has excellent light response performance in the ultraviolet-visible wavelength range, with a band gap of 2.55 eV, and it exhibits photocatalytic performance for photocatalytic decomposition of MB under ultraviolet-visible light irradiation. As novel of visible-light-driven photocatalysts, Na0.5Bi2.5Nb2O9 with a two-layer Aurivillius structure has a great potentially application in environment-protection field.

Fabrication and enhanced photoelectric properties of a novel Bi9O7.5S6/CdS composite film.

Layered bismuth oxychalcogenides have been demonstrated as potential candidates for high-speed and low-power electronics due to their outstanding environmental stability and high carrier mobility, but the photoelectric performance of bulk species is still far from satisfactory. Herein, a novel Bi9O7.5S6/CdS composite film with a type-II heterojunction has been successfully prepared by combining chemical bath deposition (CBD) and spin-coating technologies. The structure, morphology, optical and photoelectric properties of the samples were investigated systematically. The photoelectric current of the Bi9O7.5S6/CdS composite film was obtained as 32.49 μA cm-2 at 1 V, which is about 13.9-fold and 3.3-fold higher than those of bare Bi9O7.5S6 and CdS. An enhanced photoelectric response and photostability were achieved in the Bi9O7.5S6/CdS composite film, and can be appropriately attributed to the improved separation and transfer of photogenerated carriers driven by the type-II heterojunction. This work offers a promising route to develop high-performance visible-light photoelectric devices with type-II heterojunctions.

Self-biased photodetector using 2D layered bismuth triiodide (BiI3) prepared using the spin coating method.

Layered bismuth triiodide (BiI3) is a 2D material that has emerged as an ideal choice for optical sensors. Although BiI3 has been prepared using vacuum-based deposition techniques, there is a dearth of research studies on synthesizing this material using chemical route. The present work uses a facile spin coating method with varying rotation speeds (rpm) to fabricate BiI3 material thin films for photodetection applications. The structural, optical, and morphological study of BiI3 thin films prepared at 3000-6000 rpm were investigated. XRD analysis indicates formation of BiI3 films and revealed that BiI3 has a rhombohedral crystal structure. FESEM analysis showed that BiI3 films prepared at different rpm are homogeneous, dense, and free from cracks, flaws, and protrusions. In addition, films show an island-like morphology with grain boundaries having different grain sizes, micro gaps, and the evolution of the granular morphology of BiI3 particles. The UV spectroscopy and photoluminescence analysis revealed that BiI3 films strongly absorb light in the visible region of spectra with a high absorption coefficient of ∼104 cm-1, have an optical band gap of ∼1.51 eV. A photodetector was realised using fabricated BiI3 film obtained at an optimum spin speed of 4000 rpm. It showed rapid rise and decay times of 0.4 s and 0.5 s, a responsivity of ∼100 μA W-1, external quantum efficiency of 2.1 × 10-4%, and detectivity of ∼3.69 × 106 Jones at a bias voltage of 0 V. Our results point towards a new direction for layered 2D BiI3 materials for the application in self-biased photodetectors.

Cu/W Co-doped CaBi2Nb2O9 piezoelectric ceramics on structural and electrical properties

This article reports the significantly improved piezoelectric and ferroelectric properties of Cu/W co-doped Ca2Bi2Nb2-x(Cu1/4W3/4)xO9 (CBNCW-x, where 0 ≤ x ≤ 0.150) high Curie temperature lead-free piezoelectric ceramics. The crystal structure, microstructure, and electric properties of CBNCW-x ceramics have been systematically analyzed. The results show that ceramic samples have a bismuth layered structure of m= 2, which is a single-phase of CBN. The ceramic grains show the typical plate-like structure of the bismuth layer. Cu/W co-doped CBN ceramics increased the distortion of NbO6 octahedron, and significantly enhanced the piezoelectric constant and the remnant polarization. When x = 0.075, it shows better comprehensive properties with an excellent d33 of 13.8 pC/N, a high remnant polarization of 12.10 μC/cm2, the Tc of 918 °C, a dielectric loss value of 0.57%, and the Qm value of 7099. Moreover, CBNCW-0.075 ceramic simple maintains the d33 of 12.7 pC/N after annealing 900 °C for 30 min, which shows good high-temperature stability. It suggests that the Cu/W co-doped CBN ceramics have good application prospects in the high-temperature piezoelectric field.

Effects of topological band structure on thermoelectric transport of bismuthene

Two-dimensional bismuth (Bi) layer, known as bismuthene, exhibits $Z2$ topological bulk states due to large spin-orbit coupling that inverts the bands. Using the tight-binding method, we calculate the band structure of buckled bismuthene to understand its topological and trivial phases. We determine the thermoelectric properties for some considered phases, incorporating the edge states contribution, by using the linearized Boltzmann transport equation with a constant relaxation time approximation. It is shown that the thermoelectric figure of merit, $ZT$, actually drops in undoped topological bismuthene due to the edge effects. Surprisingly, the topological edge states enhance $ZT$ at large doping with the Fermi energy near the bottom of bulk bands when bismuthene is nearly metallic.

Improved photodegradation efficiency in Fe3+-doped Bi3TiNbO9 nanosheets through oxygen vacancies introduction and ferroelectric polarization enhancement simultaneously

Suffering from wide bandgaps and poor charge carrier mobility, most of the ferroelectric photocatalysts are still faced with low efficiency in spite of the advanced intrinsic ferroelectric polarization. Herein we proposed a simple Fe3+-doping strategy to induce oxygen vacancies and enhance ferroelectric polarization in Bi3TiNbO9 nanosheets simultaneously, realizing band structure modulation and charge carrier kinetics steering. Combining DFT calculations and systematic experimental characterizations, it was demonstrated that the introduction of Fe not only reduce the bandgaps but also improve electron-hole separation. The promoted carrier transport and increased carrier density was related to the Fe3+/Fe2+ redox cycle and oxygen vacancies (OVs) arising from the substitution of Ti4+ with Fe3+. More importantly, the enlarged ferroelectric polarization strength after doping verified by hysteresis loop can provide further driving force for charge carrier migration. Benefitting from these optimized properties, under the optimum doping concentration, the photocatalytic degradation rate of antibiotic tetracycline hydrochloride and organic dye rhodamin B under visible light were about 1.6 times and 2.1 times of that in pure Bi3TiNbO9 respectively, outperforming the benchmark P25 and the majority of bismuth layer structured ferroelectrics. This work shed light on the feasibility of defect engineering and ferroelectric polarization modulation for efficient ferroelectric photocatalysts development.

Ultrathin epitaxial Bi film growth on 2D HfTe2 template

Among ultrathin monoelemental two-dimensional (2D) materials, bismuthene, the single layer of heavier group-VΑ element bismuth (Bi), has been predicted to have large non trivial gap. Here, we demonstrate the growth of Bi films by molecular beam epitaxy on 2D-HfTe2 template. At the initial stage of Bi deposition (1–2 bilayers, BL), both the pseudocubic Bi(110) and the hexagonal Bi(111) phases are formed. When reaching 3 BL Bi, a transformation to pure hexagonal Bi(111) occurs. The electronic band structure of 3 BL Bi(111) films was measured by angle-resolved photoemission spectroscopy showing very good matching with the density functional theory band structure calculations of 3 BL free standing Bi(111). The grown Bi(111) thin film was capped with a protective Al2O3 layer and its stability under ambient conditions, necessary for practical applications and device fabrication, was confirmed by x-ray photoelectron spectroscopy and Raman spectroscopy.

Bismuth Pelvic X-Ray Shielding Reduces Radiation Dose Exposure in Pediatric Radiography.

Background Radiation using conventional X-ray is associated with exposure of radiosensitive organs and typically requires the use of protection. This study is aimed at evaluating the use of bismuth shielding for radiation protection in pediatric pelvic radiography. The effects of the anteroposterior and lateral bismuth shielding were verified by direct measurements at the anatomical position of the gonads. Methods Radiation doses were measured using optically stimulated luminescence dosimeters (OSLD) and CIRS ATOM Dosimetry Verification Phantoms. Gonad radiographs were acquired using different shields of varying material (lead, bismuth) and thickness and were compared with radiographs obtained without shielding to examine the effects on image quality and optimal reduction of radiation dose. All images were evaluated separately by three pediatric orthopedic practitioners. Results Results showed that conventional lead gonadal shielding reduces radiation doses by 67.45%, whereas dose reduction using one layer of bismuth shielding is 76.38%. The use of two layers of bismuth shielding reduces the dose by 84.01%. Using three and four layers of bismuth shielding reduces dose by 97.33% and 99.34%, respectively. Progressively lower radiation doses can be achieved by increasing the number of bismuth layers. Images obtained using both one and two layers of bismuth shielding provided adequate diagnostic information, but those obtained using three or four layers of bismuth shielding were inadequate for diagnosis. Conclusions Bismuth shielding reduces radiation dose exposure providing appropriate protection for children undergoing pelvic radiography. The bismuth shielding material is lighter than lead, making pediatric patients more comfortable and less apt to move, thereby avoiding repeat radiography.