Orientation-controlled phase transformation of Bi2O3 during oxidation of electrodeposited Bi film

High-temperature fluorite structure Bi₂O₃ is a well-known solid electrolyte owing to its high oxygen ion conductivity. In this study, Bi₂O₃ thin film was prepared by the oxidation process of the electrodeposited metallic Bi film. The crystal structures of the oxidized Bi films varied with the applied voltages during the electroplating process. Pure α-Bi₂O₃ was obtained when the oxidation was conducted for the metallic Bi film electrodeposited at −0.1 V. Only β-Bi₂O₃ was observed as a −0.5 V electrodeposited Bi film was oxidized. The crystal structure of Bi₂O₃ obtained by oxidation of metallic Bi film may dominantly be affected by the orientation of as-electrodeposited Bi film. Such kind of process is favorable to the preparation of functional ceramic with specific crystal structure.     

Variants of the Bi6TiP2O16 structure: The preparation and crystal structure of the isomorph Bi6(Mn0.6Bi0.4)P2O15

Compounds with the composition Bi₆(Bi_1−yM_y)X₂O_16−z, M = transition metal or Pb, X = P, V, As, display pseudo-tetragonal crystal systems. They are, however, monoclinic with space group I2 and the heavy atom positions mimic the δ-Bi₂O₃ structure. The title compound is monoclinic, a = 11.284(2) Å, b = 5.4259(11) Å, c = 11.112(2) Å, β = 96.25(3)°, I2, Z = 2. Least-squares refinement of single-crystal X-ray diffraction data on F² converged to R1 = 0.050, wR2 = 0.130. The crystal is twinned by two-fold rotation about [0 1 0] and each twin consists of its inverted component forming a racemate. The structure consists of chains of edge sharing (OBi₄) tetrahedra parallel to [1 0 −1]. The chains are bridged parallel to [1 0 1] by linked PO₄ tetrahedra and (Mn/Bi)O₆ octahedra parallel to [1 0 −1], into a three-dimensional structure. The lone-pair electrons of adjacent Bi atoms along the chain point in opposite directions along the b-axis. The Bi atoms are in distorted trigonal prismatic coordination that has one or two faces capped. The BiO bond lengths vary from 2.08(5) to 3.05(2) Å. The Mn/Bi atoms are disordered around the two-fold axis. Three oxygen atom sites contain vacancies.     

Photocatalytic degradation of an azo dye using Bi3.25M0.75Ti3O12 nanowires (M = La,Sm, Nd,and Eu)

Bi_3.25M_0.75Ti₃O₁₂ (BMT, M = La, Sm, Nd, and Eu) nanowires were synthesized through simple hydrothermal route and their structural and photocatalytic properties were investigated. XRD results indicated that these compounds are of layered perovskites structure. In addition, the band gaps of Bi_3.25La_0.75Ti₃O₁₂ (BLT), Bi_3.25Sm_0.75Ti₃O₁₂ (BST), Bi_3.25Nd_0.75Ti₃O₁₂ (BNT), and Bi_3.25Eu_0.75Ti₃O₁₂ (BET) were estimated to be about 2.403, 2.594, 2.525, and 2.335 eV, respectively. Their photocatalytic activities were evaluated by photocatalytic degradation of methyl orange (MO) under visible light irradiation (λ > 420 nm). Bi_3.25M_0.75Ti₃O₁₂ (M = La, Sm, Nd, and Eu) showed markedly higher catalytic activity compared to traditional N doped TiO₂ (N-TiO₂) and pure bismuth titanate (Bi₄Ti₃O₁₂, BIT) for MO photocatalytic degradation under visible light irradiation. The high photocatalytic performance of Bi_3.25M_0.75Ti₃O₁₂ photocatalysts could be attributed to the strong visible light absorption and the recombination restraint of the e^?/h⁺ pairs resulting from doping of rare earth metal ions. Furthermore, BET nanowires exhibited the highest photocatalytic activity.     

Low-temperature firing and microwave dielectric properties of MgTiO3 ceramics with Bi2O3–V2O5

The effects of Bi₂O₃–V₂O₅ additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO₃ Ceramics were investigated. The Bi₂O₃–V₂O₅ addition lowered the sintering temperature of MgTiO₃ ceramics effectively from 1400 to 875 °C due to the liquid-phase effect. The microwave dielectric properties were found to strongly correlate with the amount of Bi₂O₃–V₂O₅ addition. The saturated dielectric constant decreased and the maximum Qf values increased with the increasing V₂O₅ content, which is attributed to the variation of the second phase including Bi₂Ti₂O₇, Bi₄V_1.5Ti_0.5O_10.85 and BiVO₄. At 875 °C, MgTiO₃ ceramics with 5.0 mol% Bi₂O₃–7 mol% V₂O₅ gave excellent microwave dielectric properties: ε_r = 20.6,Qf = 10420 GHz (6.3 GHz).     

Lithium solubility limit in ZnGa2O4:Bi0.0013+,Li+ phosphor

The lithium solubility limit, photoluminescence (PL) and photoluminescence excitation (PLE) properties of lithium ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor have been investigated. A LiGaO₂ second phase began to appear from 3 mol% Li⁺ ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor. The enhanced brightness of blue (λ_ex = 254 nm) and white (λ_ex = 315 nm) colors of bismuth ions doped ZnGa₂O₄:Bi³⁺,Li⁺ phosphor was assigned to the formation of LiGaO₂. Bi³⁺ activated lithium zinc gallate phosphor showed a more enhanced PLE peak around 315 nm than that of lithium zinc gallate phosphor when λ_em = 520 nm. Thus, we observed that the PL intensity of ZnGa₂O₄:Bi³⁺,Li⁺ phosphor with λ_em = 520 nm was much greater than that of ZnGa₂O₄:Li⁺ phosphor. Also, ZnGa₂O₄:Bi³⁺,Li⁺ phosphor exhibited a shorter decay time than that of ZnGa₂O₄:Li⁺ phosphor by about a factor of about 2.     

Preparation,characterization and photocatalytic activity of Bi2O3–MgO composites

A series of Bi₂O₃–MgO composites were synthesized by solvent-thermal method. It was found that the Bi₂O₃–MgO composites perform much better than TiO₂ (P25), Bi₂O₃ and MgO in the photocatalytic degradation of rhodamine B (RhB) in the presence of HCl and under irradiation of visible light (λ > 400 nm). The effects of Bi/Mg molar ratio, crystallization temperature of Bi₂O₃–MgO and reaction conditions on photocatalytic activity were studied. The best performance was observed over the composite with Bi:Mg molar ratio equal to 2:1 that had been subject to crystallization at 120 °C for 20 h. In addition, the photocatalytic efficiency of the composite can be significantly enhanced by the presence of hydrochloric acid. The prepared samples were characterized by XRD and UV–vis DRS techniques. The relationships between the structure and photocatalytic performance of the as-prepared Bi₂O₃–MgO samples were also investigated.     

Physical and spectroscopic properties of multi-component Na2O–PbO–Bi2O3–SiO2 glass ceramics with Cr2O3 as nucleating agent

Transparent glass ceramics, synthesized from melt quenching followed by heat treatment, of the composition 10Na₂O–30PbO–10Bi₂O₃–(50 − x)SiO₂:xCr₂O₃ (mol%), where 0 ⩽ x ⩽ 0.5, were characterized with XRD, DTA, SEM and EDS. Physical and spectroscopic studies, viz., optical absorption, electron paramagnetic resonance (EPR), FTIR and Raman were investigated. The characterization of the host glass ceramic has revealed that the formation of a major phase of sodium silicate along with two minor phases such as lead silicate and bismuth oxide. By integrating Cr₂O₃ to the host glass additional crystal phases viz., NaCrO₂, Na₂Cr₂O₇ and Pb(CrO₄) which are the complexes of Cr³⁺ and Cr⁶⁺ ions were also developed. As the concentration of nucleating agent is increased, a part of the Cr⁶⁺ ions is found to reduce in to Cr³⁺ ions. Spectroscopic studies have revealed that with an increase in the concentration of Cr₂O₃ from 0.1 to 0.5 mol%, there is a gradual increase in the intensity of vibrational modes of various asymmetric structural units of silicate, bismuthate and chromate in the glass ceramic network at the expense of symmetrical structural units. The analysis of the results of these studies has indicated that in the samples containing higher concentration of Cr₂O₃, chromium ions exists predominantly in Cr³⁺ state and occupy the octahedral positions in glass ceramic matrix and such glass ceramic samples are suitable for lasing action.     

Crystallization of nanosized Aurivillius phase Bi2W2O9 from amorphous precursor

Nanoparticles of bismuth layered Aurivillius phase, Bi₂W₂O₉, have been synthesized by annealing of precursor prepared by high energy milling in ball mill. The obtained powders have been investigated using the XRD, TEM, SEM, diffuse reflectivity, Raman and infrared spectroscopy. The results show that mechanochemical activation allows obtaining Bi₂W₂O₉ at much lower temperatures than those required in a conventional solid state reaction or synthesis through a complex organic precursor. As a result, material with smaller grain size can be obtained. Therefore this synthesis method is the best route to enhance photocatalytic activity of Bi₂W₂O₉. Our results also show that milling time has great impact on the crystallization mechanism. Bi₂W₂O₉ crystallizes easily already at 600 °C from precursor milled by 8 h. However, prolong milling time results in stabilization of an unknown phase or phases, which crystallize below 700 °C, and transform into the well-known Bi₂W₂O₉ phase after annealing at 750 °C.     

Gd2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Gd₂O₃ (0–0.8 wt.%)-doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state process. The effects of Gd₂O₃ on the microstructure, the dielectric, ferroelectric and piezoelectric properties were investigated. X-ray diffraction (XRD) data shows that Gd₂O₃ in an amount of 0.2–0.8 wt.% can diffuse into the lattice of BNKT18 ceramics and form a pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain size of BNKT18 ceramics decreases with the increase of Gd₂O₃ content; in addition, all the modified ceramics have a clear grain boundary and a uniformly distributed grain size. At room temperature, the ferroelectric and piezoelectric properties of the BNKT18 ceramics have been improved with the addition of Gd₂O₃, and the BNKT18 ceramics doped with 0.4 wt.% Gd₂O₃ have the highest piezoelectric constant (d₃₃ = 137 pC/N), highest relative dielectric constant (ε_r = 1023) and lower dissipation factor (tan δ = 0.044) at a frequency of 10 kHz. The BNKT18 ceramics doped with 0.2 wt.% Gd₂O₃ have the highest planar coupling factor (k_p = 0.2463).     

Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT), have been synthesized on Pt/Ti/SiO₂/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O₂ ambient are consisted of iteration of two unit cells of Bi₃TiNbO₉ and one unit cell of Bi₄Ti₃O₁₂. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O₂ flow rate from 0.5 to 1.5 L/min, both remanent polarization P_r and coercive electric field E_C increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O₂ ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of P_r = 23.5 μC/cm² and E_C = 135 kV/cm.     

Structure and electrical properties of Er2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Er₂O₃ (0–0.8 wt.%)-doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Er₂O₃ on the microstructure and electrical properties were investigated. X-ray diffraction (XRD) data shows that Er₂O₃ in an amount of 0.2–0.8 wt.% can diffuse into the lattice of the BNKT18 ceramics and form the pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain sizes of BNKT18 ceramics decrease with the increase of Er₂O₃ content; in addition, the modified ceramics have the clear grain boundary and a uniformly distributed grain size. At room temperature, the electrical properties of the BNKT18 ceramics have been improved with the addition of Er₂O₃, and the BNKT18 ceramics doped with 0.6 wt.% Er₂O₃ have the highest piezoelectric constant (d₃₃ = 138 pC/N), the highest planar coupling factor (k_p = 0.2382), the highest remnant polarization (P_r = 25.2 μC/cm²), the higher relative dielectric constant (ε_r = 936) and lower dissipation factor (tanδ = 0.047) at a frequency of 10 kHz. Moreover, the T_m and T_d of the samples increase with the addition of Er₂O₃.     

Photoelectrochemical characterization of Bi2Se3 thin films deposited by SILAR technique

Bi₂Se₃ thin films have been deposited by simple and less investigated successive ionic layer adsorption and reaction (SILAR) technique onto fluorine-doped tin oxide (FTO) coated glass substrates at room temperature (27 °C). The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies indicate that Bi₂Se₃ thin films are nanocrystalline. These films are used for photoelectrochemical (PEC) characterization in cell with configuration as n-Bi₂Se₃/0.1 M polysulfide/C. The studies such as current–voltage characteristics in dark and light, photovoltaic power output, transient photoresponse, and capacitance–voltage have been carried out. The study reveals that fill factor and power conversion efficiency of the cell are low (0.43 and 0.032%, respectively).The flat bond potential is found to be −0.04 V (SCE).     

Novel Mo/Bi2MoO6/Bi3ClO4 heterojunction photocatalyst for ultra-deep desulfurization of thiophene under simulated sunlight irradiation

In the present work, a visible-light-driven Mo/Bi₂MoO₆/Bi₃ClO₄ heterojunction photocatalyst was fabricated via the Pechini sol–gel process. The type and amount of gelling agent, chelating agent and mole ratio of chelating agent to total metals were balanced to generate ultrafine nanoparticles. The Mo/Bi₂MoO₆/Bi₃ClO₄ nanocomposite as a novel photocatalyst not only exhibited an excellent visible-light photocatalytic desulfurization performance of thiophene (~97%), but also had better photodesulfurization efficiency than Mo/Bi₂MoO₆ and Bi₃ClO₄ nanostructures. The ultra-deep photocatalytic desulfurization performance of the Mo/Bi₂MoO₆/Bi₃ClO₄ nanocomposite can be attributed to the strong visible-light absorption, unique nanostructures, high separation and low recombination of electron–hole pairs due to the as-formed heterojunctions. Furthermore, a photocatalytic desulfurization mechanism was elucidated via radical trapping experiments, which revealed that the ^?O₂^? and ^?OH radicals play a key role in the photocatalytic desulfurization process.     

PH-induced structural evolution,photodegradation mechanism and application of bismuth molybdate photocatalyst

In this work, we have elucidated the pH-induced structural evolution of bismuth molybdate photocatalyst based on a hydrothermal synthesis route. With increasing the pH value of precursor solution, pure Bi₂MoO₆ was synthesized at pH 2–5, Bi₂MoO₆-Bi₄MoO₉ mixture was obtained at pH 7–9, pure Bi₄MoO₉ was obtained at pH 11, and pure α-Bi₂O₃ was derived at pH 13. The as-derived samples mainly present particle-like shapes but with different particle sizes (except the observation of Bi₂MoO₆ nanowires in sample S-pH9). The photocatalytic performances between the samples were compared via the degradation of methylene blue (MB) under irradiation of simulated sunlight. The Bi₂MoO₆ sample synthesized at pH 2 exhibited the highest photodegradation performance (η(30 min) = 89.8 %, k_app = 0.05007 min^?1) among the samples. The underlying photocatalytic mechanism and degradation pathways of MB were systematically analyzed. Moreover, the photodegradation performance of the Bi₂MoO₆ photocatalyst was further evaluated at different acidic-alkaline environments as well as in degrading various color and colorless organic pollutants, which provides an important insight into its practical application.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Influence of Ga3+ ions on spectroscopic and dielectric features of multi component lithium lead boro bismuth silicate glasses doped with manganese ions

Multi-component glasses of the chemical composition 19.5Li₂O–20PbO–20B₂O₃–30SiO–(10 − x)Bi₂O₃–0.5MnO:xGa₂O₃ with 0 ≤ x ≤ 5.0 have been synthesized. Spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties were investigated. Optical absorption and ESR spectral studies have indicated that managanese ions do exist in Mn³⁺ state in addition to Mn²⁺ state in the samples containing low concentration of Ga₂O₃. The IR and Raman studies indicated increasing degree of disorder in the glass network with the concentration of Ga₂O₃ up to 3.0 mol%. The dielectric constant, loss and ac conductivity are observed to increase with the concentration of Ga₂O₃ up to 3.0 mol%. The quantitative analysis of the results of dielectric properties has indicated an increase in the insulating strength of the glasses as the concentration of Ga₂O₃ is raised beyond 3.0 mol%. This has been attributed to adaption of gallium ions from octahedral to tetrahedral coordination.     

Heteroepitaxial growth of δ-Bi2O3 thin films on CaF2(1 1 1) by chemical vapour deposition under atmospheric pressure

We have succeeded in achieving the heteroepitaxial growth of a δ-Bi₂O₃ thin film on a CaF₂(1 1 1) substrate by means of chemical vapour deposition under atmospheric pressure. The film grew with a strong (1 1 1) orientation. From X-ray pole figures, it was observed that the δ-Bi₂O₃ film grew on the CaF₂(1 1 1) substrate with 60° rotational in-plane domains. The growth mode was of a 3D island type, and the grain size decreased with increasing oxygen pressure during the δ-Bi₂O₃ film growth, improving the overall surface smoothness.     

From Bi4V2O11 to Li28Bi4V2O11 by electrochemical lithium insertion:: versatile applications in lithium batteries

The compound Bi₄V₂O₁₁ has been tested as a positive electrode in room temperature electrochemical lithium cells. When the cells are discharged down to 0.5 V the reaction of Bi₄V₂O₁₁ with 28 lithium ions develops a theoretical specific capacity of 700 A h kg⁻¹. Hence, this compound could be used as cathode in primary lithium batteries. Besides, we consider the fact that in the low voltage region (1.3–0.5 V) Li₂₈Bi₄V₂O₁₁ develops about 360 A h kg⁻¹ at 0.7 V, and, therefore, this material is proposed as a negative electrode in lithium ion batteries. The mechanism of the reaction of Bi₄V₂O₁₁ with 28 lithium ions is not yet fully understood, although some guidelines can be given.     

Y4Al2O9 hierarchically nanostructured microspheres assembled with nanosheets: Microwave-solvothermal synthesis combined with thermal treatment and photocatalytic property

We have developed a microwave-solvothermal synthesis combined with thermal treatment method for the preparation of Y₄Al₂O₉ hierarchically nanostructured microspheres assembled with nanosheets. First, a simple microwave-assisted solvothermal method is used to prepare the precursor using Y(NO₃)₃ and Al(NO₃)₃ at 200 °C in mixed solvents of water and N,N-dimethylformamide (DMF) without any surfactant. Then, thermal treatment of the precursor at 900 °C in air for 2 h is performed to obtain Y₄Al₂O₉ hierarchically nanostructured microspheres, during which the morphology of the precursor can be well preserved. The samples are characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The photocatalytic activity of as-prepared Y₄Al₂O₉ hierarchical microspheres over phenol is investigated and the degradation rate of phenol is up to 91.2% in a period of 240 min.     

Thermoelectric properties of Bi2O2Se

Bi₂O₂Se was synthesized from Bi₂Se₃ and Bi₂O₃ by solid state reaction in an evacuated quartz ampoule. The product crystallizes in the tetragonal type lattice and X-ray pattern displays lines of the Bi₂O₂Se only. Samples for thermoelectric property measurements were prepared using hot pressing in rectangular graphite dies. The samples were characterized by the measurements of Seebeck coefficient, electrical conductivity and thermal conductivity as a function of temperature. From the experimental data we calculate the dimensionless figure of merit ZT that for a non-optimized material approaches the value 0.2 at 800 K.