Quantitative WDXS Microanalysis of Bismuth-Based BaBi4Ti4O15 Perovskites Doped with Nb and Fe

 Quantitative electron-probe microanalysis was used to determine the chemical composition of an Fe- and Nb-doped bismuth-based BaBi₄Ti₄O₁₅ perovskite compound. Elemental concentrations of Fe, Nb, Bi, Ba and Ti were accurately measured using wavelength-dispersive X-ray spectroscopy that was optimised for the analysis of a complex oxide matrix containing minor concentrations of dopants. Measurements were performed with a JEOL JXA 840A electron probe microanalyser at 20 and 26 kV, 50 nA beam current, 100 s maximum counting time and 0.3% preset counting deviation (σ_c) using both PET and LiF crystals. K-ratios were quantified by the ZAF and the φ(ρz) PAP matrix-correction procedures. The results showed that dopants incorporate into the BaBi₄Ti₄O₁₅ at Ti^4 + sites according to the Ba_1−4XBi_4 + 4XTi_4−4XFe_4XO₁₅ and Ba_1 + 4XBi_4−4XTi_4−4XNb_4XO₁₅ solid-solution formulae. The majority of the excess charge introduced by the substitution of Ti^4 + with Fe^3 + or Nb^5 + is compensated for the change in the Ba^2 +/Bi^3 + ratio.     

Crystal structure and dielectric properties of the mixed Aurivillius phase Bi7Ti4NbO21

The crystal structure of the ferroelectric mixed Aurivillius phase Bi₇Ti₄NbO₂₁ was determined for the first time by X-ray diffractometry using a single crystal obtained by a flux method in Bi₂O₃ excess. It can be described as a regular stacking of double and triple perovskite-type slabs interleaved by Bi₃O₂ layers along the a axis. Nb is located in the double perovskite-type layers only with a random Nb/Ti distribution whereas the octahedral sites within the triple perovskite-type layers are occupied by Ti only. The thermal evolution of the dielectric constant between room temperature and 900 °C show two phase transitions at 650 and 830 °C. Combined analyses of experimental data support that the highest transition temperature corresponds to the Curie temperature, whereas the lowest one could be assigned to a phase transition within the orthorhombic symmetry by a change of the space group.     

Atomic Simulations of Aurivillius Oxides: Bi3TiNbO9, Bi4Ti3O12, BaBi4Ti4O15 and Ba2Bi4Ti5O18 Doped with Pb,Al, Ga,In, Ta

The Aurivillius oxides were originally of interest for their ferroelectric properties and have recently been explored in the field of oxide ion conductivity. Atomistic simulation methods have been carried out for Bi₃TiNbO₉, Bi₄Ti₃O₁₂, BaBi₄Ti₄O₁₅ and Ba₂Bi₄Ti₅O₁₈ doped with Pb, Al, Ga, In, Ta to determine defect energy in the materials by employing efficient energy minimization procedures. The calculations rest upon the specification of an interatomic potential model, which expresses the total energy of the system as a function of the nuclear coordinates. The Born model framework, which partitions the total energy into long‐range Coulombic interactions and a short‐range term to model the repulsions and van der Waals forces between electron charge clouds, is employed. This is embodied in the GULP simulation code. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Bi and Ta sites. Trivalent dopants (Al, Ga, In) and Pb are more favorable on the Bi site, whereas Ta dopants preferentially occupy the Ti site.     

Synthesis,characterization and photocatalytic properties of nanoparticles CuAl2O4 by Pechini method using Taguchi statistical design

In the present work nano crystalline copper aluminate (CuAl₂O₄) has been synthesized by the Pechini method using aqueous solutions containing corresponding metal nitrates. A Taguchi L₄ statistical design was employed for investigating the most effective factors on the synthesis conditions and their interactions and production optimization. Nano crystalline CuAl₂O₄ particles with crystal size between 17 and 26 nm were obtained. The product characterized by XRD, FT-IR, DLS and TGA. The morphological properties have investigated using SEM. The photocatalytic degradation was investigated using methyl orange under the irradiation of visible light.     

Synthesis and characterization of CaBi4Ti4O15 thin films annealed by microwave and conventional furnaces

CaBi₄Ti₄O₁₅ thin films were deposited by the polymeric precursor method and crystallized in a domestic microwave oven and conventional furnace. The films obtained for microwave energy are well-adhered, homogeneous and with good specularity when treated at 700 ^°C for 10 min. The microstructure and the structure of the films can be tuned by adjusting the crystallization conditions. When microwave oven is employed, the films presented bigger grains with mean grain size around 80 nm. For comparison, films were also prepared by the conventional furnace at 700 °C for 2 h.     

Studies of dielectric characteristics of BaBi2Nb2O9 ferroelectrics prepared by chemical precursor decomposition method

BaBiNb₂O₉ (BBN) powders in the nanometer range were prepared by chemical precursor decomposition method (CPD). TG–DTA showed that precursor sample got freed from organic contaminants at 575 °C. XRD showed that a single phase with the layered perovskite structure of BBN was formed after calcining at 600 °C. No intermediate phase was found during heat treatment at and above 600 °C. The crystallite size (D) and the effective strain (η) were found to be 26 nm and 0.000867, respectively, while the particle size obtained from TEM was 28 ± 2 nm. SEM revealed that the average grain size after sintering at 900 °C for 4 h was ∼1.67 μm. A relative density of ∼93% was obtained using a two-step sintering process at moderate pressure. Dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C and frequencies from 1 kHz to 5 MHz. Strong dispersion of the complex relative dielectric constant was observed including typical relaxor features such as shift of permittivity maximum with frequency and broadening of the peak maximum. The high dielectric constant of 545 measured at 100 kHz and other properties of BBN ceramics were compared to that of BBN prepared by other conventional methods and found to be superior.     

Structural and dielectric characterization of LiNbO3 nano-size powders obtained by Pechini method

Lithium niobate is an artificially synthesized material with wide technological applications, due to its numerous physical properties, such as: ferroelectricity, birefringence and large pyroelectric, piezoelectric, non-linear, acousto-optic, electro-optic and photo-elastic coefficients. It also exhibits very strong bulk photovoltaic and photo refractive effects. In the present work, LiNbO₃ powders were prepared by the Pechini (sol?Cgel) method. The heat-treatment of the base amorphous powders, at 450?°C promotes the formation of LiNbO₃ crystalline phase. The electrical characterization, in function of the heat-treatment time, shows that the dc conductivity depends on the quantity of crystalline phase, which increases with the increase of heat-treatment time. The sample treated for 96?h shows a dielectric constant value of ~35, at low frequencies. A dielectric relaxation phenomenon independent of the temperature of measurement was detected in the samples treated at 48 and 96?h, shifting to higher frequencies with the increase of the heat-treatment time.     

Electrical anisotropy in the hot-forged CaBi4Ti4O15 ceramics

Textured CaBi₄Ti₄O₁₅ (CBT) ceramics have been fabricated via a hot-forging technique. The effect of grain orientation on the dielectric and electrical properties is studied by impedance (Z¹) and modulus (M¹) spectroscopy. The degree of orientation (F) calculated from X-ray diffraction pattern is found to be 89.4% along the c-axis of the crystal structure. The permittivity was measured along both perpendicular and parallel directions of the forging axis. The ratio of permittivity along perpendicular to parallel direction is found to be ～3 at the Curie temperature of 797 °C. The non-superimposition of the normalized Z″ and M″ vs. frequency plot revealed the conduction in the material is localized and deviate from ideal Debye behavior. The power law exponent n of the material has been explained on the basis of jump relaxation model and revealed the conduction through grain boundary. Activation energy (E_a) is obtained from Arrhenius plots of the dc conductivity for both the ceramics and it is found to be 0.89 eV and 0.78 eV for CBT (∥) and CBT (⊥), respectively.     

Synthesis and Structure Analysis of Aurivillius Phases Pb1‐xBi4‐+Ti1‐xMnxO15

Synthesis Pb_1‐xBi_4+xTi_4‐xMn_xO₁₅ compounds (0 ≤ × ≤ 1) were carried out by molten salts method using eutectic mixture of Na₂SO₄/K₂SO₄ salts (1:1 molar ratio) as the flux. The samples were characterized by X‐ray powder diffraction and refined by Le Bail method using Rietica program. The refinement results revealed that the compounds with the composition 0 ≤ x ≤ 0.6 formed Aurivillius phase with the space group A2₁am while the other composition (x ≥ 0.8) showed another phase beside A2₁am. The ratio b/a of the lattices constants for all the samples are larger than 1 indicating the direction of the orthorhombic along the b axis of their cells. The lattice parameters and volume of the unit cells decrease as the Mn content increasing from x = 0 to 0.6, for x ≥ 0.8 a second phase were observed. The morphologies of Pb_1‐xBi_4+xTi_4‐xMn_xO₁₅ samples were observed by SEM and show plate‐like aggregate crystals, typical of layered compounds belonging to the Aurivillius phase.     

Synthesis and electrochemical properties of spinel LiMn2O4 prepared by the rheological phase method

Pure-phase and well-crystallized spinel LiMn₂O₄ powders were successfully synthesized by a simple rheological phase method. The thermal behavior and structure properties of the powders prepared by the rheological phase method compared with the solid-state reaction were investigated by thermogravimetry, powder X-ray diffraction , scanning electron microscopy and transmission electron microscopy. According to the results of the electrochemical tests, it is obvious that the sample resulting from the rheological phase method shows higher discharge capacity and better cycling stability than one formed in the solid-state reaction. The cyclic voltammogram and columbic efficiency curves also confirm that the product by the rheological phase method has a good cycling performance due to its fine cubic spinel structure and morphology.     

Copper-cerium oxide catalysts prepared by the Pechini method for CO removal from hydrogen-containing mixtures

A series of copper-cerium oxide catalysts was prepared by the Pechini method, and their physicochemical and catalytic properties in CO oxidation in hydrogen-containing gas mixtures were studied. The method chosen for catalyst preparation yields finely dispersed copper and cerium oxides in the catalyst.     

Aurivillius phases of PbBi4Ti4O15 doped with Mn synthesized by molten salt technique: Structure, dielectric, and magnetic properties

Doping of manganese (Mn³⁺/Mn⁴⁺) into the Aurivillius phase Pb_1−xBi_4+xTi_4−xMn_xO₁₅ was carried out using the molten salt technique for various Mn concentrations (x=0, 0.2, 0.4, 0.6, 0.8, and 1). Single phase samples could be obtained in the composition range with x up to 0.6 as confirmed by X-ray and neutron diffraction analysis. Dielectric measurements show a peak at 801, 803, 813 and 850 K for samples with x=0, 0.2, 0.4, and 0.6, respectively, related to the ferroelectric transition temperature (T_c). The main contribution of the in-plane polarization for x≤0.2 which was calculated from the atomic positions obtained by the structure analysis is the dipole moment in the Ti(1)O₆ layer; however, for x≥0.4 the polarization originates from the dipole moment in the Ti(2)O₆ layer. Mn doping in the Pb_1−xBi_4+xTi_4−xMn_xO₁₅ does not show any long range magnetic ordering.     

CaWO4-YNbO4固溶体的Pechini溶胶-凝胶法合成及其发光性能

利用Pechini溶胶-凝胶法成功地合成了一系列CaWO4 - YNbO4固溶体Ca1-xYxW1-xNbxO4(1),其结构和性能经XRD,IR,SEM,PL等表征.结果表明,在NbO43-的掺杂量(x)为25％,于800℃焙烧2h的条件下合成的1最佳.W-O电荷迁移跃迁随着x的增加发生明显的蓝移,其荧光强度降低.     

Aurivillius Phases in the Bi4Ti3O12/BiFeO3 System: Thermal Behaviour and Crystal Structure

Four compounds of the Bi₄Ti₃O₁₂/BiFeO₃ system with the formula Bi₂Bi_n?1(Ti,Fe)_nO_3n+3, n = 3, 4, 4.5 and 6 were studied using high‐temperature X‐ray powder diffraction and differential thermoanalysis methods. The crystal structure of the n = 6 phase was refined by the Rietveld method. An unusual behaviour of thermal expansion attributed to an orthorhombic‐to‐tetragonal transformation was revealed. For all the compounds, the lattice parameter c vs temperature T dependence has three regions in the range of T = 20 –750 °C interpreted as (1) expansion of the initial orthorhombic phase, (2) a pronounced structure reconstruction to the tetragonal phase, (3) an expansion of the tetragonal phase. The crystal structure of Bi₇Ti₃Fe₃O₂₁ based on 6‐layer‐perovskite blocks is proposed from X‐ray powder diffraction data. The Rietveld refinement of the structure in the orthorhombic space group F2mm with lattice parameters a = 5.4699(3), b = 5.4924(3), c = 57.551(3) Å (R_p = 9.4, R_wp = 11.9, R_exp = 4.7, R_B = 4.4 %) shows that a distorted 6‐layer model fits the data of Bi₇Ti₃Fe₃O₂₁.     

Notable enlargement of remnant polarization for fatigue-free SrBi4Ti4O15 thin films by La-substitution

La-doped SrBi₄Ti₄O₁₅, SrBi_4–x La _x Ti₄O₁₅ (SBLT-x, x = 0.00, 0.10 and 0.25), thin films have been successfully prepared by the sol–gel method. Structures, surface morphology and ferroelectric properties were investigated. Compared with undoped SBTi, SBLT-0.10 shows a notable larger remnant polarization (2P _r = 46 μC/cm²). Meanwhile, the SBLT-0.10 film shows little change of P _nv and −P _nv up to 4.4 × 10¹⁰ switching cycles, suggesting an excellent fatigue-endurance characteristics.     

Preparation and electrochemical properties of Co3O4-coated layered manganese oxide by a novel coating method

Potassium type birnessite (K-bir) was synthesized by O₂ oxidizing Mn²⁺ in aqueous solution of KOH. Co₃O₄-coated K-bir (Co-K-bir) was prepared by employing a novel coating method, in which the remaining OH⁻ ions on the particle surface of the as-precipitated K-bir reacted with Co²⁺ ions in aqueous solution, forming CoOOH coverage; the coating layer of CoOOH was subsequently annealed at 300 °C to transform into Co₃O₄. All the K-bir and Co-K-birs were investigated by scanning electron microscopy, transmission electron microscopy, inductive coupled plasma–atomic emission spectroscopy, Brunauer–Emmett–Teller specific area, and laser particle size analyzing techniques. Their electrochemical properties were also studied by discharging–charging at constant current. The results show that the covering layers of Co₃O₄ are incompact, and their average thickness are about 0.65–0.78 μm. Compared to the as-prepared and the annealed K-bir, the Co₃O₄-coated samples have higher initial discharge capacities and show distinctly improved cycleability performance.     

Synthesis of MgCo2O4-coated Li4Ti5O12 composite anodes using co-precipitation method for lithium-ion batteries

Journal of Solid State Electrochemistry - In the present work, we report synthesis of MgCo2O4 (MCO)/Li4Ti5O12 (LTO) composites for Li-ion battery anodes by a co-precipitation method. The objective...     

Synthesis and electrochemical properties of chemically substituted LiMn2O4 prepared by a solution-based gel method

Lithium manganese oxide, LiMn(2)O(4), and its substituted samples LiM(0.05)Mn(1.95)O(4) (M=Al, Co, and Zn) were first prepared by a cost-saving and effective new solution-based gel method using a mixture of acetate and ethanol as the chelating agent. The physical properties of the synthesized samples were investigated by thermogravimetry/differential thermal analysis, X-ray diffraction, and scanning electronic microscopy. The as-prepared powders were used as positive materials for a lithium-ion battery, whose charge/discharge properties and cycle performance were examined. The results revealed that all the substituted samples had better cycle performance than pure LiMn(2)O(4). Among these synthesized materials, the LiCo(0.05)Mn(1.95)O(4) sample had the best cycle performance. After 30 cycles, its capacity loss was only 3%. Therefore, cyclic voltammetry and electrochemical impedance spectroscopy were employed to characterize the reactions of Li ion insertion into and extraction from LiCo(0.05)Mn(1.95)O(4) electrodes.