Tartaric Acid-assisted Sol Gel Research Articles

Aqueous sol–gel synthesis, thermoanalytical, structural and vibrational studies of lithium aluminium molybdate (LiAlMo2O8)

Aqueous tartaric acid-assisted sol–gel preparation technique was successfully applied to synthesise lithium aluminium molybdate with the initial composition of LiAl(MoO4)2. From the results of the thermal analysis and Xray diffraction measurement, the effect of tartaric acid as a ligand on the formation of homogeneous gel precursor was discussed. Besides, X-ray diffraction also revealed the crystallisation of the final LiAlMo2O8 ceramic below the temperature of 400°C. It was found that the initial composition of obtained ceramic significantly affected the formation of the impurity phase defined as AlMo2O12. The Rietveld refinement of the crystalline samples showed the tendency of crystallites growing with the increase of heat-treatment temperature. Similar trends of particle growing were also observed in the images of scanning electron microscopy (SEM) for the corresponding samples heat-treated at different temperatures. Finally, the Fourier-transform infrared spectroscopy (FT-IR) revealed the effect of both the surface morphology and the crystallite size on the intensity of characteristic vibration of the corresponding chemical bonds.

Investigating the effect of Pr doping BiFeO3 on the microwave absorption and magnetic properties

Bi1-xPrxFeO3 material with perovskite structure was prepared using organic tartaric acid-assisted sol–gel self-propagating combustion method to obtain high-efficiency microwave absorption materials. The influence of the introduction of Pr on dielectric properties and permeability was further studied. After 15% Pr introduced, the lowest reflection absorption loss reaches –32.34 dB, but the absorption bandwidth is only 2.25 GHz. When Pr is 5%, the lowest reflection absorption loss value of −27.31 dB is obtained, and the effective bandwidth which below −10 dB is 3.41 GHz. The structural changes in the process of Pr replacing Bi were analyzed to explore the properties of BPFO perovskite. The influence of strong interaction force, residual magnetization, and natural resonance of ceramic nanoparticles on microwave absorption performance was explored. This work supplies a reliable candidate material for making up electromagnetic attenuation ceramic materials with excellent properties.

Synthesis and characterization of samarium substituted bismuth ferrites nanoparticles

Bi1-xSmxFeO3 (x = 0.00, 0.05, 0.15) nanoparticles have been prepared through tartaric acid assisted sol–gel method. The X-ray diffractogram was used to confirm the phase formation and it revealed the single-phase formation with R3c space group. SEM analysis revealed that the particle size decreased with increasing Sm concentration. The crystallite size was observed to be in the range of 30 nm. M-H study depicted an increase in magnetization with increasing samarium concentration. Electron paramagnetic resonance (EPR) of magnetization studies was found to be in agreement with results of the vibrating sample magnetometer (VSM) magnetization studies.

Peculiarities of charge carrier relaxation in grain boundary of gadolinium-doped ceria ceramics

Two different gadolinium-doped ceria ceramics are prepared from two different powders, one commercially available synthesised by solid state reaction and another produced by tartaric acid assisted sol–gel synthesis. The specimens have a different microstructure, while the XRD patterns of powders showed a pure cubic fluorite structure without any impurity phase. The electrical properties are studied at frequencies up to 10 GHz by combining broadband 2-electrode and 4-electrode impedance spectroscopy methods. Primary electrical measurements showed that the values of grain conductivity and its activation energies for both ceramics were nearly the same. However, due to different contributions of the grain boundary mediums, total conductivities and their activation energies are found to be considerably different. The advantage of the 4-electrode method allowed us to measure the pure electrical response of grain boundaries, bypassing any interferences caused by interfacial impedance. By using these data, the temperature behaviour of distribution of relaxation times in the grain boundary is studied. A broadening of this distribution with increasing temperature is found for both specimens, contrary to a previously observed phenomenon in the grain of oxygen ion conductive ceramics and single crystals. It is shown that, supposing individual relaxation times behave according to the Arrhenius law, both activation energy and pre-exponential factor must be distributed.

Co-substitution induced structural transition with enhanced magnetic and electrical properties of multiferroic BiFeO3 nanoparticles

Polycrystalline Bi1−xTbxFe1−xCoxO3 (for x = 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by tartaric acid assisted sol–gel route. The quantitative crystallographic phase analysis of XRD pattern demonstrates the subsequent structural phase transition from rhombohedral (R3c) to cubic (Pm $$\bar {3}$$ m) with the intermediate orthogonal (Pbnm) and orthogonal (Pnma) phase with the gradual increase in concentration of co-substituents. Raman spectroscopic analysis emphasizes that all the co-substituted samples has undergone structural phase transitions which are in good agreement with the results of Rietveld analysis. X-ray photoelectron spectroscopy (XPS) have confirmed that Fe exists predominantly in +3 state in the co-substituted sample. The enhancement in the room temperature magnetic behavior of the sample can be attributed to the co-substitution induced suppression of spatially modulated spiral spin structure of BiFeO3. All the samples exhibit dielectric anomaly at the vicinity of Neel temperature (TN) signifies the change in magnetic ordering. Moreover, all the co-substituted samples have been witnessed with reduced leakage current and improved ferroelectric behaviour, which is the desirable characteristics for multifunctional device applications of multiferroics.

Preparation of spinel LiNi0.5Mn1.5O4 and Cr-doped LiNi0.5Mn1.5O4 cathode materials by tartaric acid assisted sol–gel method

In this article, LiNi0.5Mn1.5O4 and LiNi0.4Cr0.15Mn1.45O4 are prepared by the tartaric acid-assisted sol–gel method. It can be found that Cr doping not only can suppress the formation of impurity phase in the final product but also can increase the cation ordering in the spinel structure. Morphology observation reveals that the introduction of tartaric acid in the preparation leads to a controlled cubic morphology and a narrow particle size distribution. It is clear that both LiNi0.5Mn1.5O4 and LiNi0.4Cr0.15Mn1.45O4 consist of octahedrons with the particle size ranging from 0.5 to 1.5μm. Charge/discharge tests show that LiNi0.4Cr0.15Mn1.45O4 can deliver a higher initial discharge capacity (143.9mAhg−1) than that of undoped LiNi0.5Mn1.5O4 (136.6mAhg−1). After 40 cycles, the reversible discharge capacity of LiNi0.4Cr0.15Mn1.45O4 can be still maintained at 139.7mAhg−1. For comparison, LiNi0.5Mn1.5O4 only shows a reversible discharge capacity of 127.7mAhg−1. It suggests that Cr substitution for Ni and Mn in the spinel structure can effectively improve the electrochemical performance of LiNi0.5Mn1.5O4.

Synthesis and characterization of GdVO4 nanostructures by a tartaric acid-assisted sol–gel method

GdVO4 nanoparticles were prepared by a sol–gel method employing tartaric acid as a chelating agent. Effects of calcination temperature and mole ratio of total metal ions to tartaric acid on the products were investigated. The products, characterized by XRD, FESEM and TEM, were tetragonal GdVO4 nanoparticles with diameters of about 20–30nm. TG and DSC data showed weight loss and phase formation due to evaporation and decomposition processes. FTIR presented the stretching band of VO43− tetrahedrons and Raman analysis revealed the vibrational modes of the GdVO4.

Modifications in the rhombohedral degree of distortion and magnetic properties of Ba-doped BiFeO3 as a function of synthesis methodology

We present an analysis of crystallographic symmetry and the origin of the pseudo-cubic character of doped BiFeO3. Specifically, barium-doped bismuth ferrite, Bi1−xBaxFeO3 (x = 0.05, 0.075, 0.1, 0.125), perovskite-type nanoparticles have been synthesized by implementing five modifications to the sol–gel technique (citric acid-assisted sol–gel method, ethylene glycol method, tartaric acid-assisted sol–gel method, polyvinyl alcohol–ethylene glycol method, and EDTA complexing sol–gel method) and their final pseudo-cubic character is discussed. The effect of the carboxylic groups and hydroxyl groups during synthesis is critical to obtain single phase BBFO. Fourier transform infrared spectroscopy and thermogravimetric analysis is used to study the decomposition and thermal behavior of the precursors and their relation to the final nanoparticle characteristics. X-ray diffraction analysis shows a single phase with symmetry changes for four of the five synthesis methodologies employed. Only the EDTA complexing sol–gel method, where EDTA is used as dissolver and chelating agent, is not satisfactory in all concentration ranges. Rietveld results suggest that the degree of distortion of the rhombohedral symmetry in the crystallized BiFeO3 powders decreases 12% as a result of progressive substitution of Bi3+ by Ba2+ and that there is no shift from rhombohedral to tetragonal symmetry. Magnetization properties of samples with a low-distortion rhombohedral structure show higher magnetic saturation and remanent magnetization than samples with high-distortion rhombohedral structure.

Enhanced electrochemical performance of carbon-coated Li2MnSiO4 nanoparticles synthesized by tartaric acid-assisted sol–gel process

A tartaric acid-assisted sol–gel process was used to synthesize Li2MnSiO4 (SG-LMS) nanopowders with orthorhombic structures (Pmn21 space group). The Li-active SG-LMS nanoparticles were fully surrounded by a conducting amorphous carbon layer/matrix that was formed by carbonization of the tartaric acid during post-annealing of the dry gel. The SG-LMS electrode exhibited higher specific capacity and superior cycle retention as compared to the LMS electrode prepared by a conventional solid-state reaction. Such high electrochemical performance originated from the presence of a high-purity phase, a large surface area, and an efficient electron transport path facilitated by the conductive carbon coating of the SG-LMS electrode.

Tartaric acid assisted synthesis of Li2FeSiO4/C: Effect of carbon content on the electrochemical performance of Li2FeSiO4/C for lithium ion batteries

Li2FeSiO4/C composites were successfully prepared by tartaric acid assisted sol–gel route. Tartaric acid was used as both the chelating agent and carbon source. Effects of carbon content on the physical and electrochemical performances of the samples were studied in detail. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge and AC impedance spectroscopy, respectively. The particle size of Li2FeSiO4/C decreases with increasing content of carbon; however higher content of carbon will lead to poorer crystallinity and more impurities. When the carbon content is 4.0wt.%, the Li2FeSiO4/C sample has the largest exchange current density (i°=0.110mAcm−2) and highest diffusion coefficient of lithium ion (DLi+=1.01E−12cm2s−1). Thus, Li2FeSiO4/C with 4.0wt.% carbon has the best electrochemical properties, in terms of discharge capacity and cycling stability. It exhibits an initial discharge capacity of 119.7mAhg−1 at C/16 rate at room temperature. When cycled at C/10 rate, the Li2FeSiO4/C sample with 4.0wt.% carbon delivers an initial discharge capacity of 96.6mAhg−1, and 98.6% of the initial discharge capacity remained after 25 cycles.

Sol–gel synthesis, characterization and luminescent properties of Tb3+ doped MLa2O4 (M=Sr or Ba) nanophosphors

Abstract Tb3+ doped SrLa2O4 and BaLa2O4 nanophosphors were successfully synthesized via tartaric acid assisted sol–gel method and their luminescent properties were investigated. The crystal structure and morphology of SrLa2O4:Tb3+ and BaLa2O4:Tb3+ was studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Thermal decomposition behavior of the dried gels was investigated by thermogravimetry (TG) and differential thermal analysis (TGA). Photoluminescence (PL) behaviors of these nanophosphors were checked by the excitation and emission spectra. These SrLa2O4 and BaLa2O4 nanophosphors displayed green color under a UV source due to characteristic transition of Tb3+ from 5D4 → 7F5 at 544 nm. The dependence of photoluminescence intensity on Tb3+ ion concentration, tartaric acid concentration and annealing temperature were also studied in detail. In addition, the optimum doping concentration and time-resolved luminescence spectroscopy were also investigated.

Synthesis and electrochemical performance of Li1+xV3O8 as cathode material prepared by citric acid and tartaric acid assisted sol–gel processes

Lithium-ion battery cathode material Li1+xV3O8 is synthesized by a citric acid/tartaric acid assisted sol–gel method and sintered at 350 °C, 450 °C and 550 °C for 3 h for the formation of Li1+xV3O8 phase. The synthesized samples were fully characterized by FTIR, TG/DTA, XRD, SEM, EIS and charge–discharge tests. Li1+xV3O8 material synthesized by tartaric acid assisted route and sintered at 450 °C for 3 h shows best electro-chemical performance. It shows a high initial capacity of 249 mAh g−1 and still reserves a discharge capacity of 260 mAh g−1 after 50 cycles. Moreover, in the case of tartaric assisted products, no capacity decadence is observed in 50 cycles. XRD together with TG/DTA measurements reveal that compared with citric acid assisted products, the adoption of tartaric acid as chelating agent effectively lowers the crystallization temperature of amorphous Li1+xV3O8. Therefore, precursors obtained by tartaric acid route calcinated at 450 °C for 3 h exhibit lower crystallinity and smaller grain size, which contributes to the better electrochemical performance of the cathode electrodes. From EIS measurements, the bulk resistance is reduced, which favors the intercalation and de-intercalation of lithium ions while cycling.

Synthesis, spectral character, electrochemical performance and in situ structure studies of Li1+xV3O8 cathode material prepared by tartaric acid assisted sol–gel process

Lithium-ion battery cathode material Li1+xV3O8 was synthesized by a tartaric acid assisted sol–gel method and thermally treated at 350°C, 450°C and 550°C for 3h for the formation of Li1+xV3O8 phase. The synthesized samples were fully characterized by FTIR, TG/DTA, XRD and charge–discharge tests. Li1+xV3O8 material synthesized by tartaric acid assisted route, followed by heat treatment at 450°C for 3h shows best electro-chemical performance. It shows a high initial capacity of 249mAhg−1 and still reserves a discharge capacity of 260mAhg−1 after 50 cycles. Moreover, for all tartaric assisted products, no capacity decadence is observed in 50 cycles. The in situ X-ray measurements reveal a two-phase transition mechanism in the lithium intercalation/deintercalation process. During lithium extraction, the structure of the delithiated compound changes from Li4V3O8 (x>3.1) to the original LiV3O8 phase (x<1.4) via the coexistence state of these two phases (1.4<x<3.2). An obvious contraction, especially at Li(3)–Li(4) transition, along a axis and a slight expansion along b axis are also observed.

Large-scale synthesis of Li1.15V3O8 nanobelts and their lithium storage behavior studied by in situ X-ray diffraction

Li1.15V3O8 nanobelts with length 3 μm, width 200 nm and 20–50 nm in thickness are prepared on a large scale by a tartaric acid-assisted sol–gel technique. They show greater reversibility of the lithium ion insertion/extraction reaction than those synthesized without the addition of tartaric acid. After twenty cycles, the reversible lithium storage capacities of Li1.15V3O8 prepared from tartaric acid assisted and free techniques are 231.0 and 194.5 mAh/g at a current density of 30 mA g−1, respectively. Cycled at 20 mA g−1 in 1.5–4.1 V, Li1.15V3O8 nanobelts can deliver discharge and charge capacities of 297.0 and 298.4 mAh/g, respectively. Increasing the charge/discharge current density to 2400 mA g−1, the lithiation and delithiation capacities of Li1.15V3O8 nanobelts can be mantianed at 184.2 and 184.2 mAh/g, respectively. In situXRD observation reveals that the host structure of Li1.15V3O8 nanobelts will not be destroyed with a discharge process to 0.0 V at 20 mA g−1 or a short circuit for 24 h. Over-lithiation can induce the formation of an inactive compound, leading to poor electrochemical properties of Li1.15V3O8 nanobelts. The first lithiation/delithiation process in 0.0–4.1 V or 1.5–4.1 V is a reversible reaction at a current density of 60 mA g−1, and is composed of reversible single-phase structural evolutions in a high voltage region and two-phase structural transitions in a low voltage region. The electrochemical properties of Li1.15V3O8 nanobelts are poorer at the 10th cycle in 0.0–4.1 V than that obtained in 1.5–4.1 V. In situXRD results indicate that the breakdown of two-phase transition in a low voltage region is the main factor for poor cycleability. Besides, a delay of structural evolution and asymmetry lithiation/delithiation process can be observed at high rates, which may also be responsible for the deterioration of cycleability of Li1.15V3O8 nanobelts.

Photoluminescence of Bismuth Germanate Phosphors with a Silica-shell Structure

Abstract An intense bluish-white emitting phosphor Bi 4 Ge 3 O 12 (BGO) was synthesized by tartaric acid-assisted solgel method and covered with a SiO 2 nanolayer by the sol-gel method. The cubic crystal structure of BGO was confirmed by X-ray diffraction. Transmission electron microscopy analysis revealed the particle size to be in the range of 6-20 nm. Under excitation with 4.3 eV photons the BGO powders showed a PL contribution centered at 2.43 eV that corresponds to the typical BGO luminescence associated with 3 P 1 a 1 S0 of Bi 3+ electron transitions. Radioluminescence measurements showed the predominant emission centered at 2.43 eV due to the intra-ionic Bi3+ transitions. The PL emission of the silica coated BGO nanoparticles presented a luminescence enhancement of more than 200% compared with the uncoated nanoparticles. This enhancement in photoluminescence is proposed to be related to the reflectivity (refractive index) between air-silica-BGO layers.

Tartaric acid-assisted sol–gel synthesis of LiNi 0.5Co 0.5−xTi xO 2 (0 ⩽ x ⩽ 0.5) as cathode materials for lithium-ion batteries

A series of LiNi 0.5Co 0.5− x Ti x O 2 (0 ⩽ x ⩽ 0.5) are prepared by a tartaric acid-assisted sol–gel technique. The phase formation process is observed by TG–DTA. It is found that the target product appears at a temperature higher than 400 °C and completes to phase formation at 700 °C. The crystal structure and morphology are characterized by XRD, SEM and Raman spectroscopy. XRD patterns show that the as-prepared sample transforms from hexagonal structure into cubic structure with the increase of Ti content in LiNi 0.5Co 0.5− x Ti x O 2. Raman spectra also demonstrate the successive substitution of Ti for Co in the structure with band blue-shift phenomenon. SEM images confirm that the as-prepared sample exhibits narrow and regular particles with the size between 0.5 and 1.5 μm. The apparent particle size of sample starts to decrease with x ⩽ 0.1, and the gradually increases by introducing Ti dopant with higher content ( x ⩾ 0.15). The electrochemical behavior of the sample displays different characteristics after Ti substitution. It is found that the initial working potential increases with the increase of Ti doping content. As a result, the initial lithium storage capacity for trace Ti-doped sample is higher than that delivered by the pristine one. The decrease of reversible capacity for high degree Ti-doped sample is ascribed to the electrochemical inactivity of the cubic compound in the sample. Therefore, trace Ti doping is beneficial to achieve promising cathode material for lithium-ion batteries.

Porous Li 2FeSiO 4/C nanocomposite as the cathode material of lithium-ion batteries

In this paper, we report on the facile preparation of porous Li 2FeSiO 4/C nanocomposites by tartaric acid-assisted sol–gel method and their electrochemical properties as the cathode materials of Li-ion batteries. The structure, morphology, and texture of the as-prepared samples are characterized by means of XRD, Raman, SEM, TEM/HRTEM, and N 2 adsorption/desorption techniques. The results show that the porous Li 2FeSiO 4/C nanocomposites are consisted of nanoparticles, which have been coated with in situ carbon on the surface. The electrochemical properties of the as-prepared Li 2FeSiO 4/C nanocomposites have been investigated using galvanostatic charge/discharge and cyclic voltammograms. It is found that porous Li 2FeSiO 4/C nanocomposite with 8.06 wt% carbon shows a high capacity of 176.8 mAh g −1 at 0.5 C in the first cycle and a reversible capacity of 132.1 mAh g −1 at 1 C (1 C = 160 mA g −1) in the 50th cycle. This high capacity indicates that more than one electron reaction may be occurred. These results illustrate that the porous Li 2FeSiO 4/C nanocomposite with 8.06 wt% carbon is potential in the application of high-rate cathode material of Li-ion batteries.

Synthesis and electrochemical properties of porous LiV 3O 8 as cathode materials for lithium-ion batteries

In this paper, we report on the synthesis of porous LiV 3O 8 by using a tartaric acid-assisted sol–gel process and their enhanced electrochemical properties for reversible lithium storage. The crystal structure, morphology and pore texture of the as-synthesized samples are characterized by means of XRD, SEM, TEM/HRTEM and N 2 adsorption/desorption measurements. The results show that the tartaric acid plays a pore-making function and the calcination temperature is an important influential factor to the pore texture. In particular, the porous LiV 3O 8 calcined at 300 °C (LiV 3O 8-300) exhibits hierarchical porous structure with high surface area of 152.4 m 2 g −1. The electrochemical performance of the as-prepared porous LiV 3O 8 as cathode materials for lithium ion batteries is investigated by galvanostatic charge–discharge cycling and electrochemical impedance spectroscopy. The porous LiV 3O 8-300 displays a maximum discharge capacity of 320 mAh g −1 and remains 96.3% of its initial discharge capacity after 50 charge/discharge cycles at the current density of 40 mA g −1 due to the enhanced charge transfer kinetics with a low apparent activity energy of 35.2 kJ mol −1, suggesting its promising application as the cathode material of Li-ion batteries.

Magnetic and optical properties of multiferroic bismuth ferrite nanoparticles by tartaric acid-assisted sol–gel strategy

Pure BiFeO 3 nanoparticles have been successfully synthesized through the tartaric acid-assisted sol–gel method at relatively low temperature. The as-prepared nanoparticles were characterized by a variety of techniques. The success in preparing pure BiFeO 3 may be attributed to the formation of heterometallic polynuclear complexes in the tartaric acid system. The ferroelectric phase transition ( T C = 851 °C) was determined, revealing the ferroelectric nature of the as-prepared BiFeO 3 nanoparticles. The result of magnetic measurement indicates the weak ferromagnetic order of BiFeO 3 nanoparticles at room temperature, which may be ascribed to the size confinement effect. The observed strong absorption in the UV region will enable BiFeO 3 nanoparticles to be potentially used as promising photocatalytic decomposition material.

Tartaric acid-assisted sol–gel synthesis of Y2O3:Eu3+ nanoparticles

Abstract In the present work, Y 2 O 3 :Eu 3+ nanoparticles have been synthesized by tartaric acid-assisted sol–gel method. The advantages of low temperature solution-based process have been exploited to produce Y 2 O 3 :Eu 3+ nanoparticles. Synthesis conditions such as calcination temperature and tartaric acid concentrations are varied in order to determine the exact optimal conditions for synthesizing nanoparticles with superior optical properties. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies have been carried out to understand surface morphological features and the particle size. Crystal structure of the nanoparticles has been investigated by X-ray diffraction (XRD) technique. Nanoparticles have average crystallite size from 20 to 45 nm. The incorporation of Eu 3+ activator in these nanoparticles has been checked by luminescence characteristics. These nanoparticles have displayed red color under a UV source. The main emission peak at 612 nm corresponds to the hypersensitive transition between 5 D 0 and 7 F 2 level of Eu 3+ ions. IR analysis has also been performed for the analysis of the nanoparticles.