Pechini Sol Gel Research Articles

Effect of 20% Cr-doping on structural and electrical properties of La0.67Ca0.33MnO3 perovskite

Structural and electrical properties of La0.67Ca0.33Mn1-xCrxO3 (x = 0 and 0.2) manganites are studied in this work. The samples were prepared using Pechini sol-gel method at 1173 K. Rietveld analysis of X-ray diffraction (XRD) patterns shows the formation of pure crystalline phase with orthorhombic Pnma structure with a decrease of the unit cell volume and crystalline domain size when increasing Cr-content. Electrical properties of the samples have been investigated using complex impedance analysis in 180–320 K temperature range with varying frequency between 40 and 106 Hz. For both samples, frequency dependence of imaginary part of impedance (Z″) shows the existence of relaxation phenomenon. The impedance study using Nyquist representation revealed the appearance of semicircle arcs and an equivalent circuit of the type of R1 + (R2//ZCPE) has been proposed to explain the impedance results. The conductance curves were analyzed by Jonscher power law and the deduced activation energy values are close to those calculated from relaxation time indicating that relaxation process and conductivity have the same origin.

Pechini Synthesis of LiFeBO3/C and Application As Cathode Material in Lithium Ion Batteries

The development of new cathode materials with high capacity, good stability, and high safety is important for the future improvement of lithium batteries. While most cathodes in commercial cells uses layered oxides, materials containing polyanion groups such as phosphate (PO4), silicates (SiO4), and borates (BO3) have generated interest because of the inherent stability of the polyanion group against oxygen lost [1-4]. There is a need for cathode materials working at higher output voltages with higher practical capacities. Borates could be good alternative to phosphates by having the lower weight BO3 -3 group instead of PO4 -3, but keeping the advantage of the linking anion group giving higher operating voltage and enhanced structural stability [5]. In this research work the synthesis of LiFeBO3/C composite was achieved using Pechini sol-gel method. In order to determine the influence of the carbon content in the formation of composite LiFeBO3/C, different molar ratio compositions of iron precursor and citric acid (Fe:CA) such as 1:0.1, 1:0.5, 1:1 and 1:2 were prepared. Starting precursors were salts of LiNO3, Fe(NO3)3·9H2O, H3BO3 and citric acid/ethylene glycol were used for polyesterification reaction. Aqueous solutions containing appropriate amounts of salts were poured into a mixture of citric acid and ethylene glycol solution. Mixture was then heat treated under reflux at 80°C until gel formation. In order to determine heating temperatures for Pechini sol-gel samples, simultaneous thermal analysis TGA-DTA was carried out. Fresh samples were preheated at 300°C under air to eliminate volatile matter. Resulting powders were ground and formed into pellets for reaction between 550 to 650°C under nitrogen atmosphere. Morphological and microstructural characterization were carried out with field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), textural analysis by N2 physisorption with BET method; and crystalline phases were determined with X-ray powder diffraction (XRD); the application of materials as cathodes in lithium ion batteries was evaluated through electrochemical charge discharge experiments. Electrodes were prepared using a mixture of each synthesized materials, conductive carbon and PVDF binder. CR2032 coin cells were assembled inside a glove box under Ar atmosphere, using LiPF6electrolyte and Li° as anode. Experiments were performed using a MacPile II by Biologic. Thermal analysis of sol-gel reaction products exhibited an exothermic even between 550 and 600°C attributed to the crystallization of the borates. It has been found that the variation of iron:citric acid (Fe:CA) molar ratio yielded different particle size and crystallinity of the composite. The 1:1 and 1:2 molar ratio compositions of Fe:CA, and temperatures between 550-650°C for 10h were the experimental conditions that produced a single phase material with improved characteristics such as small particle size, crystallinity and porosity. Mesoporous materials were obtained, with specific surface areas of 4.96 and 36.06 m2 g-1 for composites with Fe:CA molar ratio of 1:1 (LFB1) and 1:2 (LFB2) respectively. Morphology of LFB1 samples correspond to particles with irregular shapes and size about 187.8-361.7 nm, in the other hand samples of LFB2 contain primary spherical particles forming clusters, with particle sizes between 42 and 78 nm, this can be attributed to the effect of residual carbon within samples since this inhibits particle grown and also allows contact among particles, improving electrical conductivity. LFB1 composite tested in lithium cell present a specific capacity of 202 mAhg-1 during the first 10th discharge cycles with columbic efficiency of 95 %. LFB2 showed a specific capacity of 213 mAh g-1 during discharge, corresponding to 97% of theoretic capacity, using current densities of 5 and 10 mA g-1. A specific capacity of 198 mAh g-1 was obtained during discharge, corresponding to 90% of theoretic capacity, using current density of 50 mA g-1. These results seem favorable for future application of the material in lithium ion batteries. Keywords: Lithium-ion batteries; cathode material; Pechini sol-gel; borates; LiFeBO3

Why Is Li2MnSiO4 Unstable in Li-Ion Battery Cell? Structural Studies at Different Stages of Electrochemical Reaction

Application of orthosilicates Li2MSiO4 (M=Fe, Mn, Co, Ni) compounds as insertion materials for LIBs was firstly proposed by Prof. Goodenough [1]. The materials mainly crystallize in orthorhombic system of Pmn21 space group in olivine structure [2-4]. The Li2MSiO4 olivine structure may be described as wavy layers of [SiMO4]∞ on ac axis plane and connected along b axis by LiO4 tetrahedra [2]. Within the layers every SiO4 tetrahedron shares its corner with four next MO4 tetrahedra. Lithium ions occupy the tetrahedral sites (LiO4) between two layers and share 3 and 1 oxygen atoms with the layers. In fact, diffusion of lithium ions in this structure is possible only through the canals formed by LiO4 tetrahedra. Li2MSiO4 silicates reveal a possibility of reversible insertion of two lithium ions per molecule, which leads to exchange of two electrons by transition metal. As a results the silicates reveal high theoretical capacity, up to 330 mA/g for Li2MnSiO4 (LMS). LMS, which works at potentials 4.2 and ~4.5 V for first and second redox reactions respectively, seems to be the most useful from all of dilithiumorthosilicates family compounds. The main disadvantage of LMS is its extremely low electrical conductivity [2,5] and structural instability [7-11]. While the conductivity issues can be fixed by the preparation of nanograined material and its modification by carbon coating, similarly to the procedures applied in case of LiFePO4, the reasons of structural instability of LMS are not entirely known. There is a number of reports showing that Li2MnSiO4 cathode material undergoes amorphization in the first few charging/discharging cycles but there is no comprehensive explanation of this phenomenon. The degradation of crystalline structure can be caused by Jahn–Taller distortion associated with changes in lattice parameters during Mn3+→Mn4+ transition [8]. Another explanation may be the occurrence of secondary reactions between electrolyte and delithated forms of lithium manganese silicate (LiMnSiO4 and MnSiO4). The aforementioned structural changes of the material entail variations in electrochemical properties of Li2MnSiO4[9]. The goal of this studies is to examine structural instability of Li2MnSiO4which occurs in first electrochemical charging/discharging cycle via microscopic analysis of individual grains at different stages of electrochemical reaction. The Li2MnSiO4material was prepared using Pechini's sol–gel method which was previously reported by our group [9-11]. The structural changes in the material was studied using in-situ X-Ray diffraction as well as ex-situ transmission electron microscopy. To determine degradation mechanism of Li2MnSiO4 and C/Li2MnSiO4 in working Li-ion cell two different aspects of LMS performance were analyzed. Firstly corrosive properties of liquid electrolytes were taken under consideration. Solubility of manganese from LMS and C/LMS samples (occurring during electrochemical reaction) in LiPF6solution in EC:DMC (1:1) was studied. On the other hand using in-situ XRD and ex-situ TEM analysis in different SOC (in initial cycle in 1.5-4.8V potential range) the process of amorphization of crystalline LMS was examined. ACKNOWLEDGMENT This work is supported by National Science Centre, Poland under research grant no. 2014/13/B/ST5/04531. REFERENCES Padhi A.K., Nanjundaswamy K.S., Goodenough J.B. J. Electrochem. Society 144 (1997) 1188-1194.M.E. Arroyo-de Dompablo, M. Armand, J.M. Tarascon, U. Amator, Electrochem. Commun. 8 (2006) 1292–1298.A. Nyten, A. Abouimrane, M. Armand, T. Gustafsson, J.O. Thomas, Electrochem. Commun. 7 (2005) 156–160.Z.L. Gong, Y.X. Li, Y. Yang, J. Power Sources 174 (2007) 524–527.A. Kokalj, R. Dominko, G. Mali, A. Meden, M. Gaberscek, J. Jamnik, Chem. Mater. 19 (2007) 3633–3640.R. Dominko, M. Bele, M. Gaberscek, A. Meden, M. Remskar, J. Jamnik, Electrochem. Commun. 8 (2006) 217–222.R. Dominko, M. Bele, A. Kokalj, M. Gaberscek, J. Jamnik, J. Power Sources 174 (2007) 457–461.Y.-X. Li, Z.-L. Gong, Y. Yang, J. Power Sources 174 (2007) 528–532.M. Świętosławski, M. Molenda, M. Grabowska, A.Wach, P. Kuśtrowski, R. Dziembaj, Solid State Ionics 263 (2014) 99–102M. Molenda, M. Świętosławski, A. Rafalska-Łasocha, R. Dziembaj, Funct. Mater. Lett. 4 (2011) 135–138.M. Świętosławski, M.Molenda, K. Furczoń, R. Dziembaj, J. Power Sources 244 (2013) 510–514.

Effect of trivalent rare earth doping on magnetic and magnetocaloric properties of Pr0.5(Ce,Eu,Y)0.1Sr0.4MnO3 manganites

Experimental studies of the structural, magnetic and magnetocaloric properties of the three compounds Pr0.5X0.1Sr0.4MnO3 (X = Ce, Eu and Y) are reported. Our samples were synthesized using the Pechini sol–gel method. X-ray powder diffraction at room temperature indicates that our materials crystallize in the orthorhombic structure with Pbnm space group. The compounds undergo a second-order magnetic transition from paramagnetic to ferromagnetic state around their own Curie temperatures T C ~ 310, 270 and 230 K for X = Ce, Eu and Y, respectively. A considerable magnetocaloric effect (MCE) is observed around room temperature. The maximum values of magnetic entropy change ∆S max are 3.54, 3.81 and 2.99 J/kgK for the samples with X = Ce, Eu and Y, respectively, when a magnetic field of 5 T was applied. The relative cooling power (RCP) values for the corresponding materials are 246.60, 261.66 and 298 J/kg. It is shown that for Pr0.5X0.1Sr0.4MnO3 the exponent n and the magnetic entropy change follow a master curve behavior. With the universal scaling curve, the experimental ∆S at several temperatures and fields can be extrapolated.

Pechini synthesis of Co2SiO4 magnetic nanoparticles and its application in photo-degradation of azo dyes

In this work Co2SiO4 nanoparticles were synthesized via a facile Pechini sol-gel method. The prepared products were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. Alternating gradient force magnetometer (AGFM) illustrates para-magnetic behaviour of Co2SiO4 nanoparticles. The photocatalytic behaviour of Co2SiO4 nanoparticles was evaluated using the degradation of three azo dyes (acid black, acid brown and methyl orange) under ultraviolet light irradiation. The results show that nanocomposites have applicable magnetic and photocatalytic performance. In order to prepare polymeric nanocomposite, Co2SiO4 were added to poly styrene (PS) and polysulfone (PSu) matrices. Outcomes confirm that nanoparticles appropriately enhanced both thermal stability and flame retardant property of the PSu and PS matrices.

Effect of K-doping on the structural, magnetic and magnetocaloric properties of Pr0.8Na0.2–xKxMnO3 (0 ≤ x ≤ 0.15) manganites

In this paper, the effect of potassium “K” substitution on morphological, crystallographic and magnetic properties of the Pr0.8Na0.2MnO3 perovskite was investigated. All samples were synthesized using the Pechini sol–gel method. On the one hand, the morphological study showed that the grains are irregularly spherically-shaped and have a submicronic size. On the other hand, the chemical analysis expectedly unveiled the presence of all the predicted elements in the right composition. Through the X-ray diffraction analysis, we proved that the prepared compounds crystallize in the orthorhombic structure with the Pbnm space group. The temperature dependence of the magnetization M (T) showed a large increase of M when x increases from 0 to 0.05, as does the Curie temperature TC. The transition from ferromagnetic (FM) to charge ordered antiferromagnetic (CO-AFM) phase at high temperature is observed for x = 0, however the doped manganites exhibit only an FM metallic phase. The magnetocaloric effect (MCE) was calculated according to the Maxwell relation based on magnetic measurements. The magnetic entropy change (ΔSM) reaches a maximum value which remains constant when increasing the K content. The highest value of the relative cooling power RCP was found to be 277 J/kg for the Pr0.8Na0.05K0.15MnO3 under an applied magnetic field of 5 T.

Synthesis of a pigment of monodispersive spherical silica particles coated with neodymium disilicate

Spherical silica (SiO2) particles coated with neodymium disilicate (Nd2Si2O7) layer were prepared by a modified Pechini sol-gel method. The phase, structure and morphology of the prepared core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM), respectively. The results reveal that the obtained particles consist of amorphous SiO2 core and crystalline Nd2Si2O7 shell, which have a perfect spherical shape with narrow size distribution, smooth surface and non-agglomeration. The SiO2@Nd2Si2O7 particles possess light-violet and light-blue colors (a*=3.46 and b*=−8.19) due to the characteristic absorption bands of neodymium element. In addition, the formation process of the core-shell SiO2@Nd2Si2O7 particles was also discussed.

Synthesis and characterization of Y2O3 nanoparticles by sol–gel process for transparent ceramics applications

High-purity Y2O3 nanopowder has been prepared by the Pechini sol–gel method using citric acid and ethylene glycol as the chelating agent and complexant of Y3+ cations. The crystal structure of the powder has been studied by means of X-ray diffraction (XRD). In order to evaluate the bonding characteristics of the obtained gel, Fourier transform infrared spectroscopy (FTIR) was carried out. Morphological properties of the nanopowders were examined through field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), respectively. Using spark plasma sintering (SPS) at 1100 °C for 5 min under the uniaxial pressure of 100 MPa, the consolidation of the nanopowder was accomplished. Scanning electron microscopy (SEM) was used to investigate the microstructure of compacted pellets. The compacted specimen was made up of grains in the size range of approximately 40 µm. Furthermore, the optical properties of compacted powder were investigated by means of spectrophotometer. The final obtaining Y2O3 pellet exhibited the in-line transmittance of 60 % at the wavelength of 700 nm.

ChemInform Abstract: Intense Turquoise Colors of Apatite‐Type Compounds with Mn5+ in Tetrahedral Coordination.

AbstractSolid solutions of Ba5Mn3‐xVxO12Cl (x = 0—3.0) (I) and Ba5Mn3‐xPxO12Cl (x = 0—3.0) (II) are prepared by solid state reaction of stoichiometric amounts of BaCO3, MnO2, V2O5, BaCl2, and (NH4)2HPO4 (Al2O3 crucible, 800 °C, 24 h) as well as by Pechini sol gel reaction of Ba(NO3)2, Mn(NO3)2, and NH4Cl in H2O and citric acid at pH 7 followed by calcination of the dried gel in air (700—750 °C, 12 h).

A comparison of the ethanol sensing properties of α-iron oxide nanostructures prepared via the sol–gel and electrospinning techniques

Haematite (α-Fe2O3) nanostructures were synthesized via a Pechini sol–gel method (PSG) and an electrospinning (ES) technique. Their texture and morphology were investigated by scanning and transmission electron microscopy. α-Fe2O3 nanoparticles were obtained by the PSG method, whereas fibrous structures consisting of interconnected particles were synthesized through the ES technique. The crystallinity of the α-Fe2O3 nanostructures was also studied by means of x-ray diffraction and Raman spectroscopy. Gas-sensing devices were fabricated by printing the synthesized samples on ceramic substrates provided with interdigitated Pt electrodes. The sensors were tested towards low concentrations of ethanol in air in the temperature range (200−400°C). The results show that the α-Fe2O3 nanostructures exhibit somewhat different gas-sensing properties and, interestingly, their sensing behaviour is strongly temperature-dependent. The availability of active sites for oxygen chemisorption and the diffusion of the analyte gas within the sensing layer structure are hypothesized to be the key factors responsible for the different sensing behaviour observed.

Highly stable and selective ethanol sensor based on α-Fe2O3 nanoparticles prepared by Pechini sol–gel method

In the present work, α-Fe2O3 nanoparticles were successfully synthesized by Pechini sol–gel (PSG) method following annealing at 550°C. The morphology and microstructure of the prepared α-Fe2O3 nanoparticles were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman analysis. The electrical and sensing properties were also investigated. The α-Fe2O3 based sensor showed good sensitivity and selectivity towards ethanol at the optimal temperature of 225°C. Moreover, the sensor displayed good electrical and sensing stability. These results suggest the potential applications of α-Fe2O3 synthesized by Pechini sol–gel method as a sensor material for ethanol detection.

Preparation and Characterization of Titania-silica Composite Particles by Pechini Sol-gel Method

Two Pechini sol-gel processes were used to prepare titania-silica composite particles. The dynamic oxidation behavior of the TiO 2 -SiO 2 powders has been characterized by thermogravimetry-differential scanning calorimetry (TG-DTG-DSC). The crystal phase and microstructure of the composite particles were investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The effects of Si:Ti molar ratio and sol-gel process on the TiO 2 -SiO 2 powders were studied. The preparation of the polymeric precursors can influence the morphology of obtained TiO 2 -SiO 2 composite particles. The spherical TiO 2 -SiO 2 composite particles which are 20 nm~400 nm in diameter appear in gel-1 system. However, the TiO 2 -SiO 2 powders obtained by gel-2 system are irregular in shape and 2~15 μm in diameter which show a loose porous structure consisted of very fine granules.

Preparation of chromatic composite hollow nanoparticles containing mixed metal oxides for full-color electrophoretic displays

The green and blue hollow nanospheres were prepared via emulsifier-free emulsion polymerization and the Pechini sol–gel process. They exhibit bright color and hollow structures with uniform size and shape, which also present excellent performance and quick response of electrophoretic display.

Synthesis, structure and upconversion luminescence of Yb3+, Ho3+co-doped Gd3Al5O12garnet phosphor prepared by the Pechini sol–gel method

A pure-phase phosphor of Gd3Al5O12garnet (GAG) co-doped with Yb3+and Ho3+ions has been synthesized by the Pechini sol–gel method.

Enhanced visible light absorption and photocatalytic activity of [KNbO3]1−x[BaNi0.5Nb0.5O3−δ]x synthesized by sol–gel based Pechini method

[KNbO3]1−x[BaNi0.5Nb0.5O3−δ]x were synthesized by Pechini sol–gel method at low temperature. Visible light photocatalytic performance of this material was evaluated.

Optimization of Dye-sensitized Solar Cells Prepared by Pechini Sol-Gel Method

Functional TiO2 films were prepared by using a facile one-step Pechini Sol-Gel method. The intrinsical contribution mechanism of film thickness to the photo-to-electric performance of DSSC was explored with analysis of interfacial charge recombination effects, on which, the characteristics of DSSC were optimized via film thickness controlling. The influence of TiO2 film thickness on dye absorption, charge recombination process and photovoltaic performance of DSSC were by UV-Vis, electrochemical impedance spectroscopy and I-V test under dark condition, respectively. The results show that as TiO2 film thickness increases, the light harvesting efficiency and photocurrent of DSSC increase, which were induced by the enhancement of dye absorption. However, the photovoltage decreases gradually with the increaese of electron recombination probability. As an increase, combination of the positive and negative effects above enables the Pechini-type DSSC efficiency first increase and then decline, with an optimum efficiency of 7.75% at the film thickness of 10.7 μm, in contrast to 6.5% of the routine method.

Effect of Li+ and Zn2+ co-doping on PL properties of Y2O3:Eu3+ phosphor

In this paper we have reported the effect of co-doped on the luminescence properties of Y2O3:Eu3+ phosphors. The Y2O3:Eu3+ phosphors prepared by different methods such as combustion synthesis, precipitation methods, Pechini sol–gel method. XRD, SEM and FTIR analysis were carried out for the confirmation of phase purity, surface morphology and MO vibration in host lattice. Here we focused on the more desired route of synthesis of Y2O3:Eu3+ phosphor for high lumen output with low cost synthesis route. Detailed study has been presented on the emission properties of Y2O3:Eu3+ (Eu=1m%) due to various concentration of Li+ and Zn2+ by urea combustion method, precipitation method and Pechini sol–gel method. In this investigation, we found that PL intensity strictly depends on the method of preparation and concentration of co-dopant Li/Zn, in sample Y2O3:Eu3+ (Eu=1m%), and intensity of red emission peak enhances by, accountable factor by adding Li+ and Zn2+ in Y2O3:Eu3+. Thus the prepared phosphor is a promising red phosphor used in lamp industries.

Synthesis and characterization of ZnO–TiO2 nanopowders doped with fe via sol–gel method and their application in photocatalytic degradation of anionic surfactant

ZnO and 0, 5, and 10 mol % Fe-doped ZnO–TiO2 nanopowders were synthesized by the sol–gel Pechini method. The successful synthesis of coupled ZnO–TiO2 nanopowders was evident by XRD. Scanning electron microscopy (SEM) revealed that the Fe ions were well incorporated into the ZnO–TiO2 crystal lattice. The photocatalytic degradation of anionic surfactant (linear alkylbenzene sulfonate (LABS), was investigated in aqueous solution using ZnO and Fe-doped ZnO–TiO2 nanoparticles. The degradation was studied under different conditions such as the Fe3+ concentration, amount of photocatalyst, irradiation time, pH, initial concentration and presence of electron acceptor. The results showed that photocatalytic degradation of LABS was strongly influenced by these parameters. The best conditions for the photocatalytic degradation of LABS were obtained. It is found that under UV light irradiation, Fe-doping of ZnO–TiO2 increases the efficiency of its photocatalytic activity in degradation of LABS than pure ZnO and ZnO–TiO2.

Substitution-driven enhanced magnetic and ferroelectric properties of BiFeO3 nanoparticles

Multiferroic BiFeO3 (BFO) nanoparticles along with co-substitution of Gd, a rare-earth element, and Co, a transition metal, were synthesized through modified Pechini sol–gel process. A compositional-driven structural change in the rhombohedral phase (R3c) due to the inclusion of Gd and Co was identified with the help of X-ray diffraction analysis. Dense oblate nanospheres with average grain sizes less than the spin periodicity of BFO were observed through field emission scanning electron microscopy studies, where the grain sizes were found to decrease with increasing concentration of substituent ions. The co-substitution modified the BFO's original magnetic structure, which eventually led to the enhancement of spontaneous magnetization as evident from their M−H hysteresis loops. Large difference between ZFC and FC curves indicates some glassiness in the co-substituted samples. In addition to the observed distortion in crystal structure, a considerable reduction of Fe2+ ions confirmed by XPS has favored enhancement of polarization.

Compositional dependence of the crystal symmetry of Eu3+-doped (SrxBa1−x)2CaWyMo1−yO6 phosphors

Two series of A-site and B-site Eu3+ doped (SrxBa1−x)2CaWyMo1−yO6 double perovskite phosphor materials were prepared via a modified Pechini sol–gel route; (SrxBa1−x)1.96Eu0.02K0.02CaWyMo1−yO6 and (SrxBa1−x)2Ca0.96Eu0.02Li0.02WyMo1−yO6 (x and y=0, 0.25, 0.50, 0.75, 1). The Sr/Ba ratio was the main determinant for the crystal symmetry of the series, while variation in the W/Mo ratio did influence the crystal symmetry significantly. The crystal structure evolved with Sr/Ba ratio from cubic Fm3¯m for x=0, via tetragonal I4/m for x=0.25, to monoclinic P21/n for x≥0.5, as verified by Rietveld refinement of X-ray diffractograms as well as by Raman spectroscopy. The reported boundaries for the compositionally induced phase transitions are in very good agreement with reported optical properties.