Pechini Method Research Articles

Synthesis, crystal structure and spectroscopic characterization of a new cadmium phosphate, Na2Cd5(PO4)4

A novel cadmium phosphate compound Na2Cd5(PO4)4 was synthesized in single crystal and in powder forms using flux and Pechini methods, respectively. It was then characterized by single crystal X-ray diffraction, vibrational spectroscopy and photoluminescence measurements. This compound crystallizes in the monoclinic system with space group P21/a, lattice parameters a = 8.276(1) Å, b = 9.301(3) Å, c = 9.455(2) Å, β = 111.82 (1)° and Z = 2. The structure consists of (Na3/4,Cd1/4)O7, (Cd3/4,Na1/4)O6 and CdOx (x = 6, 7), polyhedra and PO4 tetrahedra linked through common corners or edges giving rise to a novel type of complex three-dimensional framework. This structure could be described in terms of [(Na3/4,Cd1/4)2(Cd3/4,Na1/4)2Cd3O16]∞ layers stacked parallel to the (2 0–3) plane and interconnected both directly and via PO4 tetrahedra by sharing common corners and edges. Vibrational spectroscopy and cadmium photoluminescence were analyzed according to the structural results.

The synthesis of SmCo/Co nanoplates: reductant effect in the synthesis process

In search for improvement in synthesizing the nanoparticles, specifically for rare earth-transition metals (Re-Tm), Pechini method was employed followed by thermal oxidation process. The SmCo nanoplates were formed due to a reduction–diffusion phenomenon. A range of characterization techniques including XRD, FE-SEM, and VSM were used for further investigations. Hard phases of SmCo5 and Sm2Co17 were obtained by adjusting the ratios of the solutes. The presence of cobalt, as the soft phase along with SmCo, as well as the single-phase behavior of magnetic hysteresis loop together with the high remanence ratio of the synthesized nanoplates, confirmed the hard–soft exchange coupling interaction. The data also indicated that hydrogen was not sufficient to act as a reducing agent; significant amount of CaH2 was added to the mixture. The quantity of CaH2 and consequently its weight ratio to the oxide powder had an effect on the synthesis process and final products in different aspects, including the evolution, microstructure, morphology, and magnetic properties. Eventually, when the weight ratio CaH2/oxide powder was kept at 2:1 the SmCo5 was the dominant phase of the nanoplates; whereas, for the 3:1 mixture, Sm2Co17 was the prominent, containing distinguishable nanoplates of Sm2Co17/Co with the average thickness of 32 nm.

Nickel Exsolution‐Driven Phase Transformation from an n=2 to an n=1 Ruddlesden‐Popper Manganite for Methane Steam Reforming Reaction in SOFC Conditions

AbstractAn original way to perform the exsolution of Ni nanoparticles on a ceramic support was explored for the development of methane steam reforming catalyst in SOFC anode conditions. The n=2 Ruddlesden‐Popper (RP) phase La1.5Sr1.5Mn1.5Ni0.5O7±δ has been synthesized by the Pechini method and subsequently reduced with an H2‐N2 mixture at different temperatures and reducing times to induce the formation of two phases: LaSrMnO4 (n=1 RP) decorated with metallic Ni nanoparticles. Preliminary measurements of catalytic behavior for the steam reforming have been carried out in a reduction‐reaction process with a mixture of 82 mol %CH4, 18 mol %N2 and low steam to carbon ratio (S/C=0.15). The catalyst exhibits a selectivity for CO production (0.97), 14.60 mol % CH4 conversion and around 24.19 mol % H2 production. Such catalytic behavior was maintained for more than 4 h, with a constant rate of hydrogen production and CH4 conversion rate.

Multicomponent Co-based sol–gel catalysts for dry/steam reforming of methane

The multicomponent Со–Pt–Zr/Al2O3 and Со–Pt–Zr–La/Al2O3 catalysts were prepared by the sol–gel method. The modified Pechini method was used as a sol–gel approach to synthesize a system containing Co, Pt, Zr, and La. The sol–gel materials prepared by such a manner were incorporated into alumina in order to form the catalyst granules. The physicochemical properties of the catalysts were studied by a number of methods (TEM, SEM, BET, XRD, H2-TPR). It was found that the synthesized multicomponent catalysts are highly dispersed systems composed of metal oxides and various microalloys such as the bimetallic Co–Pt and perovskite type structures—LaCoO3 and LaAlO3 having mainly the particle size 200 h.

Investigation on Hydration Process and Biocompatibility of Calcium Silicate-Based Experimental Portland Cements

In this work, the hydration process and cytotoxicity of lab-synthesized experimental Portland cements (EPCs) were investigated for dental applications. For this purpose, EPCs were prepared using laboratory-synthesized clinker constituents, tricalcium silicate (C3S), dicalcium silicate (C2S), and tricalcium aluminate (C3A). C-A was prepared by the Pechini method, whereas C3S and C2S were synthesized by solid-state reactions. The phase compositions were characterized by X-ray diffraction (XRD) analysis, and the hydration process of the individual constituents and their combinations, with and without the addition of gypsum, was investigated by electrochemical impedance spectroscopy (EIS). Furthermore, four EPC compositions were prepared using the lab-synthesized C-A, C3S, and C2S, and their hydration processes were examined by EIS, and their cytotoxicity to HPC and HIPC cells were tested by performing an XTT assay. None of the EPCs exhibited any significant cytotoxicity for 7 days, and no significant difference was observed in the cell viabilities of ProRoot MTA and EPCs. The results indicated that all the EPCs are sufficiently biocompatible with human dental pulp cells and can be potential substitutes for commercial dental cements. Key words: Experimental Portland cement, Hydration process, Electrochemical impedance spectroscopy, Cytotoxicity, Dental cement

Enhanced electrochemical performance of nanopyramid-like LiMnPO4/C cathode for lithium–ion batteries

In this study, Nano-pyramid like LiMnPO4/C material is synthesized by using the modified Pechini method and it's structural, morphological and the electrochemical properties are studied. The result obtained through the X-ray diffraction analysis confirms an orthorhombic structure of LiMnPO4/C. The Fourier infrared spectroscopy and X-ray photoelectron spectroscopy reveals the presence of PO4 group. On the other hand, Electron microscopy images reveal the existence of a pyramid shaped particle. The observation of the Galvanostatic charge-discharge indicates that the synthesized LiMnPO4/C nanopyramid delivers the first discharge capacity of 164.2 mAh g−1 at C/10 rate. It also maintained the discharge capacity of 130.8 mAh g−1 at the 500th cycle. Conductive carbon coating and nanopyramid like morphology increases the Lithium diffusion kinetics and conductivity. Thereby there is an improvement in the electrochemical performance of LiMnPO4/C cathode material.

Effect of annealing temperature and chelating agent concentration on the phase evolution, morphology and heavy metal removal efficiency of nanosized spinel

In this research, using the precursors of Al(NO3)3.9H2O and Mg(NO3)2.6H2O as the source of Al3+ and Mg2+ and different molar ratios of diethylene glycol (DEG) and succinic acid (C4H6O4) as a gel and chelating agent, magnesium aluminate (spinel) nanoparticles were prepared by modified sol-gel (Pechini) method. The x-ray diffraction results confirmed the formation of single-phase magnesium aluminium spinel nanoparticles with a cubic crystal structure at 800 °C. Scanning electron microscopy (SEM) was also shown that the prepared nanoparticles with succinic acid to ethylene glycol mole ratio ¾ of having a quasi-spherical morphology with an average size between 40–50 nm. In addition, the prepared nanoparticles were used as adsorbents to remove lead and cadmium contaminants from heavy ion-containing water. To investigate the adsorption process, adsorption kinetics and equilibrium isotherms for lead and cadmium ions were investigated, and it was found that the adsorption process for two ions follows the second-order kinetic.

High CO2-tolerance oxygen permeation dual-phase membranes Ce0.9Pr0.1O2-δ-Pr0.6Sr0.4Fe0.8Al0.2O3-δ

High stability and oxygen permeability are two prominent requirements for the oxygen transport membrane candidates used as industrialization. Herein, we report several composite membranes based on xwt.%Ce0.9Pr0.1O2-δ (CPO)-(100-x)wt.%Pr0.6Sr0.4Fe0.8Al0.2O3-δ (PSFAO) (x = 50, 60 and 75) prepared via a modified Pechini method. Oxygen permeability test reveals that the 60CPO-40PSFAO composition exhibits the highest oxygen permeability. The oxygen permeation flux through the optimal uncoated 0.33 mm-thickness 60CPO-40PSFAO composite can reach 1.03 mL cm-2 min-1 (over the general requirement value of 1 mL cm-2 min-1) in air/He atmosphere at 1000 °C. In situ XRD performance confirms the optimal 60CPO-40PSFAO sample shows excellent stability in CO2-containing atmospheres. The 60CPO-40PSFAO membrane still exhibits simultaneously excellent oxygen permeability and phase stability after operating for over 100 h at air/CO2 condition at 1000 °C, which further indicates that the 60CPO-40PSFAO composite is likely to be used for oxygen supply in CO2 capture.

Optical nanothermometry under multiphonon assisted anti-Stokes excitation operating in the biological windows

In this work, we report a potential nanothermometer with high thermal sensitivity based on sodium niobate (NaNbO3) nanocrystals doped and co-doped with Tm3+ and Tm3+/Yb3+, respectively, synthesized by the Pechini (sol–gel) method. Under anti-Stokes excitation (1064 nm) it was investigated the fluorescence intensity ratio (FIR=I700nm/I660nm) of the 700 nm (3F2,3 → 3H6) and 660 nm (1G4 → 3F4) emissions, which are within the first biological window, as a function of temperature in the 300–493 K range. Relative thermal sensitivities constant with the temperature were obtained, with values of 1.60% K−1 and 1.86% K−1 for NaNbO3:1%Tm3+ and NaNbO3:1%Tm3+/1%Yb3+ samples, respectively, which is the highest value in the literature for Tm3+/Yb3+ co-doped system under 1064 nm excitation. The importance of the anti-Stokes excitation relies on the fact that emissions (up and downconversion) in general increase with the temperature, making possible obtaining fluorescence and thermal images with better resolutions. Additionally, as both excitation and emission are within the biological windows, these nanoparticles might be useful for biological applications.

Alkaline-earth-free quasi-ternary La(Co, Ni, Fe)O3−δ perovskite as potential cathode for solid oxide fuel cells

The purpose is to develop alternative alkaline-earth-free quasi-ternary LaCoO3−LaNiO3−LaFeO3 cathode materials for solid oxide fuel cells (SOFCs), which demonstrate high electrical conductivity, good electrochemical performance and excellent chemical stability against CrO2(OH)2 released from the metallic interconnects at operation temperatures. Three different perovskites of lanthanum in combination with iron, cobalt and nickel oxides, i.e. LaFe0.8Co0.1Ni0.1O3−δ (LFCN), LaNi0.8Co0.1Fe0.1O3−δ (LNCF) and LaCo0.8Fe0.1Ni0.1O3−δ (LCFN), were synthesized by the modified Pechini method, and then systematically investigated in the phase structure, thermal expansion, electrical conductivity and catalytic activity. LFCN have the best combination to the requirements of high-performance cathodes for SOFCs. Button cells with LFCN cathode were prepared on anode-supported YSZ electrolyte with gadolinium-doped cerium (GDC) buffer layer by screen printing. Excellent electrochemical performance with high maximum power density of 643 mW.cm−2 at 750 °C and corresponding low polarization resistance of 0.62 Ω cm2 further demonstrate that LFCN is a very competitive candidate as SOFC cathode.

“Frozen” pressure effect in GGAG:Ce3+ white light emitting nanoceramics

Nanocrystalline powders of Ce3+ doped Gd3Ga3Al2O12 (GGAG) with the size of tens nanometers were prepared using modified Pechini method. Low Temperature High Pressure sintering method was used for the fabrication of the translucent nanoceramics using as starting materials nanocrystalline GGAG:Ce3+ powders. For growth of GGAG:Ce single crystal the Czochralski method was utilized. XRD measurement was used in order to characterize the grain size of the GGAG:Ce3+ nanostructures. Excitation and emission and luminescence decays measurements were done to observe impact of the grain size and applied pressure on the spectroscopic properties of crystallites and ceramics. It was observed that for the smallest grains both spectra are significantly changed. The spectroscopic properties of the nanopowders were compared to the GGAG:Ce3+ ceramics made from them as well as to the single crystal. It was found that is possible to modify permanently the crystal field in the nanocrystals by applying the pressure during sintering.

ZnO nanoparticles with tunable bandgap obtained by modified Pechini method

Zinc oxide nanoparticles (N–ZnO) obtained by the Pechini method and calcined using a closed clay container are the focus of the present work. The synthetic route includes a modification in the calcination process (modified Pechini method), that is, without the change in the calcination process. The modified calcination process carried out in a clay container allows for the tunability of the ZnO bandgap. To characterize the materials, X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible (UV–Vis) spectroscopy have been performed. The analysis of UV–Vis absorption measurements allows us to conclude that the bandgap of N–ZnO can be tuned from 2.8 to 3.04 eV for ZnO–CC:400 and ZnO–CC:600 (samples of carbon-doped N–ZnO or C–N–ZnO), respectively, which are smaller than the ZnO bulk value of 3.37 eV. This gives rise to new possibilities of adaptation for the N–ZnO to new applications by shifting the bandgap from the UV to the visible region. The XRD and TEM measurements show that all samples are highly crystalline and have small grain sizes, confirming that the ethylene glycol seems to be a useful polymerizing agent for the preparation of C–N–ZnO.

Fabrication and Performance of La, Co-Substituted SrTiO3 as Cathode Materials of Solid Oxide Fuel Cell

SrTiO3-based materials have been investigated to be a candidate for anode of solid oxide fuel cell (SOFC) due to good chemical stability and high ionic conductivity in reducing atmosphere. However, the electronic conductivity is relatively low, which might be increased by doping. In this work, La, Co-substituted SrTiO3 (LSTC) was fabricated and evaluated as cathode of SOFC. Pechini method was successfully used for material synthesis. By doping of La and Co, the conductivity of materials can be increased to more than 1 S/cm at 800 °C. LSTC|Gadolinium-doped ceria|LSTC symmetric cells were also fabricated for electrode performance testing. The results showed that the interface resistance of LSTC cathode can be optimized to be 0.02 Ω·cm2 at 800 °C and 0.3 Ω·cm2 at 600 °C, which indicates possible application of LSTC cathode materials for SOFC. Maximum power density of LSTC cathode on button-sized anode-supported SOFC reached 0.360 W/cm2 at 800 °C.

Synthesis and Characterization of a New Electrolyte Composition for Protonic SOFC

This work focuses on the research of high efficiency and durability materials for use in protonic solid oxide fuel cells. The focused material on this stage of research is BaZr0.4Ce0.4Y0.1Gd0.1O3-δ (BZCYG); it attempts to join the good proton conductivity of barium cerate with the chemical stability of barium zirconate. Its synthesis is done via the modified Pechini method (1) using nitrates of the desired ions. The property characterization methods used were TGA/DSC, to determine the calcination temperature; dilatometry to assess the sintering behavior with and without sintering aid (NiO, as found in the literature (2)); X-ray diffraction (XRD) to make sure the desired phase was obtained; and Electrochemical Impedance Spectroscopy (EIS) to assess the protonic conductivity. The main problem faced while dealing with materials of this kind is their poor sinterability (3). The ideal composition was obtained, with single phase formation being identified through XRD.

Enhancement in the photocatalytic activity of Bi2Ti2O7 nanopowders synthesised via Pechini vs Co-Precipitation method

Abstract Bi2Ti2O7 nanopowders were synthesised via two different methods i.e. Pechini (P) and Co-Precipitation (C) method by annealing at 550 °C for 16 h. The effect of synthesis technique on photocatalytic activity of Bi2Ti2O7 nanopowders was extensively studied. Formation of pure Bi2Ti2O7 pyrochlore phase was observed in both samples. Various crystallographic parameters obtained by reitveld analysis of X-Ray Diffraction (XRD) spectra of both samples infer the formation of a highly loose crystallographic structure in P sample. The smaller crystallite size of P sample correlates with the observed blue shift in the Raman spectra, furthermore decreasing the particle size in P sample. P sample exhibits higher specific surface area, mean pore diameter and total pore volume which is inferred by Brunauer-Emmett-Teller (BET) analysis. Higher photocatalytic activity of P sample can be attributed to the formation of distorted crystallographic structure and higher specific surface area.

GO/C2S Gate Dielectric Material for Nanoscale Devices Obtained via Pechini Method

Some issues, such as leakage and tunneling currents, and light atom penetration through a thin gate dielectric, are threatening for silicon dioxide to be used as a suitable gate dielectric material for the next-generation metal-insulator-semiconductor-field-effect-transistor (MISFET) devices. A novel gate dielectric material for MISFET has been synthesized via the Pechini method by combining graphene oxide (GO)/dicalcium silicate (C2S) components. First, GO nanoparticles were synthesized via the Hummer method and C2S—via the Pechini method and then 0.1, 0.2, 0.4 and 0.8 the weight percentages (wt %) of GO were added into the C2S matrix. Their nanostructural properties were studied by the field emission scanning electron microscopy X-ray diffraction, Fourier transform infrared, thermo-gravimetry and differential scanning calorimetry. The electrical properties of GO/C2S nanocomposites, metal (Al)-GO/C2S insulator-Si (semiconductor) were fabricated by the physical vapor deposition technique at 10–7 Torr. The capacity, current-voltage relationship, quality factor, dissipation factor were measured with an LCR meter GPS-132A and 4-probe techniques. The frequency response of dielectric properties, dielectric constant, dielectric loss, and AC electrical conductivity, of the examined samples were studied. The electrical measurements showed that a sample with 0.4 wt % of GO nanoparticles has a higher dielectric constant at a frequency of 120 kHz (K = 62) and 1 kHz (K = 30), a lower leakage current (20 × 10–6 A/cm2), a good carrier mobility (7.62 cm2/V s), a low threshold voltage (2.9 V), a large current ION/IOFF ratio (1.25 × 103), and a higher quality factor (32.4). Therefore, C2S/GO nanocomposite with 0.4 wt % Go nanoparticles can be introduced as an alternative gate dielectric material for the next generation of MISFET devices.

Effects of Al content on the oxygen permeability through dual-phase membrane 60Ce0.9Pr0.1O2--40Pr0.6Sr0.4Fe1-Al O3-

Ceramic dual-phase oxygen transport membranes with the composition of 60wt.% Ce0.9Pr0.1O2-{\delta}-40wt.%Pr0.6Sr0.4Fe1-xAlxO3-{\delta} (x = 0.05, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0) (60CPO-40PSF1-xAxO) based on 60Ce0.9Pr0.1O2-{\delta}-40Pr0.6Sr0.4FeO3-{\delta} doped Al was successfully synthesized through a modified Pechini method. Crystal structure, surface microtopography and oxygen permeability are investigated systematically. The cell parameters of perovskite phase first increased and then decreased with the increase of Al content, which is related to the radius of the Al3+ and the formation of impurity phase. As x ranges from 0.1 to 0.8, the oxygen permeability of the materials first increases and then decreases, and the maximum value of oxygen permeation rate for 60CPO-40PSF1-xAxO membranes with 0.4mm thickness at 1000 {\deg}C is 1.12 mL min-1 cm-2 when x = 0.4. XRD measurements revealed high temperature stability and CO2-tolerant property of the dual-phase composites. The partial replacement of Fe$^{3+}$/Fe$^{4+}$ by Al$^{3+}$ causes the material not only to exhibit good stability, but also to increase the oxygen permeability of the membranes.

Vanadium-substituted Sm2Ti2O7 pyrochlore. Insight into the structure and electrical conductivity under oxidizing and highly reducing atmosphere

With the aim to increase the conductivity of Sm2Ti2O7 in reducing atmosphere characteristic to the anodic side of the SOFC by partial substitution of titanium site with vanadium, crystalline phases, reduction behavior and transport properties of vanadium-doped Sm2Ti2O7 were investigated in this study. Sm2Ti2-xVxO7±δ (x = 0; 0.1; 0.2) powders have been synthesized using a modified Pechini method. After thermal treatment in air, the presence of monoclinic secondary phase was evidenced by X-ray diffraction analysis and Raman spectroscopy, while thermal treatment in 2% H2/Ar mixture led to single-phase pyrochlore structures. H2-TPR analysis revealed the high reducibility of vanadium-substituted sample. The electrical conductivities of the investigated sample in air are quite small, mainly due to the presence of secondary phase. The decrease in oxygen partial pressure led to a high increase in overall conductivity due to the n-type electronic component. Sample with 5% V on Ti exhibited the highest increase in conductivity when switching from air to hydrogen-containing atmosphere.

On the stable coexistence of the orthorhombic and rhombohedral symmetries in BiFeO3 compound

BiFeO3 nanoparticles (<200 nm) were synthesized using the Pechini method and submitted to structural, microstructural, magnetic and electrical investigations. Two different structural symmetries were proposed to describe the BiFeO3 structure and the observed electrical properties, rhombohedral (R3c space group) and orthorhombic (Pbmn). Electric conductivity results obtained as a function of temperature, show two completely reversible changes in the baseline (310 °C and 385 °C), indicating two magnetic corresponding transitions associated with the orthorhombic and rhombohedral symmetries. These transitions were linked to predicted insulating-metal transition when magnetic arrangement changes from antiferromagnetic to a nonmagnetic ordering.

Vibrational and magnetic properties of YIG ferrite powders obtained by the Pechini method

Yttrium iron garnet (YIG: Y3Fe5O12) ferrite powders were obtained by the Pechini method from metal nitrates, citric acid and ethylene glycol followed by thermal annealing at Tan = 900°C, 1000°C, 1100°C and 1200°C. X-ray diffraction (XRD) and Raman spectroscopy were used to study the structural and vibrational properties of YIG powders. Raman spectra of powders showed the same set of bands as the bulk YIG, but they are broadened due to spatial confinement of phonons. Magnetic properties were measured by vibrant sample magnetometer (VSM), founding that magnetic properties are strongly dependent on Tann; in particular the magnetization increases and reaches the bulk value of 27.7 emu/g at T = 1000°C.