Polymeric Citrate Precursor Research Articles

Short review on fabrication, structural and dielectric characterization of zirconium based oxide nanoparticles

Zirconum based oxide nanoparticles of general formula Ba1-xPbxZrO3 and Ba1-xSrxZrO3with dopant concentrations ranging from 0 to 1 using reverse micellar and polymeric citrate precursor methods are discussed. Presently, hundreds of dielectric materials have currently been synthesized. Zirconium-based oxides are the significant class of dielectric materials among them because of their structural flexibility and simplicity. This review summarizes recent advances in zirconium-based oxide synthetic strategies, their significant use as dielectric materials for wireless communication devices such as electroceramics and piezoelectric devices, and efforts being made to alter their physicochemical properties and increase their efficiencies by adjusting reaction conditions. The article's goal is to describe approaches controlling these materials' efficacy and upcoming difficulties for practical applications.1–3

Exploiting multiferroicity of TbFeO3 nanoparticles for hydrogen generation through photo/electro/photoelectro-catalytic water splitting

Hydrogen is a potential future energy source that could replace conventional fuel and provide the necessary energy. Multiferroic materials are the most likely choices for water splitting due to their ferroelectric characteristics and ability to function as magnetically recoverable catalysts. Multiferroic terbium orthoferrite nanoparticles were synthesized at low temperature by the polymeric citrate precursor route to study the photocatalytic, electrocatalytic and photoelectrochemical activity towards hydrogen production. Powder X-ray diffraction revealed successful formation of orthorhombic TbFeO3 nanoparticles. A larger aspect ratio of 3.9 and a bandgap of 2.13 eV were seen in the elongated TbFeO3 nanoparticles, which contributes to the photo/electro-catalytic activity. Magnetic and ferroelectric studies revealed weak ferromagnetism and ferroelectric polarization of 0.037 μC cm−2 in TbFeO3 nanoparticles, confirming multiferroicity. Visibly active and multiferroic TbFeO3 nanoparticles showed notable hydrogen evolution of 1.44 mmol h−1 g−1. In electrocatalytic and photoelectrochemical water splitting investigations, TbFeO3 nanoparticles demonstrated current densities of 30 and 60 mA cm−2, respectively. EIS, TRPL, transient photocurrent and Mott-schottky measurements were used to examine charge transfer kinetics. The high H2 evolution and good OER/HER tests were attributed to increased charger separation efficiency due to ferroelectricity induced band bending.

Review on Polymeric Citrate Precursor and Sono-chemical Methods for the Synthesis of Nanomaterials

Background: he properties of materials depend on the way of construction and the arrangement of atoms and molecules. Therefore, it is very important to know synthesis methods for the preparation of novel materials as per their desired structure. The low-temperature synthesis methods, such as polymeric citrate precursor and sonochemical methods are efficient enough to control the preparation of novel nanoparticles with morphological differences that leads to the novel devices with desired technological performances. These methods are simple, very less expensive and are easy to handle to operate for the synthesis of nanoparticles as per the expected morphology and dimensions. Methods: Polymeric citrate precursor method, a chelate-based method involves the reaction between mixed cations with citric acid, and then these cations are cross-linked with the help of ethylene glycol for the esterification process. Gel composites were heated which burns the organic moieties leaving behind the nanoparticles, and burning gels becomes essential for the reduction of nanoparticles. The sonochemical method, on the other hand, uses ultrasonic the irradiation results. The acoustic cavitation and high intensity ultrasound has been exploited for the preparation of different series of nanoparticles. Results: Commonly known for polymeric citrate method as Pechini gel pyrolysis method gives the evidence of versatile and elegant method for the synthesis of nanoparticles. The sonochemical method provides an unusual route of nanoparticle fabrication without bulk and that too with low temperature and pressure or less reaction time. These two methods have better control for the desired shape morphology and size and provide many opportunities for the use of these prepared nanoparticles in various aspects of science and technology. Conclusion: Polymeric citrate precursor and sonochemical methods are efficient to reduce to promote desirable reaction conditions and reduce the metal ions for the fabrication of nanoparticles. The prepared nanoparticles by using such low-cost elegant methods are uniform with a small size distribution, reproducible with good yield as per the demanded applications.

High-Surface-Area Sodium Tantalate Nanoparticles with Enhanced Photocatalytic and Electrical Properties Prepared through Polymeric Citrate Precursor Route.

NaTaO3 nanoparticles with a high surface area of 46.2 m2/g have been successfully synthesized using a polymeric citrate precursor route. As-prepared nanoparticles were extensively characterized by X-ray diffraction, Fourier transform infrared, transmission emission microscopy, and scanning electron microscopy studies for the analysis of phase purity, crystallinity, and morphology. NaTaO3 nanoparticles show efficient photo-induced removal of the methylene blue dye under sunlight, which were confirmed by using liquid chromatography–mass spectroscopy. 86% dye has been degraded in 200 min at neutral pH, whereas the same amount of dye was decolorized in only 80 min at alkaline pH. Also, the dielectric behavior of the as-prepared nanoparticles at different annealing temperatures was explained by the Maxwell–Wagner polarization mechanism. At 500, 600, and 700 °C annealing temperatures, the dielectric constant and dielectric loss at 500 kHz for the samples were found to be 21.5, 18, and 16 and 0.012, 0.022, and 0.029, respectively. The unsaturated hysteresis loop shows weak ferroelectric behavior of NaTaO3 nanoparticles with remanent and saturation polarizations of 0.0013 and 0.21 μC/cm2, respectively, and S-E hysteresis shows a bipolar strain of 0.10%.

Synthesis, characterization and dielectric properties of $$\hbox {TiO}_{2}$$ TiO 2 – $$\hbox {CeO}_{2}$$ CeO 2 ceramic nanocomposites at low titania concentration

\(\hbox {TiO}_{2(x)}\)–\(\hbox {CeO}_{2(1-x)}\) nanocomposites were prepared at low \(\hbox {TiO}_{2}\) composition of 5, 10, 15 and 20%, by using \(\hbox {TiO}_{2}\) and \(\hbox {CeO}_{2}\) nanoparticles obtained by polymeric citrate precursor method. These nanocomposites were characterized by using powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive analysis of X-rays and BET surface area studies. BET studies showed the specific surface area of as-prepared nanocomposites in the range of 239–288 \(\hbox {m}^{2}~\hbox {g}^{-1}\). Twenty percent of \(\hbox {TiO}_{2}\)-based titania–ceria nanocomposites have smallest average particle size of 30 nm and highest surface area of 288 \(\hbox {m}^{2}~\hbox {g}^{-1}\) among all the as-prepared nanocomposites. The dielectric characteristics were measured as a function of frequency and temperature. The dielectric constant of \(\hbox {TiO}_{2(x)}\)–\(\hbox {CeO}_{2(1-x)}\) at room temperature was 35.6 (maximum) at 500 kHz for \(x = 0.20\).

Structural characterization and dielectric properties of ceria–titania nanocomposites in low ceria region

(x)CeO2-(1−x)TiO2 nanocomposites have been prepared by means of CeO2 and TiO2 nanoparticles synthesized by polymeric citrate precursor route at low CeO2 compositional concentration of 5%, 10%, 15% and 20%. As-prepared nanocomposites were investigated by using powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy and BET surface area studies. The specific surface area of as-prepared CeO2–TiO2 ceramic nanocomposites was found to be in the range of 181–210 m2 g−1. 5% CeO2 based ceria–titania nanocomposite was found to have smallest average particle size of 40 nm and highest surface area of 210 m2 g−1. Dielectric properties were measured with variation of frequency and temperature. The room temperature dielectric constant of (x)CeO2-(1−x)TiO2 was found to be maximum (61.8) at 500 KHz frequency for x = 0.05.

Processing of 0.7BaTiO3-0.3BiScO3Solid-Solution Coatings

Coatings with the 0.7BaTiO3–0.3BiScO3 solid-solution composition were formed on palladium and single-crystal (001) SrTiO3 substrates using a polymeric metal citrate precursor. Solutions of TiOCl2, Ba(NO3)2, Sc(NO3)3, and Bi(NO3)3 were mixed with citric acid and polymerized with ethylene glycol. Stable mixed-metal citrate solutions were formed at pH > 9 and used for coatings. The phase and composition of powders and coatings were characterized using DTA, TGA, SEM, TEM, and X-ray diffraction. Single-phase cubic 0.7BaTiO3–0.3BiScO3 solid solutions formed at 600°C. Coatings on Pd using precursors doped with 5 wt% lithium nitrate were dense after sintering at 950°C/1 h. Coatings without lithium nitrate required 1050°C/50 h to densify. Coatings on SrTiO3 heat-treated at 1150°C were dense but formed a (Sc,Ti)-rich second phase.

Synthesis, characterization, and dielectric properties of nanocrystalline Ba1−xPbxZrO3(0 ≤x≤ 0.75) by polymeric citrate precursor route

Abstract

Phase Transition and the Thermal Activated Ordering of the Ions with Pyrochlore Phase in Ln2Zr2O7 (Ln = Sm, Eu)

AbstractTwo series of samples, Sm2Zr2O7 and Eu2Zr2O7, were prepared by the polymeric citrate precursor method and calcined in static air between 700–1450 °C for 24 h. Nano‐size particles obtained were larger with increasing calcination temperatures. Sm2Zr2O7 and Eu2Zr2O7 samples have fluorite phase if they are prepared at temperatures lower than 1000 and 1100 °C, respectively. On the other hand, if the samples are prepared at temperatures higher than 1100 and 1150 °C, they have pyrochlore phase. Phase transition temperature depends on the ionic radius ratio of R(Ln3+)/R(Zr4+). The larger the ratio, the lower the transformation temperature is. Quenched samples have unit cell a‐axis increases with increasing preparation temperatures. The amount of cation antisite in the disordered pyrochlore phase decreases with increasing calcination temperatures. Activation energies calculated on the log (σ;·T) vs. (1/T) for the Sm2Zr2O7 and Eu2Zr2O7 on the cation ordering process are 0.30(1) and 0.39(2) eV, and on the O(3) site are 0.70(9) and 1.2(2) eV, respectively. O2− is much bigger than R3+ so that more energy is required to overcome the hopping potential. Activation energy increases as the ionic radius ratio of the R(Ln3+)/R(Zr3+) decreases due to the decreasing of the unit cell volume.

Preparation and characterization of Nd 2Zr 2O nanocrystals by a polymeric citrate precursor method

Nd 2Zr 2O 7 was prepared by a polymeric citrate precursor method and then calcined at 700–1400 °C in static air. Larger nano-size particles were obtained with increasing calcination temperature. Samples have a defect fluorite phase if they are prepared below 1000 °C. However, if it is heat treated at temperature between 1100 and 1400 °C, a disordered pyrochlore phase is obtained. Unit cell a-axis dimension of the samples gradually increases with increasing preparation temperature. The amount of cation antisite and the occupancy factor of the O(3) site in the pyrochlore phase gradually decrease in the samples prepared at higher temperatures. In other words, the ordering process is an activated behavior. Activation energies of the cation and anion ordering are 0.12(1) and 0.23(2) eV, respectively, equivalent to 12(1) and 22(2) kJ mol −1.

Preparation of ultrathin PZT films by a chemical solution deposition method from a polymeric citrate precursor

Ultrathin PZT film was prepared using a chemical solution deposition method from polymeric citrate precursors. The PZT solution was spin-coated on an amorphous silica layer formed on a Si(1 0 0) substrate. The films were thermally treated from the substrate side with a low heating rate (1°/min) up to 700 °C and finally annealed for 10 h. Ultrathin PZT films without microstructural instability were prepared in spite of high temperature and long annealing time. AFM and HRTEM investigations revealed the formation of a well-developed dense microstructure consisting of spherical crystallites (4–7 nm). Low roughness (2.2 nm) of a ∼26 nm thick layer was obtained for a two-layered PZT film. The grazing incidence X-ray diffraction (GIXRD) measurements confirmed the polycrystalline structure of ultrathin PZT films. Also, GIXRD and electron energy dispersive X-ray (EDS) analysis showed that compositional variations were smaller than expected, in spite of the long annealing time.

Preparation and fluorite–pyrochlore phase transformation in Gd 2Zr 2O 7

Gd 2Zr 2O 7 prepared by a polymeric citrate precursor method has a defect fluorite phase if it is calcined in static air between 700 and 1200 °C; it has a disordered pyrochlore phase, if the sample is heat treated at 1300 or 1400 °C. Phase transformation is accelerated by increasing the preparation temperature and heat treatment period. Sample prepared at 1400 °C is more ordered than the one calcined at 1300 °C. Unit cell a-axis dimension of the pyrochlore phase is slightly longer than the 2 a of the fluorite phase. Expansion of the unit cell is probably due to the different distribution of the oxygen atoms in these two phases and the quenched process. Particle size analysis on the maximum intense XRD peak by the Scherrer formula is in the range of 6–68 nm, grain grows with increasing the preparation temperature and prolonged heat treatment time.

STRUCTURAL AND MAGNETIC PROPERTIES OF (R0.5A0.5)NIO3 PEROVSKITES (R = GD, YB AND A = CE, TH)

Four perovskite compounds with nominal compositions of ( Gd 0.5 Th 0.5) NiO 3, ( Gd 0.5 Ce 0.5) NiO 3, ( Yb 0.5 Th 0.5) NiO 3 and ( Yb 0.5 Ce 0.5) NiO 3 were prepared by a polymeric citrate precursor method. They were either slow-cooled in the furnace or quenched to room temperature. All of them have monoclinic symmetry. Quenched samples have a slightly bigger unit cell volume and longer Ni-O bond length, and a smaller grain size than that of the furnace-cooled compounds. All samples are paramagnetic insulators in the range of 2 K to 300 K. The Th containing compounds have larger tolerance factor and Ni (1)– O (1)– Ni (2) bond angle than that of the Ce containing compounds. No mixed valence of Ce, Th and Ni is observed in these samples.

Nanoparticles of complex metal oxides synthesized using the reverse-micellar and polymeric precursor routes

Current interest in the properties of materials having grains in the nanometer regime has led to the investigation of the size-dependent properties of various dielectric and magnetic materials. We discuss two chemical methods, namely the reverse-micellar route and the polymeric citrate precursor route used to obtain homogeneous and monophasic nanoparticles of several dielectric oxides like BaTiO3, Ba2TiO4, SrTiO3, PbTiO3, PbZrO3 etc. In addition we also discuss the synthesis of some transition metal (Mn and Cu) oxalate nanorods using the reverse-micellar route. These nanorods on decomposition provide a facile route to the synthesis of transition metal oxide nanoparticles. We discuss the size dependence of the dielectric and magnetic properties in some of the above oxides

Polymeric citrate precursor route to the synthesis of nano-sized barium lead titanates

Monophasic oxides of the formula, Ba 1− x Pb x TiO 3 (0≤ x≤1.0) were obtained at temperatures close to 500 °C from polymeric precursors formed using citric acid and ethylene glycol. These oxides were found to be tetragonal for all values of x, the distortion increasing with Pb content. Differential scanning calorimetry (DSC) shows that the decomposition of the precursor to the oxides varies with composition and the decomposition temperature is highest (530 °C) for the x=0.5 composition. X-ray line broadening studies of 900 °C sintered samples show grain size of 50–54 nm in all compositions. TEM studies show agglomerated grains of the size, 40–60 nm. The dielectric constant ( ε) decreases with lead-doping having a value 70 for PbTiO 3. The dielectric loss ( D) for different compositions varied between 0.005 and 0.01 at 100 kHz. The dielectric constant and loss show excellent frequency stability.

Synthesis, characterization and dielectric properties of nanometer-sized barium strontium titanates prepared by the polymeric citrate precursor method

Barium strontium titanate (BST) powders of the formula Ba1 − xSrxTiO3 (0 ≤ x ≤ 1) have been prepared for the first time by the polymeric precursor route using citric acid and ethylene glycol. Pure BSTs were obtained at 500 °C. These oxides were found to have the cubic structure, which is retained even after heating at 800 °C. Detailed X-ray studies on samples sintered at 1100 °C show weak tetragonal distortion for BaTiO3, while the other BSTs retain their cubic structure. The particle size of the sintered oxides increases from 55 nm for BaTiO3 to 88 nm for SrTiO3, from X-ray line-broadening studies. The nano-sized grains are reasonably stable to sintering (the particle size for BaTiO3 changes from 25 nm at 500 °C to 55 nm at 1100 °C). The dielectric constant of the sintered oxides decreases from 510 for BaTiO3 (x = 0) to 190 for SrTiO3 (x = 1) at 100 kHz. The dielectric loss decreases from 0.05 for BaTiO3 to 0.001 for SrTiO3 at 100 kHz. No ferroelectric transition was observed in either the dielectric studies or by differential scanning calorimetry.

Polymeric citrate precursor route to the synthesis of the high dielectric constant oxide, CaCu 3Ti 4O 12

Using citric acid and ethylene glycol, a polymeric precursor of the above compound was obtained at low temperatures (135 °C) which on subsequent heat treatments led to pure CaCu 3Ti 4O 12 at 1000 °C. On sintering further at 1000 °C (20 h), the disks show high density (98%) and the dielectric constant was of the order of 3000 at 1 kHz. The dielectric loss varies between 0.3 and 0.35 (till 100 kHz) beyond that it increases sharply from 0.35 to 0.7 in the frequency range of 100–500 kHz. Our studies on dielectric properties of the above oxide, synthesized by the ceramic method and sintered under the same conditions, led to a dielectric constant of around 2200 at 1 kHz. The dielectric constant decreases with frequency in the oxides obtained by either of the above methods. Scanning electron micrographs (SEM) show much larger grains (nearly spherical) of 2–4 μm in the solid obtained by the ceramic route while the grains were much smaller (0.5–1.0 μm) in the oxide prepared by the polymeric citrate precursor route.

Superconductivity in the triple-perovskite La-Ca-Ba-Cu-O system

Three series of single-phase La-Ca-Ba-Cu-O compounds with tetragonal triple-perovskite structure and respective nominal compositions of La4-xCaxBa3Cu7Oy (LC series, 0.50<or=x<or=1.15), La3CaxBa4-xCu7Oy (CB series, 0<or=x<or=1.25) and La3.5-0.5xCaxBa3.5-0.5xCu7Oy (LCB series, 0<or=x<or=1.25) were prepared by either a solid state reaction method or a polymeric citrate precursor method. All the single-phase materials were superconducting except for samples containing small x in the LCB series. Unit-cell parameters, such as a axes, c axes and cell volume, decreased with increasing Ca substitution. In general, the Tc and hole concentration (p) increased with increasing x from x=0 to x=1.00. In other words, evidence of hole doping was observed during Ca substitution that was the main reason for the increase of the Tc from 0 to 80 K. The optimal Tc was observed in a region close to the formula of La3CaBa3Cu7Oy which had a formula per unit celt of La1.29Ca0.43Ba1.29Cu3Oz where z=7.104, p=0.308, a axis =0.3879 nm and Tc(zero)=80 K.

Preparation and magnetic properties of ultrafine SrFe 12O 19 particles derived from a metal citrate complex

Magnetoplumbite-type strontium ferrite (SrFe 12O 19) powders have been prepared from metal citrate complexes and their magnetic properties have been studied. The optimum pH condition (≈ 6.5) for the formation of metal citrate complexes was predicted through the theoretical consideration of thermodynamic equilibrium constants of the corresponding metal salts in an aqueous solution. Nanometer-sized ferrite particles (≈ 50 nm) could be obtained through the thermal decomposition of polymeric citrate precursor at relatively low temperature (850°C). A large coercive force of 6500 Oe could be obtained, which is one of the highest values reported so far for isotropic SrFe 12O 19 samples and close to the theoretical limit.

Preparation of a single phase Pb 2Sr 0.8La 1.2Cu 2O 6.1+δ superconductor with a citrate precursor method

A single phase Pb 2Sr 0.8La 1.2Cu 2O 6.1+δ superconductor was prepared by a polymeric citrate precursor method. Metal nitrates of the nominal compositions were used as the starting materials. After pyrolysis of the gel-like polymeric citrates, the precursor obtained was calcined at 800 °C for 4 h, sintered at 790 °C for 6 h in the flowing nitrogen atmosphere followed by furnace cooling. The processing period was greatly reduced by this method compared with the conventional solid state reaction method. The chemical titration found that all the Pb ions were in the +2 state and the average copper valence was 1.601 indicating the δ value of 0.101 equivalent to hole concentration of 0.202 in the Cu-O plane of this superconductor.