Citric Gel Method Research Articles

Excellent Red Phosphors of Eu3+ Activated Double Perovskite Structured Series NaSrBi1-xEuxMoO6 (x = 0.0-0.24) Prepared by Citrate-Gel Method

In this work, a double perovskite structured series was prepared by using simple citrate sol-gel method at 700 ºC for 5 h of sintering. The concentrated sample of x = 0.12 exhibits more intensity than all other concentration in their emission spectra for every series. Particle size, thickness of the particle, distance between particles and its surface morphology were identified by scanning electron microscopy. The size and distance between particles in each series lies in between the range of 1 μm-50 nm and 20-50 nm, respectively. Many voids with strong agglomerations were also observed. In addition, the absorption of light capacity for each series investigated through diffuse reflectance spectra method. All the samples of double perovskite structures exhibit a sharp cut-off of absorption light in the UV-visible regions of diffuse reflectance spectra. Predominantly, all the samples shows a very good charge transfer band in their excitation spectra that leads to more absorption of light correspondingly emits high intensity in emission spectra at 395, 464 and 545 nm. All the samples of every series emit main peaks in the range of 550-700 nm in their emission spectra. Out of all four main peaks, 614 nm peak represents the red phosphor with 5D0-7F2 transition in the emission spectra. The prepared double perovskite structure compound CRI coordinates were almost close to commercially available red phosphor i.e. Y2O2S(0.67,0.33) as per NTSC. Hence, the prepared red phosphors can be used in order to display devices, luminescent materials and WLEDs.

Citrate gel synthesis of vanadium diboride

Toward synthesizing vanadium diboride (VB2), mainly mechanochemical and carbothermic routes have been hitherto administired as well as combustion, self-propagating high temperature synthesis (SHS), and solid state metathesismethods. However, methods suggested to date do not deliberately deal with the oxidation state of the vanadium forming the oxide, formation conditions and morphology. Additionally, studies usually suggest an ultimate single reaction, disregarding side reactions. This narrow thermodynamic approach lacks key information in regards to the required conditions. Herein, this study reports the laboratory scale synthesis of VB2 nanopowders employing citrate gel method. The process is carried out using ammonium metavanadate (NH4VO3) as the vanadium source, boric acid (H3BO3) as the boron source, and citric acid (C6H8O7) as a chelating agent. Raw powder chelate is subjected to boro/carbothermic reactions under argon atmosphere in the range of 1100–1500 °C correlated with thermodynamic calculations with a 100 °C interval which are in good agreement with the experimental data. The resulting material is characterized to be at least 92% VB2 within the possibility of excessive graphitic carbon, carbon deficient vanadium carbide (V8C7) and/or non-stoichiometric VxBy(yx≤32) remaining as impurities. The formation mechanisms referring Liquid-Solid (LS) and Vapour-Solid (VS) reaction pathways throughout the major steps are described.

Hysteresis Energy Loss of Nanocrystalline CoFe2O4 Synthesized by Modified Citrate-Gel Method

Hysteresis Energy Loss of Nanocrystalline CoFe2O4 Synthesized by Modified Citrate-Gel Method

Ferroelectric-Ferromagnetic Heterostructures based on Sodium Substituted Lanthanum Manganite Thin films deposited on PMN-PT substrate by Pulsed Laser Deposition

Phase pure targets of sodium substituted lanthanum manganites (LNMO) were prepared by citrate gel method and characterized. These targets were laser ablated by pulsed laser deposition technique and were deposited simultaneously on silicon and relaxor ferroelectric PMN-PT substrates with a view to fabricating ferroelectric-ferromagnetic 2D heterostructures. Magnetization measurements reveal a higher magnetization for films of 100 nm thickness than the 300 nm thick films. The PMN-PT substrate influences the magnetic properties of sodium substituted lanthanum manganite thin films. The strain effects are higher for 100 nm thin films. The saturated polarization-electric field (P-E) loop measurements carried out on films demonstrated that, there is a considerable change in hysteresis parameters (coercivity and remanent polarization) upon thin film deposition. PMN-PT LNMO thin films can be viewed as a heterostructure where ferromagnetism and ferroelectricity co-exist and has potential applications in magnetoelectrics.

Low-temperature magnetic properties of erbium doped bismuth nano-ferrites

Nanocrystalline pure and erbium (Er3+)-substituted bismuth ferrite nanoparticles were synthesized by the citrate-gel auto-combustion method. Prepared powders were sintered at 500 °C for five hours in the air and characterized by XRD, TEM, and HR-TEM. X-ray diffraction (XRD) analysis showed the distorted rhombohedral structure of the ferrites. The surface morphology and particle size of the samples were observed by high-resolution transmission electron microscopy. The lattice parameter, crystalline size, X-ray density has been calculated from d-spacing. The perceived results can be explained depending on doping concentration. The temperature dependence of magnetic properties of Bi-Er nanoparticles was carried out by using a vibrating sample magnetometer (VSM). The magnetization as a function of applied field at ± 100 Oe was carried out at 3 and 300 K. Zero-field-cooled and (ZFC) and field-cooled (FC) magnetization measurements under an applied field of 100 Oe in the temperature range of 3-360 K. These measurements give the results of blocking temperature (Tb) at around 350 K.

New insights on photocatalytic hydrogen evolution of ZnFe2−xGaxO4 (0 ≤ x ≤ 2) solid solutions: Role of oxygen vacancy and ZnO segregated phase

The exponential increase in global energy and clean energy demands lead to the necessity for development of efficient photocatalyst for hydrogen evolution. Herein, photocatalytic hydrogen evolution activity with nano-structured ZnFe2-xGaxO4 (0 ≤x ≤ 2) solid solution samples synthesized by citrate-gel method at 550 °C is reported. The prepared materials have been characterized for their structure and optical properties. The formation of solid solution with spinel type structure in the complete range of composition and a systematically decreasing trend of unit cell parameters with increasing Ga3+ concentration is observed from powder XRD studies. The band gap of these solid solutions could be tuned from 1.9 to 3.1 eV by increasing the Ga3+ concentration. Without any co-catalyst, ZnFe2O4 shows poor catalytic activity (378μmolh−1g−1) for photocatalytic hydrogen evolution from water. Whereas its activity enhances with loading of co-catalyst and touches a maximum activity of 3089μmolh−1g−1 with loading 1 wt% of Pt. The catalytic activity increases systematically with increasing Ga concentration in the solid solutions and reaches to 3989μmolh−1g−1 for ZnGa2O4 nanomaterials. Electrochemical impedance spectroscopic and transient photocurrent measurements also support the observed increasing trend. The lower catalytic activity of ZnFe2O4 has been attributed to the faster e-h recombination due to lower band gap and inherent oxygen vacancies. A smaller amount of oxygen vacancies and segregated ZnO phase observed in Ga substituted ZnFe2O4 samples favor the e-h pair separation and that facilitate the hydrogen generation from water.

FTIR, Optical, Electrical and Magnetic Properties of Sm3+ Doped Mg Nano Ferrites

Synthesized Sm, doped Mg nano ferrites with composition MgSmxFe2-xO4 (x = 0,0.025, 0.050, 0.075, 0.100) using the technique of citrate-gel auto-combustion method were analyzed through various experimental techniques. XRD analysis confirmed single-phase cubic spinel structure, while FTIR spectroscopic analysis displayed two absorption peaks that are characteristic of spinel nano ferrites. UV-visible spectral analysis was carried out to study the optical absorption behavior of the prepared ferrites. Two probe method was used to study the dc electrical resistivities of Sm doped Mg nanoferrites between 200 °C–500 °C. A plot between log (σT) vs. inverse temperature yields a curve that reveals prepared nano ferrites' semiconducting nature. A study of TEP (Thermo Electric Power) for prepared samples was carried out at a high temperature (573K). Seebeck coefficient and Curie Temperature of Sm doped Mg nanoferrites were observed. Measurements of magnetization were done by using VSM (Vibrating Sample Magnetometer).

Dependence of oxygen desorption kinetics on processing methods of SrCoO2.5

The effect of processing methods on oxygen storage and exchange kinetics of brownmillerite (BM) SrCoO2.5 is compared in terms of their reversible oxygen incorporation and desorption kinetics. BM SrCoO2.5 was synthesized through two different methods; solid-state synthesis and the nitrate–citrate gel method, both followed by Al foil pad quenching. Oxygen storage characteristics of synthesized samples were analysed using a home-built volumetric set-up. The maximum oxygenation achievable for BM SrCoO2.5 under prevailing conditions of O2 partial pressure (16 bar O2), temperature (673 K) and time (1 h) was unaltered, regardless of the synthesis method. Oxygen exchange kinetics of desorption was faster in the nitrate–citrate synthesized sample than in the solid-state synthesized sample. The kinetics of desorption correlated with the crystallite and particle sizes of the samples. The mechanism of desorption follows nucleation and growth model for nitrate–citrate synthesized sample, while it follows contracting sphere model for solid-state synthesized sample.

The effect of shell layer on magnetic, transport, and electrochemical properties of La0.7Sr0.3MnO3 nanoparticles

LSMO nanoparticles with core-shell structure have been synthesized by the non-aqueous sol-gel method and for comparison of their structural, magnetic, transport, and electrochemical properties, the non-core-shell LSMO nanoparticles have been synthesized by citrate gel method. The structural analysis confirms the formation of LSMO core-shell nanostructure with a ~2.3 nm shell layer and non-core-shell LSMO nanoparticle. The magnetic properties of LSMO-CS are explained in terms of the exchange interaction between the core and the disordered surface layer of the nanoparticles. The transport properties are examined with the help of different conduction mechanisms involved in different temperature regions. The low field magnetoresistance (LFMR) and electrochemical properties of the LSMO-CS are improved as compared to the LSMO-NCS nanoparticles.

Irregularly Shaped Mn2O3 Nanostructures with High Surface Area for Water Oxidation

Water oxidation is an energy-consuming, four-electron-transfer reaction and is essential for solar fuel production from water. Catalysts based on precious metals such as RuO2 and IrO2 show high efficiency for oxygen evolution reaction. However, these catalysts are less abundant and expensive. To date, earth-abundant water oxidation catalysts still exhibit less activity for water oxidation. Herein, we report the synthesis of high surface area Mn2O3 nanomaterials for an efficient photocatalytic water oxidation catalyst. The synthesis process involves three simple steps. In the first step, CaMnO3 is synthesized by the citrate-gel method. In the second step, CaMnO3 is transformed into freestanding layers of ε-MnO2 by selective removal of Ca2+. In the third step, these layers are converted into irregularly shaped two-dimensional Mn2O3 flakes (AD-Mn2O3) by calcination at 550 °C. These AD-Mn2O3 nanostructures show 4 times higher surface area (127 m2 g–1) when compared to the irregularly shaped Mn2O3 nanoparticles (CG-Mn2O3) synthesized by the citrate-gel method at the same temperature. The AD-Mn2O3 nanostructures show super hydrophilicity with a contact angle of zero degree. This material exhibits excellent photocatalytic water oxidation activity with a turnover frequency of 1.53 × 10–3 s–1, which is twice the activity shown by CG-Mn2O3. This study can help in developing an earth-abundant, cost-effective, efficient catalyst for overall water splitting.

Effect of Al Doping on Magnetic Properties of Co-Mn Nanoferrites Synthesized via Citrate-Gel Method

The structural and magnetic properties of aluminium substituted Co-Mn nanoferrites synthesized via a chemical route viz. citrate-gel autocombustion method have been reported. Aluminium content has been varied from x=0 to x=1 with an increment of 0.2 in Co0.75Mn0.25AlxFe2-xO4. The structural confirmation was done with the basic characterization techniques such as XRD study, FTIR spectroscopic and the surface morphology was examined using SEM and EDX spectroscopic analysis. To study the optical absorption behaviour of the prepared ferrites, UV-visible spectral analysis was carried out. XRD analysis established the formation of cubic spinel structure of the materials with the average crystallite size of 15.5 nm to 19.94 nm. FTIR spectra has shown two absorption peaks that are characteristic of spinel nano ferrites. From the UV-visible spectral data, energy band gap (Eg) values were evaluated. The data witnessed an increase in the Eg value of the ferrite by doping of Al3+ ion into the ferrite. Room temperature magnetization measurements were carried out before and after aluminium doping in the samples using vibrating sample magnetometer. It was revealed that the substitution of aluminium in the lattice has modified the material into a soft magnetic material. Consequently, they find applications in transformer and motor cores.

Structural, Optical, Ferroelectric and Magnetic Properties of NiTiO3 Ceramic Synthesized by Citrate Gel Method

The NiTiO3 ceramic was synthesized in nanostructured form by citrate gel method. The phase structure, microstructure and magnetic properties of synthesized compounds were investigated by X-ray diffraction (XRD), scanning electron microscope and vibrating sample magnetometer. Williamson–Hall plot was used to calculate the crystallite size and microstrain of sample. The XRD analysis showed the formation of rhombohedral crystal structure of synthesized powders. The crystallite size is about 35[Formula: see text]nm and microstrain is [Formula: see text]. The optical band gap was estimated from UV-Visible spectrum with value of 2.43[Formula: see text]eV. The NiTiO3 samples showed coexistence of ferroelectric and antiferromagnetic properties at room temperature.

High entropy phase evolution and fine structure of five component oxide (Mg, Co, Ni, Cu, Zn)O by citrate gel method

(Mg, Co, Ni, Cu, Zn)O is an equiatomic five-component high entropy oxide (HEO), which has shown promising dielectric and intercalating properties. We report the synthesis of a phase-pure (Mg, Co, Cu, Ni, Zn)O HEO by the citrate-gel auto-combustion method and the crystallographic phase evolution as a function of annealing temperature. The powders as-synthesized by auto-combustion at 230 °C had ~85% high entropy rocksalt phase along with tenorite (CuO) and wurtzite (ZnO) phases. On annealing at the temperatures between 600 and 700 °C, the fraction of unary oxide phases ZnO, CuO, and Co3O4 (spinel) increased. On annealing at higher temperatures, the unary oxide phases dissolved, and finally, at annealing temperatures greater than 850 °C, a phase pure high entropy solid solution having rocksalt structure was obtained. All the metal ions were in +2 state, as observed from the XANES spectra. EXAFS revealed the presence of Jahn-Teller distortion in CuO6 octahedra. The structural parameters derived from EXAFS were in close agreement to that obtained from XRD measurements.

Effect of copper dopant on microstructural and optical properties of NiTiO3 ilmenite materials synthesized by citrate method

In this work, the Ni1-xCuxTiO3 (0 ≤x ≤ 0.1) ilmenite materials were successfully synthesized using the citrate-gel method using nickel nitrate, copper nitrate and titanium (IV) isopropoxide as Ni, Cu, Ti sources and citric acid as complexing reagent. The evolution of the microstructural properties was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Powder X-ray diffraction pattern confirms the formation of the ilmenite phase for all the samples. The particle size of the prepared samples substantially increased with increase of copper dopant content. The study of phonon vibration by Raman spectroscopy identified a change in structure of NiTiO3 due to Cu dopant. The optical properties with the Cu content was carried out using UV-vis absorption spectroscopy. The reduction of optical band gap from 2.31 eV to 1.99 eV was obtained for undoped NiTiO3 and 10 mol.% Cu dopant in NiTiO3, respectively. To evaluate the photocatalyst properties of NiTiO3, the photocatalytic degradation of congo red under visible light irradiation was carried out. Our results revealed that the copper dopant into NiTiO3 lattice promoted the increase of particle size, decrease of optical bandgap and enhancement of textile photodegradation.

Structural, Magnetic and DC Electrical Resistivity Studies of Ni–Zn–Cr Ferrites Prepared by the Citrate-Gel Auto-Combustion Method

Nanocrystalline chromium substituted Ni–Zn nanoferrites with composition Ni0.5Zn0.5CrxFe2−xO4 (0 ≤ x ≤ 0.25, in steps of 0.05) have been synthesized using citrate-gel auto-combustion method. The as synthesized powder of the starting composition has been characterized by using TG–DTA in air atmosphere for the temperature up to 800 °C and X-ray diffraction for its structure. Upon confirming the spinel phase for the starting composition, the chromium substituted Ni–Zn ferrite nano powders were synthesized by the similar procedure. The as synthesized powders were pressed into pellets and toroids under uniaxial pressure followed with sintering in air atmosphere for 4 h at 1100 °C for electrical and magnetic characterizations. The X-ray diffraction studies revealed a decrease of the lattice constant and considerable modification in the structure of Ni–Zn ferrite with the substitution of Cr3+ for Fe3+ ions. The room temperature FT-IR spectra displayed three significant IR absorption bands in the wave number range of 350–600 cm−1 which is a characteristic of the spinel structure. The band positions and intensities were found to vary with chromium substitution in Ni–Zn ferrite. The room temperature DC electrical resistivity and activation energy for conduction in the Ni–Zn–Cr ferrite samples were measured by using the two-probe method while the AC resistivity studies were carried out in the frequency range of 1 kHz to 13 MHz and the all the observations have been discussed in the light of existing understanding.

Enhancement of electrical properties Ce0.8Sm0.2−xO2−δ by Sr2+ doping

Nanocrystalline strontium co-doped Samarium Doped Ceria samples with different compositions Ce0.8Sm0.2−xSrxO2−δ (x = 0.05, 0.1, 0.15, 0.2) prepared by the citrate gel method. X-ray diffraction tools confirm the structure of the system. Field Emission Scanning Electron Microscopy images detail the microstructure of the sintered pellets grain and grain boundaries. The elemental content of the compositions confirmed by Energy Dispersive Spectroscopy analysis. The presence of concentrated O2- vacancies in the strontium co-doped Samarium Doped Ceria samples analyzed from the Raman Spectroscopy. Electrical properties of the sintered pellets are analyzed in terms of ac data from ac complex impedance spectroscopy. Normalization of modulus spectra of the prepared samples shows the low value of stretching factor (β) less than 1, which indicates a non-Debye relaxation process. The Arrhenius plots for all compositions show as the temperature increases; there is an increase in the value of conductivity, which indicates that the prepared samples follow a negative temperature coefficient of resistance. The combined analysis of impedance, modulus, and electrical conductivity attains value suitable for solid oxide fuel cell applications. Among the different compositions, Ce0.8Sm0.05Sr0.15O2−δ samples exhibit a maximum conductivity of 3.39 × 10−4 Scm−1 at 750 °C.

Thermoelectric Power, Electrical Resistivity and Magnetic Properties of Ni-Sm Nano-particles

Nanocrystalline Samarium doped Nickel ferrites having compositional formula NiSmXFe2-XO4 (0.00≤X≥0.10) were prepared by the citrate-gel auto combustion method and sintered at 5000C. The structural characteristics such as XRD analysis were shown cubic spinel structure, and the structural parameters like lattice parameter, X-ray density, bulk density, and porosity variations with Sm doping were studied. The surface morphology of prepared samples was observed by Scanning Electron Microscopy (SEM). The magnetic parameters were studied at room temperature with VSM, and the observed results are discussed with composition. The DC electrical properties were studied using a two-probe method in the temperature range from room temperature to well beyond Curie temperature. Thermoelectric power studies were carried out from room temperature to well beyond transition temperature with a differential method. The Seebeck coefficient variation with temperature was studied, and it shows the prepared samples are classified as n-type semiconductors. The observed results can be explained on the basis of the conduction mechanism.

Processing and characterization of Ba0.5Sr0.5Fe12O19/Y3Fe5O12 nanocomposite ferrites towards permanent magnet applications

A one-step citrate-gel combustion method was employed to process (Ba0.5Sr0.5Fe12O19)1-x/(Y3Fe5O12)x nanocomposite ferrites with different compositions (x = 0.1, 0.2, 0.3, and 0.4). The morphological, structural, thermal, and magnetic properties of the as-synthesized samples were investigated with respect to their structural, thermal, and magnetic properties using field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and vibration sample magnetometer (VSM), respectively. The FESEM micrographs revealed homogeneous distribution of hard and soft magnetic phases throughout the sample. The XRD results confirmed the crystallization of both BSFO and YIG as hard and soft magnetic phases, respectively, without any other secondary phases. The TGA/DSC curve confirmed the phase formation of the nanocomposite material around 1100 °C with a total weight loss of ~ 63%. The magnetic hysteresis loops of as-synthesized ferrite nanocomposites demonstrated a single-phase behavior due to the existence of strong inter-grain exchange coupling between the hard and soft magnetic phases. The single peak in switching field distribution (SFD) curves of synthesized nanocomposite ferrite were observed for all the compositions. Maximum values of coercivity (6090 Oe), saturation magnetization (54 emu/g), and energy product (19.5 kJ/m3) were achieved for the BSFO0.9/YIG0.1 composition. The results of the present study suggest that the magnetic parameters such as those derived from the nanocomposite ferrites are superior as compared with that of those obtained for the constituent YIG and BSFO phases.

Tailoring La0.8Sr0.2MnO3/La/Sr nanocomposite using a novel complementary method as well as dissecting its microwave, shielding, optical, and magnetic characteristics

In this work, a novel approach was introduced to reduce the oxide nanoparticles and extract the pure metal from them. Accordingly, La0.8Sr0.2MnO3 nanoparticles were prepared through the conventional citrate gel method, and then they were reduced using a solvothermal method by ethylene glycol as a reductive agent. Chemical species, magnetic parameters, crystal structures, and morphological properties of the fabricated structures were deeply studied by Fourier transform infrared (FT-IR), vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FE-SEM) analyses, respectively. Noticeably, the curves of the diffuse reflection spectroscopy (DRS) suggested a lower energy gap for the La0.8Sr0.2MnO3/La/Sr nanocomposite. Finally, the microwave absorbing characteristics of the specimens were scrupulously investigated using the polystyrene (PS) and polyvinylidene fluoride (PVDF) media. It was found that La0.8Sr0.2MnO3/La/Sr blended in PVDF gained a remarkable reflection loss of 94.68 dB at 15.31 GHz with an only thickness of 1.75 mm, meanwhile displaying an efficient bandwidth as wide as 6.74 GHz (reflection loss (RL) > 10 dB). Noteworthy, La0.8Sr0.2MnO3/PS illustrated a considerable efficient bandwidth of 2.36 GHz (RL > 20 dB). Moreover, La0.8Sr0.2MnO3 composites demonstrated more than 88% electromagnetic interference shielding efficiency (SE) along the X and Ku-band frequency.

Effect of carbonization temperature on the lithium storage performances of porous Sb/C nanocomposite

In the present study, Sb/C nanocomposites have been synthesized using citrate-gel method in combination with a carbonization process at different temperatures in N2 gas. At reasonable carbonization temperatures, the porous Sb/C nanocomposites with novel foam like-interconnected three-dimensional structure, which is built-up by nanosized Sb particles covered by a carbon shell, are obtained. Among the synthesized composites, the Sb/C-600 sample, which is calcinated at 600 oC, exhibit the best lithium storage. At a discharge-charge rate of 0.1 C, the Sb/C-600 electrode can supply an initial reversible specific capacity of 640.7 mA h g-1, 1.7 times higher than the theoretical specific capacity of graphite anode. During 100 cycles, the electrode shows a slight capacity decay with 0.0348% of loss capacity per cycle. Because of this featured architecture, the Sb/C nanocomposites severe as anode material with enhanced lithium storage performances for rechargeable lithium ion batteries.