Citrate Gel Route Research Articles

Consistency between theoretical conduction models and experimental conductivity measurements of strontium-doped lanthanum manganite

La0.9Sr0.1MnO3 nanoparticles are elaborated using the citrate-gel route. The X-ray patterns show that the prepared sample crystallizes in the rhombohedral symmetry. Interesting results were obtained from the electrical conductivity measurements of the lanthanum manganite doped low strontium content. Indeed, numerous conduction models are used to analyze the electrical conductivity response. It is found that transport properties are governed by hopping processes at different temperature ranges. Such mechanisms explain the evolution of the DC-conductivity as well as the displacement of charge-carriers with temperature excitation. Then, thermal activation of the charge-carriers is confirmed. The temperature dependence of the frequency exponents reveals the contribution of Non-overlapping Small Polaron Tunneling (NSPT), Quantum Mechanical Tunneling (QMT), Over-lapping Large Polaron Tunneling (OLPT) and Correlated Barrier Hopping (CBH) to the transport properties. Conductivity spectrum shows a significant increase with frequency in the temperature range [80–500 K]. The frequency dependence of the AC-conductivity obeys to the "Double Jonscher Power Law" in the temperature range [80–300 K]. From 340 to 500 K, it is governed by the "Single Jonscher Power Law". Moreover, a high frequency plateau is observed presenting a percolation behavior in the conductivity spectrum. The deduced values of the disorder and hopping energies show the impact of hopping distance and polaron radius on the charge-carriers transport.

Impact of Sintering Temperature on the Electrical Properties of La0.9Sr0.1MnO3 Manganite

La0.9Sr0.1MnO3 nanoparticles were prepared using the citrate–gel route and sintered at different temperatures (TS = 600 °C, 800 °C, and 1000 °C). The x-day diffraction patterns reveal that the samples exhibit a single phase with a rhombohedral (R3¯C) structure. The transmission electron microscopy technique shows an increase in the grain size when the sintering temperature (TS) rises. The obtained values are approximately similar to that of crystallite size calculated from x-ray diffraction patterns. The impact of sintering temperature (TS) on the electrical properties of La0.9Sr0.1MnO3manganite is examined using the impedance spectroscopy technique. A metal-semi-conductor transition at a specific temperature (TM-SC) is observed for all samples. Indeed, the sintering temperature increase induces the shift of this transition temperature toward higher temperatures. Such a behavior is explained by the increase in the grain size. An agreement between the metal-semi-conductor transition values coming from the DC resistivity and the grain boundaries analyses is observed. This agreement proves the contribution of the grain boundaries in the electrical properties of the studied samples. In addition, the presence of the relaxation phenomenon is confirmed. The fitted Nyquist plots show the correlation between the microstructure of the material and the electrical properties using an electrical equivalent circuit model. The DC resistivity and the impedance analyses reveal the thermal activation of the transport properties in the investigated system.

The crystal chemistry and electrical properties of Fe doped Ca12Al14O33 (Mayenite)


 
 
 X-ray and neutron powder diffraction have been used to study the crystal chemistry of Fe doped mayenite (Ca12Al14-xFexO33). Solid- state synthesis was used to prepare Ca12Al14-xFexO33 where x = 0, 0.1, 0.2, 0.5 and 0.6 and the citrate gel route was used to prepare Ca12Al14-xFexO33 where x = 0, 0.05, 0.1, 0.2, 0.3 and 0.4. X-ray powder diffraction data indicate that samples with the same composition but synthesized by the citrate gel route were more likely to be phase pure than samples obtained by traditional solid-state synthesis. The refined lattice parameters were observed to increase with increasing Fe concentration, irrespective of the synthesis method. Refined neutron powder data confirm that Fe is going into Al site rather than Ca site. A 2-point probe was used to measure the electrical properties of the Fe doped citrate gel synthesized samples and showed that the resistivity increases for the Fe doped samples compared to the undoped mayenite.
 
 

Dependence on charge transfer band and emission properties by the crystal chemistry of A- and B-site cations in Eu3+-doped quaternary pyrochlore-type red phosphors Ca(RE)1−x(M)NbO7 (RE = Y, Gd; M = Ti, Sn)

Dependence on charge transfer (CT) band and emission properties are investigated in Eu3+ doped quaternary pyrochlore-type oxides,Ca(RE)1−x(M)NbO7 (RE = Y, Gd; M = Ti, Sn) by varying the crystal chemistry of A- and B-cations. The CT band is shallow and extending to higher wavelength in highly covalent environment of Eu3+ in CaYTiNbO7 resulting in improved Eu3+ excitation levels. Contrary to this, the CT band is positioned at a lower wavelength and intense in highly polarizable environment of Eu3+ in CaGdSnNbO7 leading to poor energy transfer to Eu3+ excitation levels. Consequently, CaY0.85TiNbO7:0.15Eu3+ exhibited intense narrow red emission (fwhm3.4 nm) with high asymmetric ratio 8. Further, the phosphors CaY0.85TiNbO7:0.15Eu3+ prepared through citrate-gel route show high quantum efficiency (74%) and sharper red emission (fwhm3.2 nm) with intensity values 8 times better than the solid state one and comparable to the commercial Y2O3:Eu3+ red phosphor. Thus, these phosphors are potential candidates for pc-WLEDs applications.

Significantly suppressed leakage current and reduced band gap of BiFeO3 through Ba–Zr Co-Substitution: Structural, optical, electrical and magnetic study

Bismuth Ferrite (BFO), Ba substituted BFO (BBFO) and Ba–Zr co-substituted BFO (BBFZO) nanoparticles have been synthesized via citrate-gel route. The common problem of BFO i.e; compositional instability, low magnetization and high leakage current was resolved by this doping technique. Remanent magnetization and remanent polarization improved significantly for BBFZO sample compared to that of BFO. Structural, optical and improved dielectric properties were also investigated. Structural study confirmed the enhanced structural distortion in BFO due to doping of Ba and Ba–Zr ions. The calculated energy band gap has been reduced to 1.52 eV for BBFZO nanoparticles from a value of 2.55 eV for BFO. Leakage current was suppressed by almost seven orders of magnitude for Ba–Zr co-substituted bulk BFO compared to that of undoped BFO. Morphological study of bulk samples has shown gradual reduction in grain size upon Ba doping and Ba–Zr co-doping in BFO, respectively.

Magnetic Properties of Cu2+ Substituted Ni–Zn Nano-Crystalline Ferrites Synthesized in Citrate-Gel Route

The Nano-crystalline divalent copper ion substituted Ni–Zn ferrites having chemical formula Ni0.5Zn0.5−xCuxFe2O4 (where x = 0.05 to 0.25 in steps of 0.05) were prepared by citrate gel auto-combustion method. The X-ray diffraction study confirmed the single phase spinel cubic structure and the crystallographic studies indicate that the lattice parameter was observed to be decreased with increasing of Cu2+ concentration. Scanning Electron Microscopy was conducted to observe surface morphology and grain size/shape. Magnetic measurements were carried out using Vibrating Sample Magnetometer for magnetization and Impedance analyzer for permeability up to 15 MHz. Magnetization studies revealed that the incorporation of copper into the system modified the exchange interactions leading to gradual decrease in saturation magnetization. Highest saturation magnetization was observed for the base composition Ni0.5Zn0.5CuFe2O4 with 61 emu/g. There was an increase in coercivity and remanence with copper concentration. Frequency and temperature variation of inductance measurements were performed to understand the system behaviour at different threshold limits. Enhancement of initial permeability was observed up to the concentration x = 0.15 and its variation is observed to be grain size dependent. Temperature variation of permeability leads to Curie temperature, which was increased with increasing of Cu2+ concentration. All magnetic characteristics of the present system of nano crystalline ferrites displayed interesting deviations and reasons were well justified.

Magnetic and heating aptitudes of PEG coated [formula omitted] and [formula omitted] mediators towards hyperthermia methodology

In the present study functionalized mediator of Lanthanum strontium manganite (LSMO) has been investigated for magnetic fluid hyperthermia (MFH) applications. Perovskite structured (La1−xSrxMnO3) employing two Sr concentrations (x = 0.27 & 0.33) were attempted to coat with long chain structured polymer named Polyethylene glycol (PEG- 6000 g/mol) by adopting novel concentrations (5% & 14% w/v) in order to assess a detailed comparison of the effect of concentration of same coating material on two different LSMO's series. The Citrate-gel route was adopted to synthesize LSMOs nanoparticles (NPs). XRD revealed the super-paramagnetic (SPM) nature of synthesized NPs showing an approximate crystallite size of ∼17 nm. The LSMOs tailored with PEG showed an effective bonding of polymer with NPs exhibited by FTIR spectra. The magnetic parameters of coated NPs subjected to VSM at room temperature displayed an appreciable saturation magnetization and very slight coercivity owing to their SPM behaviour. During each synthesis, the relative proportions of polymer attached to LSMOs were evaluated through TGA analysis accompanied by DTA studies showing successive decomposition processes. The induction heating behaviours of NPs under an external radio frequency field displayed quite an appreciable approach for required Hyperthermia efficacy in the required range of 40–60 °C. Besides this, the coated NPs were dispersed in normal saline as an innovative try forming a ferro-fluid (∼19 mg/ml) and showed considerable approach towards induction heating for the destruction of cancerous cells employing hyperthermia methodology.

Effect of B-site doping on electrical conductivity of YAlO3 based electrolytes for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) have emerged as high temperature fuel cell technology operating at temperatures around 1000 °C. Lowering the operating temperature enables the use of cheaper materials while maintaining high power outputs. Electrolytes with ABO3-type perovskite structure are good ionic conductors and are promising materials for SOFCs. In this study, a systematic investigation on the synthesis and characterization of Mg- substituted YAlO3 system has been performed. The samples have been synthesized by wet chemical citrate gel route and the electrical conductivity measurements have been conducted in air between 300 and 800 °C. Effect of composition of the phases on total conductivity has been analyzed employing X-ray diffraction. The influence of microstructure on total conductivity has been studied using scanning electron microscopy and orientation imaging microscopy.

Magnetic and heating properties of [formula omitted] (x = 0.27 & 0.33) mediators coated by Sodium Oleate for magnetic fluid Hyperthermia applications

Perovskite Lanthanum strontium manganite (LSMO) has been analyzed as a proficient hyperthermia mediator for a couple of decades. In the present study (La1−xSrxMnO3) with Sr concentration (x = 0.27 & 0.33) are coated with biocompatible polymer Sodium Oleate (SO). SO coating is done by adopting novel routes. One of them has been applied for ferrites formerly and is being successfully done with LSMOs in the present task. The other methods of coating are done by choosing different concentrations of the polymer as well as adjusting different parameters related to it. The objective is to evaluate a detailed comparative study of two different LSMOs’ series with the same coating polymer in order to understand their Hyperthermia efficacy. LSMOs are synthesized by Citrate-gel route having an approximate size of ∼17 nm as revealed by XRD and after surface functionalization with the polymer, are characterized by a number of analytical procedures to examine their different properties. The polymers reveal an efficient surface attachment with NPs as disclosed by FTIR. The coated NPs exhibit very narrow hysteresis loop and appreciable saturation magnetization at room temperature when subjected to VSM. TGA and DTA analysis show relative amounts of polymer bonded to the LSMOs surface and subsequent decomposition mechanisms. The magnetic induction heating studies by employing radio frequency alternating field display adequate response of these prepared NPs in Hyperthermia range (40–60 °C). These coated NPs show an appreciable approach towards efficient induction heating when dispersed in normal Saline for the first time as a carrier medium proving to be an effective ferrofluid.

Influence of morphology on luminescence properties of xenotime-type phosphors NaYP2O7:Eu3+ synthesized via solid state and citrate-gel routes

A series of Eu3+ activated xenotime type rare earth phosphate NaYP2O7 based orange–red emitting phosphors have been prepared via solid state (SS) and citrate gel (CG) methods. The morphological variation of the developed phosphors concerning synthesis method and heat treatment has significantly influenced the luminescence properties. The phosphors synthesized by the CG route reveals the formation of homogeneous powder with small particles along with uniform size. The developed phosphors exhibit intense orange–red emission under 394 nm near UV excitation with a full width half maximum ~ 2 nm. Compared with the phosphors synthesized by SS route, the phosphors obtained by CG method possess enhanced and sharper orange–red emission with longer lifetimes due to the 5D0–7F1–2 transitions. The developed narrow red emitting phosphors have better emission intensity in comparison with commercially available Y2O3:Eu3+ red phosphors. Thus, these phosphors could be a suitable candidate for solid state lighting applications for the fabrication of white light emitting diodes.

Facile Synthesis of Ceria Based Ceramic Nanorods by Citrate gel route

Facile Synthesis of Ceria Based Ceramic Nanorods by Citrate gel route

Stability and coloring properties of Ni-qandilite green spinels (Ni,Mg)2TiO4: The “half color wheel” of Ni-doped magnesium titanates

Solid solutions of Ni-doped qandilite spinel (Mg2−xNixTiO4, x = 0–0.4) prepared by solid-state and citrate-gel routes were investigated as potential ceramic pigments or dyes. Fired powders were characterized by conventional solid-state and color-measurement techniques. The increase of Ni-doping favored qandilite decomposition in Ni-geikielite (Ni,Mg)TiO3 and Ni-periclase (Ni,Mg)O. In the ceramic route, Ni-doped qandilite was stabilized at 1400 °C, but still accompanied by small amounts of MgTiO3 and MgO. Remarkably, the citrate-gel route enabled the formation of single-phase qandilite already at 1200 °C (up to 10%mol Ni), and at 1400 °C for all amounts of Ni-doping. Ni-doped qandilite developed green colors due to Ni2+ ions allocated exclusively in octahedral sites of qandilite spinel, being the green colors of higher chroma in citrate-gel powders. Ni-qandilite powders were chemically instable in low-temperature (950–1050 °C) ceramic glazes, acting only as yellow ceramic dyes. Optical properties of Ni-doped karrooite, geikielite and qandilite pigments were compared.

Synthesis and coloring performance of Ni-geikielite (Ni,Mg)TiO3 yellow pigments: Effect of temperature, Ni-doping and synthesis method

Solid solutions of Ni in MgTiO3 ilmenite (geikielite) were investigated as potential yellowish ceramic pigments or dyes. Ni-geikielite samples (Mg1−xNixTiO3, x=0–0.4) were prepared by solid-state and citrate-gel routes and fired pigments were characterized by XRD, SEM/EDX, UV–vis–NIR and color measurement techniques. The increase of Ni-doping enhanced ilmenite stabilization in ceramic samples, obtaining almost single phase of Ni-geikielite for x=0.4 at 1200 and 1400°C. Fired pigments exhibited intense yellow colors at both temperatures, associated to Ni2+ ions in distorted octahedral A sites of ATiO3 ilmenite, and an increase of the orange hue with firing temperature arising from an enhanced (Mg,Ni)O6 polyhedral distortion. Noteworthy, citrate-gel samples exhibited a much higher reactivity, yielding well-crystallized Ni-geikielite at lower temperatures (800°C/3h), and leading to higher chroma yellow-orange colors even at lower Ni loadings. These pigments were partially stable in commercial low-temperature ceramic glazes, giving rise to weaker yellowish colors irrespective of the preparation route.

Effect on structural and magnetic properties of aluminum substitutedNi–Znnanoferrite system prepared via citrate-gel route

Nickel zinc aluminum nanoferrites with general formula Ni0.5Zn0.5Fe2-xAlxO4(x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25) were prepared by citrate-gel autocombustion method and heat treated in air at 1100°C for 4 h. The crystallography, surface morphology and magnetic properties were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure and absence of any secondary phases. The crystallite size estimated from Scherrer formula for the Gaussian peak (311) has been found to be around 30 nm. The results obtained show that with Al3+doping, the lattice parameter decreases due to smaller ionic radii of Al3+ions replaces larger Fe3+ions. The distribution of Al3+ions over tetrahedral (A) and octahedral (B) sites is estimated from X-ray intensity calculations. The arrangement of magnetic ions among the tetrahedral and octahedral sites due to the substitution of Al3+ions modifies the saturation magnetization (Ms) and coercivity (Hc). The room temperature magnetization values increases up to x = 0.1 and then decreases for the increase in aluminum concentration above x > 0.1. Surface topography of the powder samples exhibits nearly spherical shape microstructure and the average grain size has been found to be 180 nm (x = 0.05). The observed variations in the structural and magnetic properties are discussed in the light of existing understanding.

Structural, electrical and magnetic properties of (Fe, Co) co-doped SnO2 diluted magnetic semiconductor nanostructures

Nanostructures (NSs) of basic composition Sn1−xFex/2Cox/2O2 with x=0.00, 0.04, 0.06, 0.08 and 0.1 were synthesized by citrate-gel route and characterized to understand their structural, electrical and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase rutile type tetragonal structure. The crystallite sizes calculated by using Williamson Hall were found to decrease with increasing doping level. In addition to the fundamental Raman peaks of rutile SnO2, the other three weak Raman peaks at about 505, 537 and 688cm−1 were also observed. Field emission scanning electron microscopy studies showed the emergence of structural transformation. Electric properties such as dc electrical resistivity as a function of temperature and ac conductivity as a function of frequency were also studied. The variation of dielectric properties with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general. Hysteresis loops were clearly observed in M–H curves of Fe and Co co-doped SnO2 NSs. However, pure SnO2 nanoparticles (NPs) showed paramagnetic behaviour which vanished at higher values of magnetic field. The grain and grain boundary contribution in the conduction process is estimated through complex impedance plot fitted with non-linear least square (NLLS) approach which shows that the role of grain boundaries increases rapidly as compared to the grain volume with the increase of Fe and Co ions in to system.

Magnetocapacitance and impedance spectroscopy of Ba0.7Sr0.3TiO3/La0.67Sr0.33MnO3 and Ba0.8Sr0.2TiO3/La0.67Sr0.33MnO3 thin film heterostructures

The paper discuses synthesis of Ba0.7Sr0.3TiO3/La0.67Sr0.33MnO3 and Ba0.8Sr0.2TiO3/La0.67Sr0.33MnO3 thin film heterostructures by sol–gel (citrate gel route) method. The XRD spectra are determined for confirmation of crystalline phases of Ba0.7Sr0.3TiO3, Ba0.8Sr0.2TiO3 and La0.67Sr0.33MnO3 thin films. The observed variation of Cp, tan δ, magnetocapacitance (Mc), real part of dielectric constant e′, imaginary part of dielectric constant e″as a function of frequency, magnetoresistance R(H) and magnetoimpedance Z(H) are presented in the paper. Further the observed impedance spectra as a function of frequency f is also presented in the paper. The observed variation of Mc is qualitatively correlated with the stress induced effect and magnetoresistasnce effect occurring simultaneously.

Structural, electrical, and magnetic characterization of oxygen-deficient manganite La0.5Sr1.5Mn0.5Cr0.5O4-δ obtained by citrate precursor method

The oxygen-deficient manganite La0.5Sr1.5 Mn0.5Cr0.5O4-d has been prepared by citrate gel route at 1,300 C. Rietveld profile analysis shows that the phase crystallizes with tetragonal unit cell in the space group I4/mmm with oxygen deficiency at the O(1) site. The magnetic studies suggest that the ferromagnetic interac- tions are dominant because of Mn 3? -O-Mn 4? and Mn 3? - O-Cr 3? double exchange interactions. On analyzing the electrical resistivity data, it has been concluded that Mott's variable range hopping model fits well.

Study of specific absorption rate of strontium doped lanthanum manganite nanoparticles for self-controlled hyperthermia applications

Magnetic and magnetothermal properties of strontium doped lanthanum manganite La1−xSrxMnO3 nanoparticles have been studied with the strontium concentration x varying between 0.15 and 0.45. La1−xSrxMnO3 nanoparticles were prepared by the citrate gel route. XRD results show that all samples exhibit the characteristic perovskite structure with average particle sizes between 33 and 44nm. Adiabatic magnetothermia measurements were carried out in an RF magnetic field of 800A/m and 214kHz. Both magnetic and thermomagnetic behaviors are governed by the strontium content of the samples. The saturation magnetization, Curie temperature and specific absorption rate (SAR) vary non-monotonically with x. The SAR of the nanoparticles has been calculated using the linear response theory and good agreement with the experimental data has been observed. The intrinsic loss power (ILP) has been obtained from the SAR values. ILP values of our samples are comparable to those of magnetite.

Dielectric behavior of CaCu3Ti4O12 electro-ceramic doped with La, Mn and Ni synthesized by modified citrate-gel route

The effect of La3+, Mn2+ and Ni2+ doped calcium copper titanate, CaCu3Ti4O12 (CCTO), at higher concentrations (CR1 and CR2 with 5 mol% and 10 mol%, respectively), has been examined by semi-wet route at relatively lower temperature. This semi-wet route employs citrate-nitrate gel chemical method using TiO2 solid powders. X-ray diffraction (XRD) analysis confirms the formation of single phase in the doped samples sintered at 900 °C for 8 h. Scanning electron micrographs (SEM) show that the average grain size for CR2 is larger than that of CR1 composition. The energy dispersive X-ray spectroscopy (EDX) is used to study the percentage compositions of different ions present in both ceramics. Dielectric constant (ɛr) and dielectric loss (tanδ) values of CR1 are comparatively higher than those of CR2 ceramic at all measured frequencies and temperatures. The nature of temperature-dependent relaxation behavior of the ceramics is also studied by impedance, modulus spectroscopic analysis and confirms Maxwell-Wagner relaxation.

Dielectric and ac impedance studies of nanostructured CaCu3Ti3.90Ce0.10O12 electro-ceramic synthesized by citrate-gel route

Effect of doping at Ti4+ site by Ce3+ has been examined in CaCu3Ti3.90Ce0.10O12 synthesized by citrate-gel route. DTA/TG analysis of dry powder gives pre-information about formation of final product around 850 °C. X ray diffraction analysis confirmed the formation of CaCu3Ti3.90Ce0.10O12 phase of the ceramic sintered at 950 °C for 12 h. Microstructure has been studied using scanning electron microscopy and confirmed the average grain size found in nano range 200–400 nm in system CaCu3Ti3.90Ce0.10O12.The nature of relaxation behavior of ceramic was also rationalized by using the impedance and modulus spectroscopy. The bulk conductivity indicates an Arrhenius-type thermally activated process. The ac conductivity spectrum obeyed the Jonscher power law. The complex impedance diagrams of the ceramic exhibited a significant contribution from the grains, grain boundaries and electrode. The activation energies calculated from the grain-boundary relaxation time constant was found to be 0.49 eV which confirmed the Maxwell–Wagner type of relaxation present in the ceramic.