Citrate Gel Route Research Articles

Coexistence of Superconductivity and Ferromagnetic Phases in YBa2Cu3O7−δ Nanoparticles

High-temperature superconductor YBa2Cu3O7−δ (YBCO) nanopowders were synthesized by the citrate-gel route, which is a modification of the sol-gel method. The fine powders were calcinated at 860 and 900 °C. They were of small size, in the range of 30–35 nm. X-ray diffraction (XRD) patterns verified production of the orthorhombic superconducting phase in all samples. Measuring the magnetic properties of these nanoparticles at room temperature, via a vibrating sample magnetometer (VSM), indicated ferromagnetism behavior in the YBa2Cu3O7−δ nanoparticles. As the size of the nanoparticles decreased, the magnetic saturation of all samples increased. The development of the ferromagnetism effect was attributed to the presence of surface oxygen vacancies that lead to electron redistribution on the different ions at the surface. Thus, in an innovative work, the produced samples were annealed at 700 °C for 5 h under 0.8–0.9 bar of air atmosphere. The results showed that a small increase in the nanoparticle size provided a dramatic increase of magnetic saturation in all samples. Thus, we can say that the annealing process at vacuum improves the ferromagnetic properties of YBCO nanoparticles.

Magnetic and electrical properties of In doped cobalt ferrite nanoparticles

Nanoparticles of CoFe2O4 and CoIn0.15Fe1.85O4 ferrites were prepared 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 cubic spinel structure. The average grain sizes from the Scherrer formula were below 50 nm. Microstructural features were obtained by scanning electron microscope and compositional analysis by energy dispersive spectroscopy. The hysteresis curve shows enhancement in coercivity while reduction in saturation magnetization with the substitution of In3+ ions. Enhancement of coercivity is attributed to the transition from multidomain to single domain nature. Electrical properties, such as dc resistivity as a function of temperature and ac conductivity as a function of frequency and temperature were studied for both the samples. The activation energy derived from the Arrhenius equation was found to increase in the doped sample. The dielectric constant (ε′) and dielectric loss (tan δ) are also studied as a function of frequency and temperature. The variation of dielectric properties ε′, tan δ, and ac conductivity (σac) with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general and the hopping of charge between Fe2+ and Fe3+ as well as between Co2+ and Co3+ ions at B-sites. Magnetization and electrical property study showed its dominant dependence on the grain size.

Effect of A-site substitution on electrical conductivity and microstructure of YAlO3

Abstract

Improved crystallinity, spatial arrangement and monodispersity of submicron La0.7Ba0.3MnO3 powders: A citrate chelation approach

The perovskite manganite systems have been the materials of tremendous interest due to their strong correlation between structure, transport and magnetism. These materials in their single-crystal form show colossal magneto-resistance (CMR), but the applied fields are very high (∼1–5T). The polycrystalline samples do show high low-field magneto-resistance (LFMR), but good amount of control over particle sizes and grain-boundary distribution is required, which is well known but less realized in practical approaches. In this context, we report on synthesis and manipulation of polycrystalline La0.7Ba0.3MnO3 (LBMO) submicron powders using citric acid chelation. The Citrate-gel route is used to synthesize poly-dispersed LBMO powders which are subjected to citrate chelation for a duration of 0 (LB0) to 4h(LB4) . The samples show improved ordering in X-ray diffraction patterns. Raman spectroscopy scans indicate changed mode signatures due to the probable chelating process, which alters the surface morphology. X-ray photoelectron microscopy shows an evidence of fine citrate layer on the grain boundaries. Low temperature B–H curves exhibit fine hysteresis loops for all samples, while room temperature B–H curves shows paramagnetic response. Scanning electron microscopy images showed the formation of well arranged, connected, mono-dispersed grains of LB4 sample, as against polydispered LB0. The magneto-resistance (at H=100kOe) is seen to enhance for LB4 at its transition temperature (75%, as compared to LB0, where it is 60%), which can be attributed to the well-controlled inter-grain tunneling phenomenon and thin insulating regions in between, created due to citrate chelation, which probably enhances the scattering phenomenon and its susceptibility to applied fields. As citric acid is known to chelate Mn ions, it probably chelates the smaller LB particulate structure and leaves behind citrate-connected submicron grains of LBMO, which are seen to be well engineered.

Correlation Between Charge, Spin and Lattice in La–Eu–Sr Manganites

To understand the structural, electrical, magnetic, elastic and anelastic properties of La0.67−xEuxSr0.33MnO3 (0.30≤x≤0.39) manganites, a series of samples was prepared by citrate gel route. X-ray diffraction studies along with Rietveld analysis indicate the samples crystallize in single phase with Pnma space group. Studies on the variations of magnetization with temperature indicate that the Curie transition temperature (TC) decreases with increasing Eu content. Furthermore, Eu substitution is found to increase the electrical resistivity and significantly enhances the colossal magnetoresistance effect, while it is found to decrease the characteristic metal–insulator transition temperature (TP). On analyzing the electrical resistivity data, it has been concluded that the resistivity below TP can be explained based on electron–electron, electron–phonon and two magnon scattering processes, while that above TP, the adiabatic small polaron model is found to explain the observed behavior. Finally, the longitudinal modulus (L) and internal friction (Q−1) have been measured and a dramatic change in L (T) is observed at TC, accompanied by a sharp peak in Q−1 (T). Simultaneous occurrence of magnetic, transport and lattice anomalous behavior at TC indicate the presence of strong electron–phonon and spin–phonon interactions in these manganites.

Improvement of Morphology and Luminescence Properties of Powellite Type Red Phosphors CaGd1−xNbMoO8: xEu3+ Synthesized via Citrate Gel Route

Powellite type molybdate‐based red phosphors CaGd1−xNbMoO8: xEu3+ (x = 0.05, 0.1, 0.15, 0.20, 0.25, and 0.30) were synthesized by a solid‐state reaction (SSR) route, and a citrate gel (CG) route. The crystalline structure, morphology, absorbance, and luminescent properties of these phosphors were characterized using powder X‐ray diffraction, scanning electron microscopy, UV visible absorption spectroscopy, and photoluminescence spectroscopy. The solid solution formation of the phosphor effectively takes place at a lower temperature by the CG route than the SSR route. Particle morphology of the phosphors prepared by the CG route reveals that they are less agglomerated, more spherical, and homogenous in nature with uniform particle size. Investigations on photoluminescence properties show that these phosphors emit strong red light (614 nm) under both near UV (395 nm), and blue (465 nm) excitations. The morphological variation of the developed phosphors with respect to synthesis method and heat treatment played an important role in their luminescence enhancement. The red phosphors prepared via CG route were characterized by enhanced and sharper red emission with longer life time compared to that of phosphors synthesized via SSR route. The CIE color coordinates of the developed red phosphors are (0.65, 0.34) that are closer to NTSC standard red phosphor. Thus, these phosphors could be a promising red candidate for the phosphor converted white light emitting diode applications.

Catalytic soot combustion of α-Fe/Ce–K–O nanocomposites via citrate-gel route

The binary phase, porous, nanocomposite xα-Fe/(1 − x)Ce0.9–K0.1–O (x = 0.05–0.2) catalysts and the catalyst-coated honeycomb ceramic device have been prepared by the citrate-gel thermal decomposition-reduction process and the sol–gel assisted dip-coating method, respectively. The nanocomposite of fluorite-type structure CeO2 nanoparticles about 18–51 nm and α-Fe nanoparticles about 32 nm is obtained at 600 °C for 2 h in a deoxidization atmosphere and the α-Fe in nanocomposite has the suppression effect on grain growth of CeO2. With Fe content increasing from 0.05 to 0.1, the specific surface area for the nanocomposites increases dramatically from about 4.4 to 43.0 m2/g, reaching a maximum value 57.7 m2/g at x = 0.15, and the pores vary from macropores to micro- or mesopores. Due to the presence of nano α-Fe, all the catalysts exhibit a very high soot catalytic activity, with the lowest T20 (255 °C) and T50 (291 °C) for the nanocomposite with x = 0.15, and it is confirmed by the bench test under practical diesel exhaust gases.

Single-Step Microwave-Assisted Synthesis of La<SUB>0.6</SUB>Sr<SUB>0.4</SUB>Co<SUB>0.2</SUB>Fe<SUB>0.8</SUB>O<SUB>3–<I>δ</I></SUB> Perovskite

La0.6Sr0.4Co0.2Fe0.8O3-delta perovskite powder was prepared by a single-step process based on a microwave-assisted citrate gel route. The structure, morphology, as well as surface properties and th ...

Citrate gel route for synthesis of dense pyrochlores

The solid solution of pyrochlore oxides, Nd 2Zr x Ti 2− x O 7 ( x = 0.2, 0.4, 0.6, 0.8 and 1.0) was synthesized by citrate gel method and the conventional ceramic method. The results indicate that the citrate gel method gives pyrochlore phase formation at a much lower temperature and better morphology of the product oxides as compared with the ceramic method. The dc conductivity study was carried out on some samples to understand the defects, if any, in the lattice of the solid solution Nd 2Ti x Zr 2− x O 7 ( x = 0.2, 0.4, 0.6, 0.8 and 1.0) on substitution of Zr by Ti. The formation of defects in the lattice on substitution of Zr by Ti, was explained on the basis of XPS studies.

Elastic anomalies of La 0.67Sr 0.33− xBa xMnO 3 in the vicinity of TC

With a view to understand the elastic behaviour of a material system, La 0.67Sr 0.33− x Ba x MnO 3 (where x=0, 0.1, 0.2, and 0.33) especially in the vicinity of their magnetic transition temperature T C , a systematic investigation of ultrasonic velocity over a temperature range 300–400 K has been carried out. The materials prepared by citrate gel route, were characterized structurally by XRD and on analyzing the XRD patterns, it has been concluded that all the samples are having rhombohedral structure with space group of R3̄c. The magnetic ( T C ) transition temperatures determined by AC susceptibility measurements are found to decrease continuously with increasing barium concentration. Finally, the ultrasonic longitudinal velocities of all the samples are found to exhibit considerable softening in the vicinity of their magnetic transition temperatures, T C and the observed behaviour is explained using mean field theory and Jahn–Teller theorem.

SYNTHESIS AND MICROWAVE DIELECTRIC PROPERTIES OF Li2MgSiO4 CERAMICS PREPARED USING CITRATE GEL ROUTE

The comparison of the low temperature sintering and the microwave dielectric properties of Li2MgSiO4 (LMS) ceramics prepared by citrate gel (CG) route and solid state (SS) ceramic route are discussed in this paper. The LMS prepared using CG route sintered at 1175°C/2 h has εr = 5.3 and tan δ = 1 × 10−3 at 9 GHz. The sintering temperature of LMS is lowered to 950°C with the addition of 5 wt% lithium magnesium zinc borosilicate glass and has εr = 5.6 and tan δ = 2 × 10-3 at 9 GHz. The amount of glass required to lower the sintering temperature of ceramics prepared using CG are slightly higher than that of SS ceramic route. The LMS ceramics prepared using SS ceramic route shows excellent microwave dielectric properties with low sintering temperature compared to CG route.

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1−x Co x O3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd0·5Sr0·5Mn\(_{{\rm 1}-{x}}\)Co\(_{{x}}\)O3 (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn3 + –O2 − –Mn4 + as compared to Co3 + –O2 − –Co4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile \({e}_{\rm g}\) electrons).

Catalyst efficiency, photostability and reusability study of ZnO nanoparticles in visible light for dye degradation

Polydispersed ZnO nanoparticles (ZnO1000 and ZnO600) with two different windows of particle size distributions (∼120 and 30 nm) were synthesized using citrate gel route and different annealing treatments (1000 and 600 °C, respectively). Photocatalytic efficiency of these samples was compared with TiO 2 in its commercial form-P25, on two dyes, Methylene blue (MB) and Methyl orange (MO). The X-ray diffraction data showed wrutzite ZnO and anatase and rutile phases of P25. UV–visible absorbance spectra of ZnO1000 showed broad absorption range from UV-to-visible (from 382 to 700 nm), as against sharp absorption peaks in UV range for both ZnO600 and P25. The microstructural morphology as seen through scanning electron micrographs showed ZnO1000 with tetrapod-like structures while the ZnO600 showed almost spherical morphologies. Upon subjecting these catalysts to dye solutions in sunlight it was found that both the dyes were completely decolorised within 20 min by ZnO1000, as against partial decolorisation by ZnO600 and P25 ( 53% and 78% for MO and 77% and 88% for MB samples). The effect of catalyst loading (from 125 mg to 1 g) on decolorisation showed that ZnO1000 had good efficiency for all concentrations which was followed by P25 and then by ZnO600. Small perturbations are attributed to the competition between sunlight scattering-induced, reduced irradiation field and the exposed surface area offered by catalyst, which work as active sites for decolorisation. The reusability of the catalysts when studied on fresh dye samples (4 trials), the decolorisation efficiency decreased merely from 99.2% to 99.12% for ZnO1000 as compared to ZnO600 (53.3% to 19.94%) and P25 (78.3% to 31.42%), indicating the efficient reusability of ZnO1000. The effective half life of the catalysts, in terms of number of reuses, were calculated and found to be ∼3 for both ZnO600 and P25 and was >3000 for ZnO1000, which justifies its extremely high reuse. The byproduct analysis (compared with standards prescribed by World Health Organisation (WHO) and Central Pollution Control Board of India (CPCB)) showed cleavage of the chromophore and of other bonds with opening of benzene rings, indicating degradation of the dyes in concurrence with decolorisation, in the stipulated time. Further, cytotoxicity studies performed on SiHa cell lines showed non-toxicity of the byproducts with ZnO1000 as compared to ZnO600 and P25.

Synthesis of gadolinium aluminate powder through citrate gel route

Nanocrystalline gadolinium aluminate (GdAlO 3) powder was prepared through citrate gel route. The thermal decomposition behavior of gadolinium–aluminium–citrate–nitrate precursor powder was studied with the help of thermo gravimetric analysis combined with differential scanning calorimetry and mass spectroscopy. The phase evolution of the powder at different temperatures was characterized by high-temperature X-ray diffraction. The decomposition of the precursor powder in oxidizing atmosphere was found to be a three-step process: (i) evolution of water and ammonia; (ii) evolution of carbon dioxide, residual water, and ammonia; (iii) oxidation of residual carbon. Calcination of precursor powder at 800 °C under static air was found to result in GdAlO 3 phase. In the absence of oxidizing atmosphere the amorphous precursor powder only partially crystallized into GdAlO 3 phase at 1200 °C.

Chemical synthesis and characterization of Ca-substituted YAlO 3 as electrolyte for solid oxide fuel cells

In this study, perovskite type oxide YAlO 3 has been doped with different amounts of the divalent cation Ca to synthesize Y 1− x Ca x AlO 3− δ ( x = 0–0.21) compositions. The effect of dopant concentration on the crystal structure and electrical properties of YAlO 3 synthesized by citrate gel route has been investigated. The phase purity of the samples has been carried out using X-ray diffraction. The microstructural evaluation of the samples has been conducted by scanning electron microscopy and energy dispersive spectrum analysis. Thermal analysis has been conducted to monitor the decomposition of the intermediate products. The electrical conductivity studies have been performed using a.c. impedance spectroscopy as a function of temperature in the range 200–800 °C in air. The Y 0.94Ca 0.06AlO 3− δ composition exhibits a total conductivity of 2.5 mS/cm at 800 °C.

Study on phase evolution of GdAl1−Ga O3 system

Abstract In the present investigation, phase evolution of GdAl1−xGaxO3 system was investigated by preparing a series of powders through citrate gel route. The powders were calcined at 1000 °C for 2 h and characterized for phase purity using X-ray diffraction (XRD). Sintering of a few selected compositions was carried out at 1550 °C for 4 h. The microstructural analysis of the sintered specimens was carried out using scanning electron microscopy (SEM) coupled with energy dispersive X-ray analyzer (EDS). It was observed that the preparation of GdGaO3 through citrate gel route resulted in the formation of two-phase mixture of Gd3Ga5O12 and Gd2O3. In GdAl1−xGaxO3 system, gallium could be dissolved in GdAlO3 lattice up to a doping level of 4 mol%. At higher doping level, the un-dissolved gallium precipitated in the form of Gd3Al4GaO12.

Synthesis and structure–property relations in xCuO–(1−x)Bi2O3 (0.5⩽x⩽0.9) (C1–C5: x=0.5, 0.6, 0.7, 0.8, 0.9) glasses

Synthesis of the x CuO–(1 − x )Bi 2 O 3 (0.5 ⩽ x ⩽ 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses was done via nitrate–citrate gel route. Glassy phase is ascertained by XRD studies. Magnetic susceptibility results in the range 4.2–400 K show weak paramagnetic nature with exchange integrals ∼0.024–0.13 eV in the glasses. The electron paramagnetic resonance (EPR) in the range 4.2–363 K shows g ≈ 2.0 and the trend of the g -matrix elements g || > g ⊥ > g e for the glasses C1–C5 at 4.2 K are due to the Cu 2+ (3d 9 ) paramagnetic site in the glasses which is in a tetragonally elongated octahedron [O 1/2 –CuO 4/2 –O 1/2 ] having D 4h symmetry. IR spectroscopic results show the presence of octahedron [BiO 6/2 ] 3− and [CuO 6/2 ] 4− units and pyramidal [BiO 2/2 O] − unit in the glasses.

Elastic behaviour of strontium-doped lanthanum calcium manganites in the vicinity of TC

Colossal magnetoresistance (CMR) manganites with compositional formula, La 0.67Ca 0.33− x Sr x MnO 3 (where x=0, 0.09, 0.11, 0.13, 0.33) were prepared by citrate gel route mainly to understand the elastic behaviour in the vicinity of their magnetic transition temperature T C. The structural characterizations of all the materials clearly indicate that samples upto x=0.13 doping, are having orthorhombic structure with Pbnm space group and sample with x=0.33 is having rhombohedral structure with R 3 ¯ c space group. The magnetic transition temperatures ( T C) are determined by AC susceptibility measurements and are found to increase continuously with increasing strontium concentration. Finally, a systematic investigation of the ultrasonic longitudinal velocities of all the samples was carried out. Further, all the samples are found to exhibit anomalous behaviour in the vicinity of their magnetic transition temperatures and the observed behaviour is explained using Landau's theory.

Synthesis and characterization of microwave processed PZT material

With a view to investigate the influence of microwave sintering on the structural and dielectric properties of lead zirconate titanate (PZT), the samples were prepared by citrate gel route. The well crystallized single phase perovskite PZT powders were obtained after calcination at 700 °C for 2 h. The X-ray diffraction (XRD) pattern clearly indicates the formation of PZT material with single phase. FTIR and TG-DTA studies also confirmed the formation of PZT along with the reaction process involved in the synthesis. The crystallite sizes of the samples calcined at different temperatures were calculated using Scherrer’s formula and were compared with those obtained by the transmission electron microscope (TEM) technique. The surface morphological features of all the samples were studied using a scanning electron microscope (SEM) while the chemical composition was obtained by an energy dispersive X-ray spectroscope (EDS). The variation of dielectric constant and loss tangent with temperature and frequency of both the type of samples was also investigated and the observed behavior is explained qualitatively.

Investigations on Ru doped ZnO: Strain calculations and gas sensing study

Pure and ruthenium (Ru) doped nano-crystalline zinc oxide (ZnO) powders were synthesized by using well-known citrate gel route. Citric acid acts as a chelating agent and thus helps in the formation of nanoparticles. The detailed X-ray diffraction (XRD) studies using Hall equation reveal that in the nanoscale dimensions, incorporation of Ru modulates the lattice strain. It is interesting to note that on Ru doping, the compressive strain present in the undoped ZnO changes into tensile strain. We have tested the response of these specimens individually for reducing gases like H 2, LPG (liquefied petroleum gas), C 2H 5OH (ethanol), CO, acetone and oxidizing gases like NO x and Cl 2. Undoped ZnO responses perceptibly to LPG while Ru doped sample highly senses ethanol vapors. This might be due to either change in composition on Ru doping or/and difference between basicity of LPG and C 2H 5OH vapors.