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In this paper, ferrogels comprising nanocrystalline Fe3O4 and γ-FeOOH dispersed in polyvinyl alcohol gel matrix were synthesized via a novel route, without using any cross-linking agent. A moderately high-pressure environment instead was used for the synthesis. The ferrogels were found to be stable over a long period of time and were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy and DC magnetization studies. TEM studies showed that the particles are mostly spherical with an average size of 10 nm. Mössbauer spectra of the as prepared gels at different temperatures showed the presence of superparamagnetic particles in them. The gels were found to be magnetically ordered at 20 K giving characteristic six-finger Mössbauer patterns. Bulk magnetic properties of the gels were studied by DC magnetization measurements. [ABSTRACT FROM AUTHOR]

In this paper, nickel nitrate, copper nitrate, cobalt nitrate, ferric nitrate were used as raw materials, citric acid was used as a complexing agent, and chromium nitrate was used as a modifier to synthesize Ni 0. 2 Cu 0. 2 Co 0. 6 Cr x Fe 2 − x O 4 by sol–gel method. The sample was characterized. X-ray diffraction (XRD) data on the sample showed that the particle size of the sample was 52.14–54.88 nm. The lattice constant varied from 8.3569 Å to 8.3758 Å. The data of Fourier infrared showed that the sample did not change with the structure of the doped sample of Cr ion and remained as the spinel type. It can be seen by SEM that the sample is irregularly spherical. Due to the doping of chromium ions, it appears agglomerated. Analysis of the elements of the sample by EDAX revealed that the sample contained Ni, Cu, Co, Fe, O and a peak corresponding to the Cr element was found in the sample having crion content of 0.025, 0.050, 0.075 and 0.100. The magnetic properties of the samples were characterized using VSM. The data are processed to obtain magnetic parameters such as saturation magnetization and coercivity. [ABSTRACT FROM AUTHOR]

In this paper, a series of rare-earth-doped barium hexaferrite powders (Ba0.95Re0.05-Fe12O19 and Ba0.95Re0.05M0.05Fe11.95O19: Re = La, Pr, Sm, Nd, Gd, Dy, Yb; M = Zn2+, Mn2+, Mn2+0.5 Zn2+0.5) were synthesized by the sol–gel self-combustion technology. The phase composition and the magnetic properties of the as-prepared barium hexaferrites were characterized and discussed with X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that the barium hexaferrites exhibited the magnetoplumbite phase structure with the average diameter of 45 nm. Magnetic properties study revealed that the variation of the saturation magnetization (Ms) was similar with the change of the rare-earth ions radius, but the change of Ms was low. This indicated that the magnetic moments of rare-earth ions could not affect Ms. The magnetocrystalline anisotropy field mainly influenced the anisotropism of hexaferrites, and the coercivity (Hc) of the rare-earth ions doped barium hexaferrites basically decreased with the increasing orbital quantum numbers (except Sm3+ and Gd3+). Further study showed the co-addition of Zn2+ and Mn2+ did not change the trend of Ms and Hc. Thus, it is concluded that the rare-earth ions played an important role for the anisotropy field of barium hexaferrites. [ABSTRACT FROM AUTHOR]

Li-Co nanoferrites (LiCoFeO4) with x = 0.00, 0.03, 0.06, 0.09, and 0.12, were synthesized by chemical sol-gel method. Two different sintering techniques viz. conventional technique (CT) and microwave technique (MT) were employed to heat treat the synthesized samples with an aim to study the effect of sintering technique on the properties of the nanoferrites. Structural and microstructural properties of the samples were investigated using XRD and scanning electron microscopy (SEM) technique, respectively. The variation of room temperature dielectric constant and dielectric loss were measured as a function of frequency in the range 100 Hz-1 MHz and the normal dispersive behavior was observed. Magnetic properties were investigated using Vibrating Sample Magnetometer (VSM), while Soohoo's method was used to measure Curie temperature. The results obtained have been discussed in the paper. [ABSTRACT FROM AUTHOR]

In this paper, potassium sodium niobate (KNN) nanopowders were successfully obtained by sol-gel combustion method. According to thermogravimetric analysis (TGA) results, the produced xerogel was calcined at 500C, 600C, and 700C to obtain KNN powders. The structural and optical properties of the prepared powders were studied using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and UV-vis spectroscopy. The XRD patterns indicated formation of orthorhombic KNN samples. The Scherrer formula and size-strain plot (SSP) method were employed to calculate crystallite size and lattice strain of the KNN powders. The TEM image revealed that the average particle size of the prepared samples is about 30 nm and they have cubic shape. The optical band gap energy of the samples was calculated using UV-vis absorbance spectra of the samples along with Tauc relation. [ABSTRACT FROM AUTHOR]

Hexagonal yttrium manganites, YMnO3, are interesting materials for their multiferroic behavior. Substituting suitable cations either at the Y-site or Mn-site offers great opportunities to produce a variety of manganites and tune their properties. Nanocrystalline yttrium iron manganites with the compositional formula YFeMnO3, = 0.0, 0.10, 0.15, 0.20 and 0.25, were synthesized by sol-gel autocombustion method. The prepared samples were heated at 1100C for 1 h. Another set of samples with compositional formula YFeMnO3, = 0.0, 0.10, 0.15, 0.20 and 0.25, were also synthesized by the same method and heated at 1100C for 1 h. Various characterizations were done on these manganite systems synthesized by substituting iron at different sites. X-ray diffraction (XRD) technique studied the structure of the samples and analysis of XRD patterns confirmed the formation of hexagonal phase in the samples. Structural parameters such as lattice constants, crystallite size, theoretical density, etc. were determined using the XRD data. The unit cell dimensions have been found to agree with the standard data and the Debye-Scherrer crystallite size obtained from XRD data ranges from 42 nm to 77 nm. The room temperature frequency variations of electrical properties such as dielectric constant, dielectric loss and AC conductivity were measured in the range of 100 Hz-2 MHz and the variations showed a dispersive behavior for all the samples. The various measurements and the results obtained were studied and discussed in the paper. [ABSTRACT FROM AUTHOR]

(K0.5Na0.5)NbO3 lead-free nanopowders were synthesized by a modified sol-gel method in different media: gelatin, starch and chitosan, as polymerization and stabilizer agents. The proper temperature needed for calcinating the prepared gel was obtained using thermogravometric analysis (TGA). Structural and optical properties of the prepared powders were investigated and compared using X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-Vis diffused reflectance spectroscopy. The XRD patterns of the synthesized samples confirmed the formation of the orthorhombic structure at 600°C calcination temperature with no remarkable extra peaks. TEM images showed that the morphologies of the particles prepared in the three different media are cubic with the average size of about 69, 34 and 49 nm for gelatin, starch and chitosan, respectively. The value of the energy band gap of the samples was calculated by diffused reflectance spectroscopy, using Kubelka-Munk method. Our results showed that the type of the polymerization agent is important in preparing KNN nanoparticles and affects the structural and optical properties of the synthesized samples. [ABSTRACT FROM AUTHOR]

Coatings composed of mixed nanoparticles in Silica and Titania sol matrices were prepared by sol-gel spray coating method. The coatings were characterized using scanning electron microscopy (SEM), FT-IR spectroscopy and Infrared thermal imaging. The thermal Infrared Emissivity of the coatings was determined using IR-1 spectrometer. The coating solutions were applied onto sand blasted aluminum substrates. Results indicated that mixed nanoparticles can be well dispersed in sol to give coatings with good heat emission properties. High emissivity of 0.915-0.941 was achieved, and the coatings showed cooling efficiency of 7.3-14%. The coatings can be prepared in an easy and controlled way using sol-gel method and are a potential in radiative cooling applications. [ABSTRACT FROM AUTHOR]

Pb containing ruthenium-based superconducting cuprates Ru(Sr1.5Ca0.5)PbCu2O8 (Ru-1212 type) have been successfully synthesized through the sol–gel route. The optimum annealing temperature for the ruthenium-based cuprate superconductor was found to be 890°C. The crystal structure determined by X-ray powder diffraction method showed a single Ru-1212 type phase with tetragonal symmetry with lattice parameters a = b = 3.920 Å, and c = 11.76 Å. The Ru(Sr1.5Ca0.5)PbCu2O8 material showed onset temperature, Tc-onset at 35 K and zero resistant temperature, Tc-zero at 20 K. Pb together with the partial substitution of Sr with Ca lowered the formation temperature of the Ru-1212 type phase. [ABSTRACT FROM AUTHOR]