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Single-phase, nanosized La0.7Ca0.3Mn1−xNixO3 (x = 0, 0.02, 0.07, 0.1) manganites were synthesized via the autocombustion route. Information on the local geometric structure and the charge state of the Mn ions in the nanosized samples was gleaned from extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) data analysis, respectively. The experimental absorption spectra were recorded at room temperature at the K-edge of the Mn-ions. Analysis of the normalized XANES spectra showed that the Mn formal valence remained practically unchanged upon Ni2+ doping. Nevertheless, the observed broadening of the ruling absorption edge suggested that the repulsive nearest-neighbor potential, stemming from the shortening of the distances of Mn to the nearest-neighbor oxygen atoms (Mn–O bonds) in the coordination shell, was slightly modified. The values of the Mn–O distances were obtained from the Fourier transformed EXAFS spectra. A slight but sizeable decrease in the value of the Mn–O bond distances was verified, which pointed to a slight variation in the Mn3+/Mn4+ ratio sparked by the Ni2+ doping. Here, a generation of more Mn4+ ions with smaller radius (0.53 Å) was expected. The obtained Mn–O distances were compared with those resulting from the Rietveld refinement of the X-ray powder diffraction data. The variation of the 〈Mn–O–Mn〉 bond angle with Ni2+ doping was also determined from the analysis of the X-ray diffraction patterns, which allowed visualizing the small distortion of the MnO6 octahedra on substitution of Mn with Ni2+. [ABSTRACT FROM AUTHOR]

In this study, α-Fe2O3 was synthesized by solution combustion method using 6-aminohexanoic acid (AH) as a fuel and with different oxidizer-to-fuel ratios (Φ) of 0.6, 0.8, 1.0, 1.2, and 1.4. The as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and UV–Vis spectroscopy. The results showed that the Φ ratio played a crucial role in determining the crystallinity and purity of the powders of α-Fe2O3. The α-Fe2O3 powder synthesized at an Φ ratio of 0.6 exhibited phase purity of hematite. This study demonstrates the importance of controlling the Φ ratio in the synthesis of α-Fe2O3 which could be used as an inorganic pigment in paints. [ABSTRACT FROM AUTHOR]

The effect of sodium chloride (NaCl) on the magnetism of nanopowders of the spinel ferrite (MgFe2O4) produced using a salt-assisted solution combustion synthesis was investigated. X-ray diffraction (XRD) analysis was conducted to evaluate crystalline structure and phase composition of the synthesized materials. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to evaluate the particle size and morphology. Magnetic behavior was analyzed by measuring and analyzing the respective hysteresis loops using a vibrating sample magnetometer (VSM). The characterization showed that the presence of NaCl affects the phase composition, size, and dispersion of the nanoparticles, as well as their magnetic behavior. The theoretical size of the nanoparticles was calculated using the Scherrer equation, obtaining sizes of about 21.07 nm for the nanoparticles without salt, 5.90 nm for the sample salt content of 1.7 mol and 6.48 nm—for 3.4 mol. The synthesized nanoparticles showed a drastic decrease in coercivity field, remanence, and saturation with increasing salt content. Therefore, the salt content is a crucial parameter in controlling the morphology and magnetic properties of the nanoparticles obtained by the solution combustion route. [ABSTRACT FROM AUTHOR]

Manganese ferrite MnFe2O4 was synthesized by gel combustion synthesis using tris(hydroxymethyl)aminomethane (TRIS) as a fuel upon variation of oxidizer-to-fuel ratio Ψ and characterized by XRD, Raman spectra, and vibrating sample magnetometry (VSM). The measured values of saturation magnetization Ms = 27.70 emu g–1 and coercivity Hc = 86.87 Oe are indicative of superparamagnetiс behavior of synthesized materials. Our results also show that TRIS could be readily used as an alternative fuel to synthesize spinel ferrites through a one-step process of solution combustion synthesis. [ABSTRACT FROM AUTHOR]