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Cobalt ferrite nanopowders were synthesized by means of the sol-gel method, using citric acid as a chelating agent, and various alcohols as gelling agent: ethanol (ET), ethylene glycol (EG), polyvinyl alcohol (PVA), 1,3 propanediol (PD) and a mixture of PVA and EG. The simultaneous TG/DTA analysis revealed different thermal behaviours of the synthesized gels, depending on the gelling agent. The powders obtained at 500 °C and annealed at 700 °C and 1000 °C contain a single CoFe 2 O 4 phase. Scanning electron microscopy (SEM) revealed the influence of the gelling agent on the morphology of cobalt ferrite particles. The coercivity and the saturation magnetization of the powders obtained at 500 °C showed a strong dependence on the crystallite size, determined by the nature of the gelling agent. [ABSTRACT FROM AUTHOR]

Sodium niobate (NaNbO3) fine powders were synthesized by hydrothermal method using ammonium niobate (V) oxalate hydrate (C4H4NNbO9 x H2O), sodium hydroxide (NaOH) and sodium citrate hydrate (C6H9Na3O9) as precursors. The samples were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), AFM (Atomic Force Microscopy), UV-VIS spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). X-ray diffraction for powder obtained by hydrothermal method revealed three phases mixture (NaNbO3, Nb2O5, Na2C2O4). In order to obtain a material with perovskite structure, the powder was treated for 6 h at 600°C. After calcination, the X-ray powder diffraction (XRD) patterns shown reflections of a pure cubic structure (space group Pm-3m) with lattice parameters (a=b=c=3.909Å) comparable to those reported in the literature. The average particle sizes estimated by SEM image were 2-3 micrometers. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a study regarding the cobalt ferrite obtaining in the Co x Fe3−x O4 system, where x =0.5; 1.0; 1.5 by two different synthesis methods. The Co(II) and Fe(III) complexes method leads to the thermal decomposition at 300°C for this precursor with the pure cobalt ferrite (CoFe2O4) formation for x =1 or mixed with γ-Fe2O3 for x =0.5 and Co3O4 for x =1.5. By co-precipitation followed by ultrasonic milling synthesis method the pure cobalt ferrite is obtained at 90°C for x =1 or mixed with Fe3O4 for x =0.5 and Co3O4 for x =1.5. When the initial samples are heated at 400°C, the identified oxide phase is identical for the same value of x. The obtained powders were investigated by X-ray diffraction (XRD), FTIR spectrometry and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDX). The final product has nanometric size and has a strong tendency to agglomerated, thus influencing the saturation magnetization value. The shape of the magnetization curves is influenced by the presence of the secondary phases for x ≠1. [Copyright &y& Elsevier]

Two samples of NaTaO3 perovskite materials were prepared by the standard hydrothermal method at the same reaction temperature (600 °C) but with different sintering times: 6 hours for sample S1 and 12 hours for sample S2. Using X-ray diffraction (XRD), it shows that samples S1 and S2 are mixtures of Na-Ta oxides (Ta2O5 and the prevailing phase NaTaO3). The scanning electron microscopy analysis (SEM), shows that the grains are connected each other in agglomerated clusters of size about few hundred nanometers. The frequency (f) dependencies of complex impedance, Z(f) = Z'(f) – i Z''(f) of the samples, over the frequency range 20 Hz – 2 MHz, at room temperature are presented. The real component Z' of the complex impedance decreases with increasing frequency and the imaginary component Z'' has two maximum corresponding to two relaxation processes. The results obtained from the complex impedance spectroscopy, Z''(Z') showed the appearance of two semicircles, corresponding to grain and grain boundary mechanism. Experimental results have been fitted with two parallel RC equivalent circuits connected in series and the parameters R and C have been evaluated. [ABSTRACT FROM AUTHOR]