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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]

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]

Abstract: ZnGa2O4 phosphor doped with Eu3+ ions was synthesized by hydrothermal method using two concentrations: 3.34mol% and 1.67mol% of Eu3+. The crystal structure was investigated by means of X-ray diffraction, scanning electron microscopy and atomic force microscopy. The results indicate that the material consisting of ZnGa2O4:Eu3+ nanoparticles exhibits good crystalinity, with cubic spinel structure. The powders were found to have 4.74eV of ZnGa2O4:Eu3+ (3.34mol%) and 4.69eV of ZnGa2O4:Eu3+ (1.67mol%) band gaps, respectively. The luminescent analysis of the materials shows that the trivalent europium ions doped in this material are localized in different sites, substituting both Zn2+ and Ga3+. The emission spectra of the europium-doped samples, originating from 5D0–7F J (J =0–4) transitions, suggests the existence of three different site symmetry of Eu3+ ions, tetrahedral (Zn2+), distorted octahedral (Ga3+) and low octahedral (Ga3+) sites, respectively. [Copyright &y& Elsevier]

The study herein reports the synthesis by hydrothermal method at 200 °C for 12 h, followed by heat treatment at 600 °C for 6 h of NaNbO 3 materials, undoped and Zr-doped at different concentrations (1, 2 and 3%). The influence of Zr doping in NaNbO 3 compounds on the morpho-structural and optical properties as well as their dependence on dopant concentration was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM-HRTEM/EDX), Fourier transform-infrared (FT-IR), Raman and Ultraviolet-Visible (UV-Vis) spectroscopy. An orthorhombic structure (P mc 2 1 space group) is characteristic for undoped NaNbO 3 and 1% Zr-doped NaNbO 3 materials, while 2 and 3% Zr-doped NaNbO 3 present the tetragonal symmetry (P4/mbm space group). Results show different morphologies depending on the dopant concentration (cubic shape particles for undoped and 1% Zr sample while for 2 and 3% Zr wire-like morphology is observed) and a slight increase of the optical band gap with increasing Zr concentration from 3.61 eV (undoped NaNbO 3) to 3.73 eV (3% Zr: NaNbO 3). [ABSTRACT FROM AUTHOR]