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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: 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]

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]