Abstract
In this paper, we report on the formation of novel hexagonal NiTiO3 nanopowders synthesized by the impregnation or co-precipitation methods through the thermal decomposition reaction of the precursors. The decomposition course was followed using differential thermal analysis (DTA) and thermogravimetric analysis (TGA) techniques. The intermediate decomposition products as well as the formed titanate were characterized using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. XRD patterns of the precursors calcined at 1000 degrees C showed the formation of the single ilmenite-type rhombohedral structure only with the impregnated precursor, while with the precipitated NiTiO3 powders one it indicates the presence of some NiO and TiO2 impurities. Transmission electron microscopy (TEM) exhibited loosely agglomerated hexagonal particles with uniform morphology having a size around 61 nm. The Brunauer-Emmett-Teller (BET) surface area measurements showed a type III isotherm with calculated surface area of 152 m(2)/g. The plot of In sigma ac vs. temperature as a function of frequency indicates a semiconducting behavior with ferroelectric phase transition at 605 K. The calculated activation in the ferroelectric region is 0.93 eV suggests the predominance of hopping conduction mechanism. Kinetic analysis of TG data according to different integral methods showed that in the NiC2O4 center dot 2H(2)O-TiO2 precursor, the water molecules are coordinately bounded and the presence of TiO2 reduces the activation energy needed to the oxalate decomposition reaction. (c) 2013 Published by Elsevier Masson SAS On behalf of Academie des sciences.