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The paper had as purpose the fabrication and characterization of magnetic nanoparticles covered with TiO2 for applications in environmental field. The research consisted in investigating the properties of magnetic iron nanooxides, synthesized from ferric and ferrous chloride and then covered with TiO2, with minimum costs and high efficiency in industrial wastewater treatment. The iron nanoparticles were obtained by co-precipitation method and the titan dioxide was obtained by sol-gel method. After covering the nanoparticles with TiO2, the samples were characterized by X-Ray diffraction (XRD) and scanning electron microscopy (SEM).

Graded structures with different architectures were obtained by spark plasma sintering from (Ba1-xSrx)TiO3(BST, x = 0.10; 0.20; 0.30) powders. The presence of the composition gradient was confirmed by structural and compositional investigations using X-ray diffraction and electron microscopy combined with energy dispersive X-ray spectroscopy. The concentration gradient was either asymmetric (3 layers, starting with x = 0.10 and ending with x = 0.30) or symmetric (5 or 6 layers, starting and ending with x = 0.10, and with a single or double x = 0.30 layer in the middle, respectively). Electrical measurements reveal a decrease of the dielectric constant with increasing the number of the layers. It was found that the symmetric graded structure with 6 layers has the best thermal stability of both, the dielectric constant (variation of only 8% between zero and 100 °C) and the pyroelectric coefficient (6% variation between zero and 80 °C). In addition, an enhancement of the pyroelectric signal for frequencies above 100 Hz is obtained in symmetric structures, an effect that is attributed to the additive contributions of the signals originated from the layers with different Sr content.