Nanostructured Oxides Based on Niobate with Tetragonal Tungsten Bronze Structure Synthesized by Spray Pyrolysis Method.

Reference	Presenter	Authors (Institution)	Abstract
13-017	SILVANIA Lanfredi	Lanfredi, S.(Faculdade de Ciências e Tecnologia); Praxedes, F.R.(Faculdade de Ciências e Tecnologia); Djurado, E.(Université de Savoie, Université Joseph Fourier); Nobre, M.A.(Faculdade de Ciências e Tecnologia);	Niobates with tetragonal tungsten bronze TTB-type structure have been considered as promising ferroelectric materials, besides to having catalytic and photocatalytic properties. However, these properties depend on the morphology of the powder and synthesis method. This work investigated the preparation of nanometric particles of KSr2Nb5O15 and Ni-doped KSr2Nb5O15 with stoichiometry KSr2(Ni0.25Nb4.75)O15-delta and KSr2(Ni0.5Nb4.5)O15-delta using a green efficient processing based on spray pyrolysis method. This method is eco-friendly route, which does not generate waste and it allows to obtain nanostructured material with high chemical and structural homogeneity, containing grains with controlled morphology size. Synthesis conditions were optimized to obtain monophasic powders of niobates with TTB-type structure, maintaining an ultrasonic vibration frequency of 1.3 MHz, with precursor solution concentration of 2.5x10-2 mol.L-1 and 5x10-2 mol.L-1, air flow rate ranging of 3 L/min and 5L/min and temperature of 900 °C. The average crystallite size of the powders was at around 9 nm. The powders morphology was analyzed by scanning electron microscopy (SEM) and transmission electronic microscopy (TEM). The increase of the solution concentration (5x10-2 mol.L-1) showed a modification in the particle surface, where a large part of them presented an aspect rough. Furthermore, increasing the nickel concentration in the KSr2Nb5O15 host structure increases the size and the roughness of the particles. This phenomenon suggests that the stoichiometry also modifies the surface of the particle. On the other hand, at low precursor solution concentration (2.5x10-2 mol.L-1) presented smaller and less agglomerated particles with spherical shape and a smooth surface, showing that low concentration of the precursor solution can hold interesting properties, as example, promising catalysts.
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