Caracterização dielétrica de partículas nanométricas e nanoestruturadas de óxido de niobato da família tetragonal tungstênio bronze com estequiometria KSr2Nb5O15

Abstract

This work aimed the study of “size effect” through permittivity measurements of nanometric particles and/or nanostructured of niobate oxide KSr2Nb5O15, a ferroelectric oxide belonging to the tetragonal tungsten bronze family (TTB). Determination of nanoparticles dielectric constant was done using the mixture technique. In this technique, nanoparticles of unknown dielectric permittivity are dispersed in a medium of known dielectric permittivity. From the dielectric response of the mixture, the dielectric permittivity of the nanoparticles is calculated using numerical modeling by means of equivalent circuits. The KSr2Nb5O15 phase was prepared using a chemical route (polyol modified method) and the optimization of the temperature calcination was performed aiming to obtain nanoparticles and the resulting nanostructured particles were evaluated. The structural characterization was carried out by X-ray diffraction (XRD), infrared absorption spectroscopy (FTIR) and UV-Vis spectroscopy allowing the evaluation of cell parameters, relative crystallinity and crystallite size, unitary cell volume and gap energy. The impedance spectroscopy technique in the range from 5 Hz to 3 MHz to study dielectric properties of samples was used. The presence of ferroelectric phase in samples was confirmed and the size effect was identified on nanoparticles.