Caracterização dielétrica da cerâmica ferroelétrica Ti0.4Fe0.3Nb0.3O2 (TFNO) com adição de Bi2O3

Abstract

From of the powder oxides, Fe2O3 (Sigma-Aldrich, 99.0%), Nb2O5 (Sigma-Aldrich, 99.99%) and TiO2 (Vetec, 99.8%), was done synthesis, by solid state reaction method of the Ti0.4Fe0.3Nb0.3O2 (TFNO) ceramic. Following the stoichiometric proportions the mixed oxides were ball milled for 7h and calcined at 1075°C for 4h. TFNO phase was confirmed from X-ray diffraction technique (XRD) and Rietveld refinement. Then, were made additions of 4% wt Bi2O3 to the calcined powder. Thence forward 0,86 grams of the TFNO calcined samples and a same amount with 4% wt Bi2O3 were shaped at a pressure of 200MPa which resulted in two discs of ~17,69 mm of diameter and ~0,93 mm of thickness. The samples were sintering at 1125°C for five hours. After sintering her were submitted at analysis by XRD and impedance spectroscopy study. The X-ray diffraction technique confirmed a rutiletype structure [TiO2 (tP6)] to calcined powder and to presence of two phases, Ti0.4Fe0.3Nb0.3O2 (TFNO tetragonal rutile P 42/m n m(136)) and Bi1.721Fe1.056Nb1.134O7(BFNO cubic F d -3 m Z(227)), for sample sintered with 4% wt Bi2O3. Conductivity analysis has been carried out and showed a low-frequency constant conductivity and a high-frequency nearly Debye-like transition which is associated with the fact that the transport processes are strongly perturbed in a grain and grain boundary, i.e., variation in frequency can be understood by the existence of ionic conduction. High conductivity values observed may be related to oxygen vacancies which can cause valence floating of iron ions (+3 state to the +2 state).