|08-094||Marco Aurélio Oliveira||Oliveira, M.A.(Universidade Federal de Uberlândia); M'Peko, J.(University of São Paulo); Hernandes, A.C.(Universidade de São Paulo); de los Santos Guerra, J.(Universidade Federal de Uberlândia); Mendez-González, Y.(Universidad de La Habana);||
The present work aims the investigation of the physical properties of barium titanate () based ceramics, considering the addition of donor elements in the A- and B-sites of the perovskite () structure. Ceramic samples were synthesized from the polymeric precursor method (PPM), according to the chemical formula () and (), where = 0.001, 0.002, 0.003, 0.004 and 0.005. The desired ferroelectric phase was confirmed from XRD technique for all the studied samples. The microstructural properties revealed a decrease in the grain-size with the increase of the Gd content for the system, being this behavior related to the pinning-effect promoted by the inclusion of the rare-earth element in the grain-boundary region. On the other hand, an increase in the grain-size was observed for the samples up to the composition and then decreases for higher Nb concentrations. This anomaly has been attributed to microstructural defects promoted by induced Ti vacancies for higher Nb ion concentration. Very high values for the dielectric permittivity were verified in the dielectric properties for both Gd- and Nb-modified (BT) samples, when compared to those reported for the pure BT system, which could be associated with the presence of conductive mechanisms. Those conductive-mediated responses can be confirmed by the strong dielectric dispersion observed in both and systems. The experimental results were analyzed from the Cole-Davidson´s relaxation function revealing two contribution for the electrical conduction: (i) a polaron-type conduction mechanism for the system and (ii) a -type charge carriers hopping mechanism for the samples.
The authors would like to thank to FAPEMIG, FAPESP and CNPq Brazilian agencies for financial support. M. A. Oliveira also thanks the PPGCM, UNESP, Ilha Solteira, Brazil.