resumo
A transparent glass with the composition 60B(2)O(3)-30Li(2)O-10Nb(2)O(5) (mol%) was prepared by the melt-quenching technique. Glass-ceramics, containing LiNbO3 ferroelectric crystallites, were obtained by heat-treatment (HT) above 500 degrees C, with and without the presence of an external electric field. The dielectric properties of the glass and glass-ceramic were investigated, as a function of temperature (270-315K), in the 10 mHz-32 MHz frequency range. The presence of an external electric field, during the heating process, improves the formation of LiNbO3 crystallites. The rise of the treatment temperature and the applied field, during the heat-treatment, leads to a decrease in the dc electric conductivity (sigma(dc)), indicating a decrease of the charge carriers number. The dielectric permittivity (epsilon') values (300 K; 1 kHz) are between 16.25 and 18.83, with the exception of the 550 degrees C HT sample that presents a epsilon' value of 11.25. An electric equivalent circuit composed by an R in parallel with a CPE element was used to adjust the dielectric data. The results reflect the important role carried out by the heat-treatment and the electric field during the HT in the electric properties of glass-ceramics. (c) 2008 Elsevier B.V. All rights reserved.
palavras-chave
LITHIUM-NIOBATE; CONDUCTIVITY; CRYSTALLIZATION; SYSTEM
categoria
Materials Science
autores
Graca, MPF; da Silva, MGF; Sombra, ASB; Valente, MA
nossos autores
Maria Gracinda Ferreira da Silva
Professor AuxiliarGrupos