resumo
The aim of this research is the study of the structural, morphological and electrical properties of a 44SiO2-33Li2O-23Nb2O5 (mol%) glass and glass-ceramics. XRD, SEM, Raman and dielectric spectroscopy and (Thermally stimulated DC) TSDC measurements were used to characterize the samples. The LiNbO3 crystalline phase was detected, by XRD and Raman spectroscopy, in the samples treated above 873 K. The volume ratio of the particles increases with increase in heat-treatment temperature. The behavior of the sigma(dc) and sigma(ac), with the increase of the heat-treatment (HT) temperature, was related with the decrease of the free ions number in the glass matrix and consequent increase of the volume ratio between the LiNbO3 crystalline phase and the glass matrix. The epsilon' value decreases with the increase of the HT temperature. The complex impedance spectra were fitted to a equivalent electric circuit. The Z '' vs. Z' plots of the samples HT below 873 K, indicate the existence of a distribution of relaxation times. The TSDC measurements revealed the presence of three depolarization peaks in the as-prepared and 550HT treated sample. The sample HT575 presents two TSDC peaks, and the samples HT600 and HT650 one TSDC peak. These peaks were correlated with the structure and mobility of ions in the prepared glass and glass-ceramics. The behavior of the dc and ac conductivities, TSDC peaks and dielectrical characteristics reflect the important role carried out by the treatment temperature in the formation of a glass ceramic structure. (c) 2007 Elsevier B.V. All rights reserved.
palavras-chave
THERMALLY STIMULATED POLARIZATION; SILICATE-GLASSES; RAMAN-SPECTROSCOPY; LITHIUM-NIOBATE; ION MOTION; CRYSTALLIZATION; SPECTRA; ORIGIN
categoria
Materials Science
autores
Graca, MPF; da Silva, MGF; Sombra, ASB; Valente, MA
nossos autores
Maria Gracinda Ferreira da Silva
Professor AuxiliarGrupos