Structural and electrical characteristics of LiNbO3 embedded in a 34% SiO2 glass matrix


Lithium niobate (LiNbO3) is a ferroelectric crystal and has attracted great attention due to its excellent piezoelectric, piroelectric, electrooptic, acustooptic and photorefractive properties. Recently, due to its electro-optical applications, a considerable interest has been shown in the preparation and study of its properties when embedded in a glass structure. In this work, we present the preparation of the glass composition 34SiO(2)-33Li(2)O-33Nb(2)O(5) (mol%), by the melt-quenching method. The as-prepared sample, yellow and transparent, was heat-treated at 550, 575, 600 and 700 degrees C (HT) and at 575 degrees C with an electric field applied (thermoelectric treatment - TET). The applied electric fields were: (A) 100 kV/m; (B) 250 kV/m; (C) 500 kV/m. The glasses and glass-ceramics were studied by differential thermal analysis (DTA), X-ray power diffraction (XRD), scanning electron microscopy (SEM), dc conductivity (sigma(dc)) ac conductivity (sigma(ac)), dielectric and thermally stimulated depolarization current (TSDC) measurements. LiNbO3 crystal phase was detected, by XRD, in the samples treated without electric field applied, at temperatures above 575 degrees C. The increase of the electric field amplitude, applied during the thermal treatment, lead to the formation of a white layer in the sample surface in contact with the positive electrode during the heat-treatment. The sigma(dc)or sigma(ac) and the dielectric constant decrease with the rise of the treatment temperature. The presence of an electric field, during the HT process, seems to promote the growing of LiNbO3 Particles in a preferential crystal orientation, jusfifying the observed increase of the epsilon' values in the TET samples. The Z '' versus Z ' plot shows a semi-arc for all samples, with the exception of the sample 600 HT whose Z '' frequency dependence is linear. The semi-arcs were fitted with a R(R//CPE)(ReHCPe) equivalent circuit, using a CNLLS algorithm. The thermally stimulated depolarization current measurements show the presence of two depolarization current peaks in all HT samples. The electrical and dielectrical behaviour, of the glass materials, shows the important role carried out by the heat-treatment conditions in the glass structure. (c) 2007 Elsevier Ltd. All rights reserved.



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Materials Science


Graca, MPF; da Silva, MGF; Valente, MA

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