Dielectric spectroscopy of LiNbO3 and TmNbO4 nanocrystals embedded in a SiO2 glass matrix

In this paper we present the preparation, by the sol–gel method, of a transparent SiO2:Li2O:Nb2O5 glass doped with Tm3+. The dried gel was heat-treated (HT), in air, at temperatures between 500 and 800 °C. The obtained glasses and glass–ceramics were studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), dc conductivity (σdc), ac conductivity (σac) and by dielectric measurements. The X-ray diffraction patterns show that SiO2 and LiNbO3 crystal phases are present in the samples treated at temperatures above 650 °C. Besides the SiO2 and LiNbO3, TmNbO4 crystal phase was detected in the samples treated above 750 °C. The XRD and SEM show that the average particles size and number increases with the rise of the HT temperature. The electrical and dielectrical properties were related with the glass and glass–ceramics microstructure.