Structural and electrical properties of SiO2–Li2O–Nb2O5 glass and glass-ceramics obtained by thermoelectric treatments

Glass and glass-ceramics with the molar composition of 60SiO2–30Li2O–10Nb2O5 (mole %) were studied. Ferroelectric lithium niobate (LiNbO3) nanocrystals were precipitated in the glass matrix trough a thermal treatment, with and without the simultaneous application of an external electric field. The as-prepared sample, yellow and transparent, was heat-treated (HT) at 600 and 650 C and thermoelectric treated (TET) at 600 C. The applied electric fields were the following ones: (i) 5 · 104 V/m; (ii) 1 · 105 V/m. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and dielectric spectroscopies were used to investigate the glass samples properties. The LiNbO3 crystalline phase was detected in the 650 C HT sample and in the 600 C TET samples. The presence of an external electric field, during the heating process, promotes the glass crystallization at lower temperatures. In the TET samples, the surface crystallization of the cathode and the anode are different. The number and size of the crystallites, in the glass network, dominate the electrical dc behavior while the ac conductivity process is more dependent of the glass matrix structure. The obtained results reflect the important role carried out by the temperature and the applied electric field in the glass-ceramic structures