resumo
The glass composition 88SiO(2)-6Li(2)O- 6Nb(2)O(5) (mole%) was successfully prepared by the sol-gel technique. The dried and translucent gel was heat-treated at temperatures between 500 degrees C and 800 degrees C. Lithium niobate crystallites, an important ferroelectric material, were detected in the gel derived glass-ceramics treated above 650 degrees C. In the samples treated at 700 and 800 degrees C the Li2Si2O5 crystalline phase is present. The 800 degrees C treated sample also presents the Li3NbO4 phase. The structure and morphology of the samples were studied by X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The SEM revealed that all the samples, heat-treated above 650 degrees C, present crystallites embedded in the glass matrix. The particles detected in the 600 degrees C treated sample are essentially amorphous, or with an incipient structure. The temperature dependence of the dc electrical conductivity (sigma(dc)) shows two regions with different activation energies. The conductivity behaviour of the sample is mainly due to the mobile ion number. The ac conductivity (sigma(ac)), measured at 1 kHz decreases with the rise of the treatment temperature due to the increase of the LiNbO3 crystallites amount. The electrical behavior of the glass and glass-ceramics reflects the important role carried out by the treatment temperature in the gel-glass structure.
palavras-chave
ELECTRICAL-PROPERTIES; LITHIUM-NIOBATE; CRYSTALLIZATION; BEHAVIOR; LINBO3
categoria
Materials Science
autores
Graca, MPF; da Silva, MGF; Valente, MA
nossos autores
Maria Gracinda Ferreira da Silva
Professor AuxiliarGrupos