Effect of NaNbO3 crystalline aggregates on the electrical properties of SiO2-Na2O-Nb2O5 glass-ceramics


The presence of NaNbO3 crystallites in a glass matrix has scientific and technological interest due to their electrical properties and potential applications in microwave, pyroelectric and piezoelectric devices. A glass with the composition 60SiO(2)-3ONa(2)O-10Nb(2)O(5) (% mole) was prepared by the melt-quenching method. NaNbO3 microcrystallites were precipitated on the surface of the glass by heat-treatment. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, dc and ac conductivity measurements were used in the study of the glass and glass-ceramic materials. The number of particles, precipitated in the surface of the glass-ceramic samples, increases from the 650 to the 750 degrees C and decrease in the 800 degrees C sample. In all these samples the particles size thickness increases with the rise of the heat-treatment temperature. In the 750 and 800 degrees C samples it was observed the presence of a white surface layer formed by NaNbO3 crystallites aggregations. The dc conductivity (sigma(dc)) decreases with the rise of the heat -treatment temperature up to 750 degrees C and the dielectric constant value, at 1 kHz; and room temperature, has a maximum value of 34.94 for the 800 degrees C treated sample.



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Materials Science


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

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