The electric behavior of a lithium-niobate-phosphate glass and glass-ceramics


A glass with a composition of 50Li(2)O-40P(2)O(5)-10Nb(2)O(5) (% mol) was prepared by the melt-quenching method and heat-treated in air between 450 and 500 degrees C. The samples were studied using X-ray powder diffraction (XRD), density measurements, Raman spectroscopy, scanning electron microscopy (SEM), dc electrical conductivity (adc) and dielectric measurements. The LiNbO3 crystalline phase was detected in the samples heat-treated at 480 and 500 degrees C. The dc conductivity, at 300 K, decreases and the activation energy increases with the rise of the heat-treatment temperature. The dielectric data between 1 Hz and 100 kHz, at room temperature, were studied using the impedance formalism (Z*). These results show the existence of a relaxation mechanism, probably associated with a distribution of relaxation times. The mean value of the relaxation time, tau(sigma) increases with the rise of the heat-treatment temperature. The fit of the dielectric data with a complex nonlinear least squares algorithm (CNLLS), reveals that a resistor A, in parallel with a constant phase element (CPE, Z(CPE) = 1/[Y-0(j w)(n)]), is a good equivalent circuit. The R-value has a maximum for the sample heat-treated at 480 degrees C, and the n parameter has the inverse behavior. The Y-0 parameter decreases with the increase of the heat-treatment temperature. The dielectric constant value, at 1 kHz and room temperature, increases from 39.98 up to 97.80 with the rise of the heat-treatment temperature. These results suggest that exists a relation between the number of LiNbO3 ferroelectric crystals present in the glass-ceramics and the dielectric constant values. (c) 2006 Springer Science + Business Media, Inc.



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Materials Science


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

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