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

A glass with a composition of 50Li2O-40P2O5-10Nb2O5 (% mol) was prepared by the melt-quenching method and heat-treated in air between 450 and 500◦C. The samples were studied using X-ray powder diffraction (XRD), density measurements, Raman spectroscopy, scanning electron microscopy (SEM), dc electrical conductivity (σdc) and dielectric measurements. The LiNbO3 crystalline phase was detected in the samples heat-treated at 480 and 500◦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, τ σ , 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 (R), in parallel with a constant phase element (CPE, ZCPE = 1/[Y0(jw)n]), is a good equivalent circuit. The R-value has a maximum for the sample heat-treated at 480◦C, and the n parameter has the inverse behavior. The Y0 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.