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

Author： Graça M. Valente M. Ferreira Da Silva M.

ISSN： 0022-2461

Source： Journal of Materials Science, Vol.41, Iss.4, 2006-02, pp. : 1137-1144

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Abstract

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 (σ_dc) 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, Z _CPE = 1/[Y ₀(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 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.