Electrical and dielectrical properties of SiO2–Li2O–Nb2O5 glass and glass-ceramics obtained by thermoelectric treatments

doi:10.1016/j.jnoncrysol.2006.02.172

Journal of Non-Crystalline Solids

Volume 352, Issues 42–49, 15 November 2006, Pages 5199-5204

https://doi.org/10.1016/j.jnoncrysol.2006.02.172 Get rights and content

Abstract

The electrical and dielectrical properties of the glass and glass-ceramics with the 60SiO₂–30Li₂O–10Nb₂O₅ (mole%) composition, containing LiNbO₃ crystallites, were studied. The dc electric conductivity (σ_dc) and dc activation energy (E_a(dc)) decreases with the rise of the heat-treatment (HT) temperature and with the increase of the amplitude of the applied electric field. The highest dielectric constant, 48.19, was observed in the 650HT sample. The dielectrical properties were discussed through a three serial capacitor model, two related with the sample surfaces and one with the bulk material, showing that the bulk has the major contribution for the dielectrical characteristics. A resistance in parallel with a constant phase element (CPE) is the best equivalent circuit that describes the dielectrical behavior. The obtained results reflect the important role carried out by the treatment temperature and the applied electric field in the electrical and dielectrical properties of the glass.

Introduction

The study of the physical properties of glass-ceramics with ferroelectric crystallites has been achieved, a considerable amount of interest, in the past years, due to their electrical, dielectrical and electro-optic properties and technological applications [1]. Lithium niobate (LiNbO₃) is an important ferroelectric material due to its excellent pyroelectrical, piezoelectrical, photorefractive properties [1], [2] and optoelectronic applications [3], [4]. glass-ceramics, containing the ferroelectric crystalline phase, have technological interest due to its relative low preparation time and costs. Thus the study of the glass systems: SiO₂–Li₂O–Nb₂O₅, P₂O₅–Li₂O–Nb₂O₅ and B₂O₃O–Li₂O–Nb₂O₅, with ferroelectric phases, were recently been shown [5], [6], [7], [8], [9], [10], [11], [12].

The change of the electrical and dielectrical properties of the 60SiO₂–30Li₂O–10Nb₂O₅ (mole%) glasses and glass-ceramics with the heat treatment conditions was the main purpose of this work.

Section snippets

Experimental

The 60SiO₂–30Li₂O–10Nb₂O₅ (mole%) transparent and yellow glass was prepared by the melt-quenching technique. The reagents (SiO₂, Li₂CO₃ and Nb₂O₅), in the appropriate amounts, were melted in a platinum crucible at 1450 °C for 30 min and quenched, to room temperature, into a clean stainless steel plate and pressed by another, to obtain flat samples. The as-prepared glass has been heat-treated (HT) in air, at 600 °C and 650 °C, with a heating rate of 75 °C/h, during 4 h.

The thermoelectric treatments

Results

The LiNbO₃ crystalline phase was detected by XRD in the 650 °C HT and in the 600 °C TET samples (Fig. 1) [13]. However, particles were observed, by scanning electronic microscopy (SEM) in the transparent 600HT sample, (Fig. 2(a)), with an average size of 1 μm approximately, but were not detected by XRD. This is an indication of the amorphous or incipient crystallization nature of these particles [14]. The SEM shows that the rise of the HT temperature increases the amount of the particles present

Discussion

In the 60SiO₂–30Li₂O–10Nb₂O₅ (mole%) glass and glass-ceramics, with LiNbO₃ and Li₂Si₂O₅ crystallites, the dc conductivity (σ_dc, Table 1) decrease with the rise of the HT temperature. This behavior can be assigned to the decrease of the number of network modifiers and consequent increase of the volume ratio between the LiNbO₃ plus Li₂Si₂O₅ crystalline phases and the glass matrix (Fig. 1, Fig. 2). It should be noticed that in these glasses, was detected, by Raman spectroscopy, the presence of

Conclusions

The electrical conduction process, in the 60SiO₂–30Li₂O–10Nb₂O₅ (mole%) glass and glass-ceramics, is dominated by the charge carriers number.

The increase of ε′ and of τ_Z, with the rise of the HT temperature, was assigned to the increase of the volume ratio between the crystalline phases and the glass matrix. In the TET samples the ε′ behavior was assigned to the bulk material characteristics.

The dielectric theoretical fit reveals that a resistance in parallel with a CPE element is an equivalent

Acknowledgement

The authors thank to the Fundação para a Ciência e Tecnologia (FCT), for the financial support (SFRH/BD/6314/2001).

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Electrical and dielectrical properties of SiO2–Li2O–Nb2O5 glass and glass-ceramics obtained by thermoelectric treatments

Abstract

Introduction

Section snippets

Experimental

Results

Discussion

Conclusions

Acknowledgement

J. Non-Cryst. Solids.

Mat. Sci. Eng. A

J. Non-Cryst. Solids

J. Non-Cryst. Solids

J. Non-Cryst. Solids

J. Non-Cryst. Solids

Solid State Ionics

J. Non-Cryst. Solids

J. Non-Cryst. Solids

Mater. Res. Bull.

Solid Sate Ionics

J. Am. Ceram. Society

J. Am. Ceram. Society

Electrical and dielectrical properties of SiO₂–Li₂O–Nb₂O₅ glass and glass-ceramics obtained by thermoelectric treatments