J MATER SCI 41 (2006)1137–1144 The electric behavior of a lithium-niobate-phosphate glass and glass-ceramics M. P. F. GRAC ¸ A, M. A. VALENTE Departamento de F´ ısica, Universidade de Aveiro, 3800-193 Aveiro, Portugal M. G. FERREIRA DA SILVA Departamento de Engenharia Cer ˆ amica e do Vidro (CICECO), Universidade de Aveiro, 3800-193 Aveiro, Portugal Published online: 4 February 2006 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 ◦ 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 LiNbO 3 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 LiNbO 3 ferroelectric crystals present in the glass-ceramics and the dielectric constant values. C  2006 Springer Science + Business Media, Inc. 1. Introduction In recent years there has been a considerable amount of in- terest in the preparation, and study of the physical proper- ties, of glass-ceramics with ferroelectric crystalline phases [1]. An important ferroelectric material is lithium niobate, LiNbO 3 , due to its excellent pyroelectrical, piezoelectrical and photorefractive properties [2–4]. This material has a high Curie temperature, T c = 1210 ◦ C[3, 5]. However, the usual preparation of LiNbO 3 crystals, by the Czochralski method, is time consuming, very expensive and with Li deficiency crystals [1, 2, 6]. Glass-ceramics, with the ferroelectric crystal phase, seems to be an interesting al- ternative due to its relative low preparation time and costs. The purpose of the present study is to prepare glass-ceramics containing LiNbO 3 crystals. An attempt has been made to establish a correlation between the electrical properties of the glass and glass-ceramics and their microstructure. 2. Experimental procedures A glass with the composition 50Li 2 O-40P 2 O 5 -10Nb 2 O 5 (mol%) was prepared using the melt-quenching method. The glass was prepared from the reagent grade lithium carbonate (Li 2 CO 3 - Merck), ammonium dihydrogen phosphate (NH 4 H 2 PO 4 - Merck) and niobium oxide 0022-2461 C  2006 Springer Science + Business Media, Inc. DOI: 10.1007/s10853-005-3652-6 1137