The dielectric behavior of a thermoelectric treated B 2 O 3 –Li 2 O–Nb 2 O 5 glass M.P.F. Grac ßa a , M.G. Ferreira da Silva b , A.S.B. Sombra c , M.A. Valente a, * a Physics Department (I3N), Aveiro University, 3800-193 Aveiro, Portugal b Glass and Ceramic Engineering Department (CICECO), Aveiro University, 3800-193 Aveiro, Portugal c Physics Department (LOCEM), Ceará Federal University, Campus do Pici, Postal Code 6030, 60455-760 Fortaleza, Ceará, Brazil article info Article history: Received 31 January 2008 Available online 3 May 2008 PACS: 63.50 72.20 77.22 77.84 Keywords: Glass–ceramics Conductivity Dielectric properties, relaxation, electric modulus Thermally stimulated Depolarization current abstract A transparent glass with the composition 60B 2 O 3 –30Li 2 O–10Nb 2 O 5 (mol%) was prepared by the melt- quenching technique. Glass–ceramics, containing LiNbO 3 ferroelectric crystallites, were obtained by heat-treatment (HT) above 500 °C, with and without the presence of an external electric field. The dielec- tric properties of the glass and glass–ceramic were investigated, as a function of temperature (270– 315 K), in the 10 mHz–32 MHz frequency range. The presence of an external electric field, during the heating process, improves the formation of LiNbO 3 crystallites. The rise of the treatment temperature and the applied field, during the heat-treatment, leads to a decrease in the dc electric conductivity (r dc ), indicating a decrease of the charge carriers number. The dielectric permittivity (e 0 ) values (300 K;1 kHz) are between 16.25 and 18.83, with the exception of the 550 °C HT sample that presents a e 0 value of 11.25. An electric equivalent circuit composed by an R in parallel with a CPE element was used to adjust the dielectric data. The results reflect the important role carried out by the heat-treatment and the electric field during the HT in the electric properties of glass–ceramics. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction In recent years there has been a considerable amount of interest in the preparation and study of the physical properties of ferroelec- tric nanoparticles embedded in glass matrices [1,2]. The main advantage of a glass matrix, as a host for the ferroelectric crystal- lites, is its lower level of porosity when compared with that of the ceramics and the possibility of engineering their microstruc- ture by controlling the number and sizes of crystallites. Lithium niobate (LiNbO 3 ) is an important ferroelectric material due to its excellent pyroelectric, piezoelectric and photorefractive properties [3,4] and it is used for the fabrication of active waveguides, modu- lators, and switches for application in integrated optical circuits [5]. The correlation between the electrical and dielectrical properties of the 60B 2 O 3 –30Li 2 O–10Nb 2 O 5 (%mol) glass and glass– ceramics containing LiNbO 3 crystallites, obtained through heat- treatments with and without the presence of an external electric field, and their microstructures was the main purpose of this work. 2. Experimental A colorless and transparent glass, with the 60B 2 O 3 –30Li 2 O– 10Nb 2 O 5 molar composition was prepared by melt-quenching. The reagents (B 2 O 3 ; Li 2 CO 3 ; Nb 2 O 5 ), in the appropriate amounts, were mixed for 1 h, in an agate ball-mixing planetary system. The mixture was heated in a platinum crucible at 700 °C, for 2 h (to remove the CO 2 from the Li 2 CO 3 ) and melted at 1100 °C for 30 min. The molten material was quenched between two stainless steel plates. The as-prepared sample was heat-treated (HT) at 450, 500 and 550 °C. These temperatures were chosen in agreement with the differential thermal analysis result of the as-prepared sample [6]. Thermoelectric treatments (TET) were also performed, at 500 °C applying 50 kV/m (500B sample) and 100 kV/m (500C sample) [6]. The X-ray diffraction patterns were obtained at room tempera- ture, using bulk samples, in a Philips X’Pert system, with a Ka radi- ation (k = 1.54056 Å) at 40 kV, and 30 mA, with steps of 0.05° and a time per step of 1 s. The scanning electron microscopy (SEM) was performed in a Philips XL 30 system on the surface and fracture sur- face of the samples (covered with gold before microscopic observation). 0022-3093/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2008.03.007 * Corresponding author. E-mail address: mav@fis.ua.pt (M.A. Valente). Journal of Non-Crystalline Solids 354 (2008) 3408–3413 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol