Int. J. Nanoelectronics and Materials 2 (2009) 137-145 X-ray and dielectric studies of ferroelectric phase in the Ba 1-x (Yb 0.5 Na 0.5 ) x TiO 3 system for low doping level L. Khemakhem 1,2* , I. Kriaa 2 , M. Derbel 2 , N. Abdelmoula 2 1 Laboratoire des Sciences des Matériaux et Environnement, Faculté des Sciences de Sfax, B.P. 802, 3018 Sfax, Tunisie. 2 Laboratoire des Matériaux Ferroélectriques, Faculté des Sciences de Sfax B.P. 802, 3018 Sfax, Tunisie. Abstract Ceramics of solid solution Ba 1-x (Yb 0.5 Na 0.5 ) x TiO 3 were sintered in the temperature range 1220-1400°C. Dielectric properties of ceramics belonging to the whole composition domain were investigated in a broad range of temperatures (75-450 K) and frequencies (0.1-100 kHz). These ceramics were prepared using the conventional mixed-oxide technique. The temperature dependence of the dielectric constant of these ceramics were investigated. The rombohedral–orthorhombic and orthorhombic-quadratic perovskite transitions are characterized by two weak peaks but the tetragonal-cubic or ferroelectric- paraelectric one is characterized by a pronounced peak with weak frequency dispersion. Excellent dielectric properties have been obtained. The single phase of these prepared ceramics was characterizedby X-ray diffraction. Keywords: Perovskite; Lead-free ceramics; Dielectric; Ferroelectric; Relaxor. PACS: 77.84.Lf; 77.84.Dy; 77.22.Ch; 77.80.Bh; 77.22.Gm. 1. Introduction According to their behavior, the ferroelectric materials with perovskite-like structure may be divided into different classes depending on whether they are classical or relaxor ferroelectris [1]. Relaxor materials are characterized mainly by frequency dispersion and broad peaks in the dielectric susceptibility versus temperature [2]. Many investigations have been devoted to the study of the relaxation parameters in order to achieve their use in satisfactory capacitors and actuators [3]. The relaxor behavior was mainly obtained in lead- based ceramics for examples PbMg 1/3 Nb 2/3 O 3 and derived compounds [4, 5]. However, these materials have a drawback due to the volatility and the toxicity of PbO. Up to now, current research is oriented to environment friendly applications using lead-free materials [6–8]. Ceramics based on barium titanate (BaTiO 3 ) are frequently used to manufacture multilayer ceramic capacitor and thermistors owing to their high dielectric constant [9]. Barium titanate (BaTiO 3 ) is the most common ferroelectric oxide in the perovskite ABO 3 structure [10]. In BaTiO 3 a phase transition occurs from rhombohedra (C3v) to cubic (Oh) through orthorhombic (C2v) and tetragonal (C4v) as temperature increases to about 400 K. * ) For Correspondence, E-mail: khemakhemimmea2009@yahoo.fr