Solid State Sciences 6 (2004) 333–337 www.elsevier.com/locate/ssscie New ferroelectric and relaxor ceramics in the mixed oxide system NaNbO 3 –BaSnO 3 Abdelhedi Aydi a , Hamadi Khemakhem a , Chokri Boudaya a , Régnault Von der Mühll b,∗ , Annie Simon b a Laboratoire de physique appliquée, faculté des sciences de Sfax, 3018 Sfax, Tunisia b Institut de chimie de la matière condensée de Bordeaux, CNRS, 87, avenue du Dr.A. Schweitzer, 33608 Pessac, France Received 5 December 2003; accepted 11 December 2003 Abstract New ferroelectric or relaxor ceramics were elaborated in the system Ba 1-x Na x Sn 1-x Nb x O 3 (BSNN) by solid-state reaction technique. The effect of cationic substitution of barium for sodium in the A sites and tin for niobium in the B sites in the NaNbO 3 perovskite lattice on symmetry and physical properties were investigated. Room temperature X-ray diffraction and dielectric permittivity in the temperature range from 80 to 600 K with frequencies from 0.1 to 200 kHz, respectively, were used. The material is relaxor with cubic symmetry when x< 0.90 and becomes classical ferroelectric with a tetragonal cell when 0.90  x< 1. Both T C or T m and the maximum of ε ′ r decrease when BaSnO 3 is introduced in the lattice of NaNbO 3 . The plot of T m (f )/T m (1 kHz) versus the logarithm of the frequency allows to determine the limit of composition between the ferroelectric and the relaxor state. Relaxor materials have been obtained at room temperature.  2004 Elsevier SAS. All rights reserved. Keywords: Dielectric; Ferroelectric; Relaxor; Lead-free; Ceramics 1. Introduction The dispersion of a ferroelectric phase like BaTiO 3 in a paraelectric matrix as BaSnO 3 was the first method used by Smolensky co-workers to elaborate dielectric relaxors as early shown in the case of the Ba(Ti 1-x Sn x )O 3 perovskite solid solution [1]. Further investigation on these materials confirms the broadening of the ε ′ r peak at T m and the de- crease of the maximum value of the dielectric permittivity with raising frequency [2]. These materials are of consid- erable interest for applications due to their high value of ε ′ r with a broad thermal variation around T m . Unfortunately, the replacement of Ti 4+ by Sn 4+ involves a steep decrease of T m shifting down the maximum of ε ′ r to low temperature. The purpose of this work was to use NaNbO 3 as fer- roelectric starting material in order to obtain relaxors with higher T m by solid solution with BaSnO 3 . Pure NaNbO 3 is antiferroelectric at room temperature [3,4], however, it has been shown by several authors that it becomes also eas- ily ferroelectric—of course with symmetry change—by low * Corresponding author. E-mail address: rvdm@icmcb.u-bordeaux.fr (R. Von der Mühll). rate substitutions for perovskite compounds like KNbO 3 [5], LiNbO 3 [6] or other [7]. The substituted material shows a relatively high Curie temperature currently higher than 600 K. Solid solutions of BaSnO 3 in NaNbO 3 are obtained by solid state reaction; symmetry and physical properties of ABO 3 perovskite ceramics were investigated by X-ray diffraction and dielectric measurements. Specimens with composition Ba 1-x Na x Sn 1-x Nb x O 3 (x = 0.75, 0.80, 0.85, 0.88, 0.90, 0.95) were elaborated and investigated. 2. Elaboration and ceramic processing The polycrystalline ceramic sample of Ba 1-x Na x Sn 1-x - Nb x O 3 was prepared by conventional solid-state synthesis technique. The starting materials were high-purity (99.9%) powders of BaCO 3 , Na 2 CO 3 , SnO 2 and Nb 2 O 5 . All these materials were dried at 120 ◦ C for 15 h; the powders were then cooled down in vacuum, they were weighed and mixed with ethanol in an agate planetary ball-mill for 60 min. The mixture was heated under oxygen flow at 1100 ◦ C for 12 h. The calcined powder was ball-milled again with deionized 1293-2558/$ – see front matter  2004 Elsevier SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2003.12.006