Hydrothermal synthesis and dielectric properties of ferroeelctric SrBi 2 Nb 2 O 9 Section B-Research Paper Eur. Chem. Bull. 2013, 2(2), 59-62 59 HYDROTHERMAL SYNTHESIS AND DIELECTRIC PROPERTIES OF FERROELECTRIC SrBi 2 Nb 2 O 9 CERAMICS Hana Naceur [a] , Adel Megriche [a] * and Mohamed El Maaoui [a] Keywords: Hydrothermal synthesis, Dielectric properties, Ferroelectric transition, Ionic conductivity. SrBi 2 Nb 2 O 9 (SBN) compound was synthesized by the hydrothermal method at 220°C for 8h. The dielectric characteristics of ferroelectric SBN ceramic in the 10 Hz – 13 MHz frequency range at various temperatures (300-950 K) have been studied. This study relates initially to measurements of dielectric constant (İ r '), and the dielectric losses (tanį) according to the temperature, as well as the determination of the Curie temperature of SBN. The nature of ferroelectric - paraelectric transition was then deduced. The bulk conductivity of SBN ceramic was performed at different temperatures and the activation energy was calculated. Corresponding Authors e-mail: adel.megriche@fsm.rnu.tn [a] Laboratory of Applied Mineral Chemistry, Department of Chemistry, University Tunis ElManar, Faculty of Sciences, Campus 2092, Tunis, Tunisia Introduction Piezoelectric materials, used in devices working under severe thermal conditions, find applications increasingly. They occupy a very important place in the basic research as well as in electronics and micro-electronics industries. Indeed, such an important research is done nowadays in several fields where high temperature is a decisive parameter. One can quote the use as ultrasonic sensors functioning between 200 and 600 °C for the control in the course of service of equipment in chemical industry, metallurgical or in foundry. They can be also used as accelerometers for the fatigue inspection of the engines of plane or for the heat exchangers in the nuclear reactors. Among materials likely to agree with this type of realisation one finds those containing bismuth layer structure ferroelectric (BLSF) making it possible to reach the field of application until approximately 400 °C. These materials had sufficiently high Curie temperatures to be able to preserve piezoelectric properties 1 . The strontium bismuth niobate SrBi 2 Nb 2 O 9 (SBN) belongs to the Aurivillius phases of perovskite ferroelectrics with general chemical formula (Bi 2 A m-1 B m O 3m+3 ) in which A is a large cation with 12-fold coordination such as (Na, K, Ca, Sr, Ba, Pb, Bi, Ln,…), B is a small cation suitable for 6- fold coordination such as (Fe, Ti, Nb, Mo, W,…) and m is an integer between 1 and 5. The structure consists of (Bi 2 O 2 ) 2+ layers interleaved with perovskite-like (A m- 1 B m O 3m+l ) 2- layers 2 . The basic crystal structure for m = 2, consisting of perovskite (NbO 6 ) octahedra separated at intervals by bismuth oxides (Bi 2 O 2 ) 2+ planes 3 . SrBi 2 Nb 2 O 9 (SBN) is a ferroelectric material having a Curie temperature bordering 691 K. 4 The high Curie temperature makes it among the most promising materials useful for various applications like non-volatile memory (FeRAM), piezoelectric converters 5 - 6 . Many authors were interested in the preparation of SBN ceramics by the conventional solid-solid method 7 - 8 . Nowadays, there is a considerable interest for evaluation of new methods for the functional ceramics synthesis in order to carry out a better control of the physicochemical properties. The way of hydrothermal synthesis has a considerable technological potential due to obtaining nanomaterials at low temperatures of heat treatment 9 - 11 . In this work, SrBi 2 Nb 2 O 9 (SBN) complex solution was synthesized by the hydrothermal way using an autoclave introduced into a controlled furnace, by optimizing the temperature and the thermal processing time. Dielectric measurements were studied. Material and methods The SrNb 2 Bi 2 O 9 (SBN) complex solution was prepared by the hydrothermal way using an autoclave introduced into a controlled furnace. The product obtained was characterised by powder XRD for its phase purity. The XRD powder data was collected using a Bruker D8 Advance model diffractometer in the two theta range 20 – 70°. The resulting powders were added with 1 wt % of polyvinyl alcohol as a binder and compacted into disks (13 mm in diameter and 1 - 2 mm thick) at the pressure of 500 Kg/cm 2 . The disks were supported on Al 2 O 3 setters and sintered at 1100 °C for 2 h in air. Both sides of the ceramics were polished and sputtered with silver to form electrodes. A HP 4192A impedance gain phase analyser was used to measure the dielectric constant as a function of temperature on heating at frequencies of 10 Hz to 13 MHz. These measurements were taken by gradually increasing the temperature between 300 K and 950 K using a Pekly Hermann-Moritz model furnace. The hydrothermal method is a new way of synthesis for ferroelectric materials. The principle of this method consists in introducing the reagents and a solvent into a vessel known as a digestion bomb. The bomb is then heated to increase the pressure. The starting chemicals were commercially available: Sr(NO 3 ) 2 (MERCK, 99%), Bi(CH 3 COO) 3 (INTERCHIM), HCl (PANREAC), CH 3 COOH (FLUKA, 99,5%), NaOH (ACROSS) and NbCl 5