A preliminary study of dielectric properties and structures of NBT-SCN system

Abstract

It is well known that a number of compounds with perovskite structure display very good ferroelectricity. Barium titanate and Lead titanate are typical examples of this family. Nevertheless, pure BaTiO3 or PbTiO3 has been rarely used in practical applications and substitutions in the form of solid solution or even morphotropic phase boundary (MPB) have been taken to improve the dielectric, piezoelectric and pyroelectric properties. Furthermore, to avoid pollution during sintering process lead-free or low lead content ferroelectric materials have recently attracted interests. Therefore, Bismuth sodium titanate, (Na,,2 Bil ,:)TiO3(abbreviated NBT),El'2]based solid solutions have been intensively studied and some of them showed attractive application prospect, c_3.4? In the present paper,dielectric properties and structural changes in the (Na l , eBi l ' , )T iO3-Sr (Cul :~Nb, :,)():~(SCN) system are studied which is a new group of lead-free ferroelectric materials. Conventional ceramic fabrication techniques were employed to prepare NBT-SCN ceramics. Chemical powders with high purity ( ~ 9 9 ~ ) of Bie()3 ,CuO,TiOz ,NbeOs,NaCO3 and SrCOa were used as the starting raw materials. Specimens of compositions of (1 x )NBT-xSCN with x = 0, 0 .2 ,0 . 4 ,0 . 6 ,0 . 8, and 1. 0 were studied. The powders mixed by ball-milling were calcined at temperatures between 950C and 1 200C for about 6 h. Then some of the compositions were ball-milled and calcined again in order that a single phase with perovskite structure could be obtained. The phase identification was carried out by X-ray diffraction (XRD) at room temperature. Then ceramic powders were pressed into discs of 13 mm in diameter and about 1. 5 mm in thickness. The disc samples were sintered at temperatures between 1 175 C and 1 300 (" for about 6 h in an air atmosphere. The detailed sintering temperatures are listed in Table 1. At last ,fired silver paste was used as the electrode for the dielelctric measurement.