J Electroceram (2006) 16:393–398 DOI 10.1007/s10832-006-9886-0 Phase transition and electrical studies of wolframium doped SrBi 2 Ta 2 O 9 ferroelectric ceramics Indrani Coondoo · A. K. Jha · S. K. Agarwal · N. C. Soni C  Springer Science + Business Media, LLC 2006 Abstract In this study, crystalline structure, dielectric and impedance properties of SrBi 2 Ta 2 O 9 (SBT) - based fer- roelectric ceramics have been investigated with the sub- stitution of wolframium/tungsten (W) onto the tantalum site. Wolframium doped SrBi 2 (W x Ta 1−x ) 2 O 9 (0.0 ≤ x ≤ 0.20) ceramics were synthesized by solid state reaction method. The X-ray diffractogram analysis revealed that the substitution formed a single phase layered perovskite structure for the doping content up to x ≤ 0.05. The di- electric measurements as a function of temperature show an increase in Curie temperature (T c ) over the composi- tion range of x = 0.05 to 0.20. The W 6+ substitution in perovskite-like units results in a sharp dielectric anomaly at the ferroelectric phase transition. Furthermore, the di- electric constant at their respective Curie temperature in- creases with wolframium doping. Both enhanced Curie tem- peratures and dielectric constants at the Curie points in- dicate an increase in polarizability, which could be at- tributed to the increased “rattling space” due to the incor- poration of the smaller tungsten cations. The dielectric loss reduces significantly with tungsten addition. AC impedance properties vis-` a-vis wolframium content has also been studied. Keywords Aurivillius . Dielectric properties . Strontium bismuth tantalate . Impedance analysis I. Coondoo · A. K. Jha () Department of Applied Physics, Delhi College of Engineering, Delhi-110042, India e-mail: akj6467@indiatimes.com S. K. Agarwal · N. C. Soni National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi-110012, India 1 Introduction The family of mixed bismuth oxides with general formula [Bi 2 O 2 ] 2+ [A n−1 B n O 3n+1 ] 2− was first studied by Aurivillius [1–4]. Their structures comprise intergrowths of [Bi 2 O 2 ] 2+ layers with perovskite [A n−1 B n O 3n+1 ] 2− layers (n = 1, 2, 3, 4). Among the bismuth layered structure ferroelectrics (BLSFs), SrBi 2 Ta 2 O 9 (SBT), SrBi 2 Nb 2 O 9 (SBN) and their solid solutions are the best candidates for application in information data storage such as ferroelectric random access memories (FeRAMs). They offer several advantages, being lead-free, fatigue—free and having independence of ferro- electric properties with film thickness, as compared with isotropic perovskite ferroelectrics such as Lead Zirconium Titanate (PZT) [5–7]. Understanding of these perovskite ferroelectric materials in respect of their A- and B - site substitutions, which af- fects their physical and chemical properties is known. This effect has been extensively exploited in piezoelectrics and ferroelectrics to improve their performance [8–14]. Most of the research effort on the improvement of the dielectric and ferroelectric properties are based on the A-site substi- tutions in SBT. However, the authors could find only lim- ited work on the dielectric and ferroelectric properties of the layered perovskite, SBT, through substitution of the B -site ions (Ta 5+ ) with other alternate cations of higher oxidation state. Various doping ions, such as La 3+ , Nd 3+ and Nb 5+ in PZT result in enhanced remnant polarization and a de- creased coercive field [15–16]. Similar results were obtained in SBN ferroelectric ceramics through partial substitution of Nb 5+ by V 5+ [17, 18]. Thus doping SBT with smaller wol- framium (W 6+ ) for tantalum (Ta 5+ ) could be an approach for improving the dielectric and ferroelectric properties of SBT. Springer