Effect of W substitution in Strontium Bismuth Tantalate Ferroelectric Ceramics: Enhanced Ferroelectric properties
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1250-G16-02
Effect of W substitution in Strontium Bismuth Tantalate Ferroelectric Ceramics: Enhanced Ferroelectric properties Indrani Coondoo1, Neeraj Panwar2 A. M. Biradar1 and A. K. Jha3 1
National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi – 110012
2
University of Puerto Rico, San Juan, Puerto Rico, USA, PR-00931
3
Thin Film and Materials Science Laboratory, Department of Applied Physics, Delhi Technological University, Delhi -110042
ABSTRACT Tungsten (W)-substituted SBT ceramics [SrBi2(Ta1-xWx)2O9 ; 0.0 ≤ x ≤ 0.20] were synthesized by solid state reaction method using different sintering temperatures (1100 οC, 1150 ο C, 1200 οC and 1250 οC). W substitution is found to significantly affect the electrical properties of SBT, including dielectric permittivity, Curie temperature, and ferroelectricity. Dielectric constant ( ε r ) and the Curie temperature (Tc) increase with increasing W content. The dielectric loss reduces significantly with increase in W concentration. The maximum Tc of ~ 390 οC is observed in the sample with x = 0.20 as compared to ~ 320 οC for the pure sample when sintered at 1200 οC. The peak ε increases from ~ 270 in the sample with x = 0.0 to ~ 700 for the composition with x = 0.20, when sintered at 1200 οC. All the tungsten-substituted ceramics have higher 2Pr than that in the pristine sample. The maximum 2Pr (~25 μC/cm2) is obtained in composition with x = 0.05 sintered at 1200 οC. These effects have been interpreted based on the model of the recovery of oxygen vacancies upon W substitution. Such compositions with low loss and high Pr values should be excellent materials for highly stable ferroelectric memory devices. INTRODUCTION Ferroelectrics are exceedingly useful materials in modern technology, with applications such as transducers, actuators, dielectrics, and nonvolatile memories. Among ferroelectrics, it was observed that bismuth oxide layered structures (e.g. SrBi2Ta2O9, BaBi2Ta2O9, SrBi2Nb2O9) originally synthesized by Aurivillius are the most suitable ones for NvRAMs. Since Araujo et. al. [1] reported the fatigue free behavior of SrBi2Ta2O9 (SBT), it has occupied an important position in Pb-free piezoelectrics as well as realization of ferroelectric nonvolatile memories (FeRAM). The crystal structure of SBT consists of (Bi2O2)2+ layers and perovskite-type (SrTa2O7)2units with double TaO6 octahedral layers [2,3]. One interesting feature of the Aurivillius phases resides in the compositional flexibility of the perovskite blocks which allows incorporating various cations for the A- and B-sites. It is thus possible to modify the ferroelectric properties according to the chemical composition. The ferroelectricity arises mainly in the perovskite
blocks; the ferroelectricity is attributed to the rotation and tilting of TaO6 octahedra as well as the off-center displacement of Ta ions in the octahedral unit in SBT [4,5]. Here we report the influence of tungsten (W) substitution and sintering temperature on the dielectric and ferroelectric properties of SBT. EXPERIMENTAL
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