Improved BaBi4Ti4O15 Relaxor Ferroelectrics for FRAM Application

Abstract

Bi-based Aurivillius family of compounds have received considerable attention as the materials for ferroelectric random access memory (FRAM) because of their low operating voltage, fast switching speed, large remnant polarization, low coercive field, superior polarization fatigue resistant characteristics and high Curie temperature. A large remnant polarization, low coercive field and high Curie temperature are required for better performance of FRAM devices. Majority of Aurivillius oxides are normal ferroelectrics, while only a few of them such as BaBi2Nb2O9, BaBi2Ta2O9, BaBi4Ti4O15 etc. exhibit relaxor behaviour. Relaxor ferroelectrics are attractive for a wide range of applications owing to their excellent high dielectric and piezoelectric responses over a wide range of temperatures. Ferroelectric properties of these compounds are often improved by chemical lattice site engineering. This is done by suitable atomic substitutions at ‘A’ and/or ‘B’ of the structure. Nb5+ substitution at ‘B’ site has been proved to be an most effective site engineering in 2 and 3 layered compounds. In the present study, Nb5+ has been substituted at ‘B’-site and Na1+ at ‘A’-site to compensate charge in the formulation Ba1-xNaxBi4Ti4-xNbxO15. Effect of the substitution on the structural, microstructural, dielectric and ferroelectric properties were evaluated. The AC complex impedance spectroscopy was used to analyze the change in dielectric conductivity of the ceramics. An improved permittivity, increased remnant polarization and decreased coercive field were found in the Nb-substituted compound.