Effect of Cationic Substitution on Raman Spectra of SrBi 2 Ta 2 O 9 Ceramics and Thin Films

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C3.29.1

Effect of Cationic Substitution on Raman Spectra of SrBi2Ta2O9 Ceramics and Thin Films W. Perez, R. R. Das, P.S. Dobal, Y. I. Yuzyuk, P. Bhattacharya, and R. S. Katiyar Physics Department, University of Puerto Rico, San Juan PR 00931-3343 ABSTRACT In the present work micro-Raman spectroscopy has been used to understand the lattice dynamics of cation substituted SBT ceramics and thin films. Different concentrations of Ca and V were introduced into SBT lattices. Incorporation of Ca ion at Sr-site was confirmed by decrease in the lattice parameters calculated from x-ray diffraction data. The lowest Raman modes at 27 cm-1 and 58 cm-1 showed upward shift with increasing Ca concentration and was attributed to the lower mass and lower ionic radii of Ca. The temperature dependant Raman studies revealed the increase of the phase transition temperature with increased Ca content, and was attributed to the decrease in tolerance factor. Substitution of smaller cation at Sr site in SBT compound has increased lattice mismatch between SrO and TaO2 planes inside the stable perovskite unit of SrTa2O7 which has pronounced influence on ferroelectric properties of SBT. Substitution of vanadium at Ta-site of SBT did not influence the low frequency Raman modes of SBT. However, it showed a pronounced influence on the O-Ta-O stretching modes by splitting the mode frequency at 810 cm-1. The transition temperature of SBT was reduced with increasing vanadium contents. INTRODUCTION Ferroelectric thin films of Aurivillius layered compounds have drawn much attention for future non-volatile random access memory (NVRAM) devices [1,2]. In particular, SrBi2Ta2O9 (SBT) thin films showed excellent fatigue free characteristics in combination with the low leakage current density (