Dielectric and Raman spectroscopic studies of phase transitions in the (1-x)(Na0.5Bi0.5TiO3)-x(BaSnO3) Lead-free ferroelectric system

Abstract

Ferroelectric materials belonging to perovskite family have attracted the attention of the scientific community from the point of view of fundamental physics and practical device applications. Most of the perovskite materials used for practical device application are lead-based, which are toxic in nature. Therefore, fabrications of lead-free ferroelectric systems have triggered attention of the researchers now-a-days. Among the class of lead-free ferroelectric materials, sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) is a promising candidate due to its high Curie temperature (TC ~ 320 oC), diffuse phase transition and large remnant polarization (Pr ~38 µC cm−2). However, for technological applications of this material, there are several major issues yet to be addressed. These problems of NBT system is because of its (i) high dielectric loss, (ii) high conductivity, (iii) low depolarization temperature (Td), and (iv) high coercive field (73 kV/cm). Recently, some efforts have been carried out to understand the improved ferroelectric behavior of solid solutions of NBT with other ferroelectric perovskites such as BaTiO3, PbTiO3, NaNbO3 etc. However, the solid solution of NBT with BaSnO3 (BS) have been not yet investigated so far. Polycrystalline samples of (1-x) NBT- x BS (x = 0.00, 0.03, 0.05, 0.08, 0.1, 0.12, 0.15) were prepared by a high-temperature solid-state reaction method. The X-ray diffraction, in-situ temperature dependent dielectric and Raman scattering studies were undertaken. Detailed studies of the dielectric properties of the samples were carried out at different temperatures up to 500 oC in the heating run in the frequency range 102 –106 Hz. It was found that the ferroelectric transition temperature (Tc) decreases with increase in BaSnO3 content. From the Raman studies, a compositional driven phase transition ~ x= 0.08 was discernible, matched with X-ray diffraction analysis data. The temperature driven phase transition was obtained for each composition from the temperature dependent Raman spectroscopic studies. These results are discussed and attributed to the length scale of sensitivity of the techniques.