RAMAN STUDY OF FERROELECTRIC BARTUM BISMUTH TITANATE

Abstract

Barium bismuth titanate, BaBi4Ti4O15 has been extensively studied for its feroelectric and other excellent properties. BaBi4Ti4O15 is a candidate material for high temperature piezoelectric applications, memory storage, and optical displays because of its high Curie temperature and electro-optical properties. This family of bismuth oxides, discovered more than 60 years ago by Aurivillius [1]. The structure of the Aurivillius family of compounds consist of (Bi2O2)2+ layers interleaved with perovskite-like (An-1BnO3n+3)2- layers. BaBi4Ti4O15 as the n = 4 member of the Aurivillius family has Ba ions at the I sites and Ti ions at the .B sites of the perovskite (An-1BnO3n+3)2- block ((Bi2O2)2- .((BaBi4Ti4O15)2-) (Fig. 1). It has a high Curie temperature of 417 C [2]. The crystal structure of BaBi4Ti4O15 can be described by an orthorhombic or a pseudotetragonal unit cell. BaBi4Ti4O15 was prepared by homogenization and sintering of mixture of stoichiometric quantities of barium titanate and bismuth titanate obtained via mechanochemical synthesis. Barium titanate, BaTiO3 has been synthesised from mixture of oxides BaO and TiO2 and bismuth titanate, Bi4Ti4O15 was prepared starting from mixture of Bi2O3 and TiO2, commercially available. The reaction mechanism of BaBi4Ti4O15 formation and the characteristics of BBT powders and ceramics were studied using XRD, Raman spectroscopy, particle size analysis and SEM. The Bi-layered perovskite structure of BaBi4Ti4O15 forms by solid state reaction and sintering at 1100 C. Microstructure of bismuth perovskite - layered materials exhibit plate-lit<e grains. The Ba2+ addition leads to the change in the microstructure development, particularly in the change of the average grain size. The noticed mode at 160 cm-r is ascribed to the vibration of rigid-layer modes that are typical in these layered structures where a layer makes vibrations as a whole. The mode at 280 cm-1 arises from TiO6 octahedral vibrations and represents a combination made of bending-stretching vibrations. The two modes of Bi4Ti4O15 around 537 cm-1 and 615 cm-1 change into a band in Bi4Ti4O15 (A=Ba) around 558cm-1. This fact can be due to the line-broadening of the two modes caused by the structural disorder in BaBi4Ti4O15 [3]. Hence this mode corresponds to the vibration in a -pseudo-perovskite layer. Also, the mode at 880 cm-l, whose frequency amounts 851 cm-1 in the case of a pure Bi4Ti4O15 compound, depends on the sort of ions which are embedded in the lattice instead of Bi. The most probably, these vibrations are closely related to the vibrations of the Ba-O bond.