Phase formation and characterization of the SrBi₂Ta₂O₉ layered-perovskite ferroelectric

Abstract

The Sr-Bi-Ta-O system is of interest for thin-film non-volatile ferroelectric memories. A better understanding of the process by which the perovskite phase forms can provide insight for improved processing of this ferroelectric compound. We have prepared thin-films by a chemical method using Sr-acetate, Bi-acetate and Ta-ethoxide; cation ratios were ∼1:2:2 for Sr, Bi, and Ta, respectively. Results of in-situ crystallization studies using High-Temperature Grazing-Incidence X-ray Diffraction (HTGIXRD) have demonstrated that a fluorite structure, forming in the ∼600 – 700 °C range, acts an intermediate phase prior to the crystallization of the perovskite. Additional samples with cation ratios of –1:0.8:2 were also investigated. Results for samples prepared with the 0.8 Bi content indicated that a pyrochlore phase forms which contains a substantial deficiency in Bi compared to the composition of the perovskite phase. The structures of the pyrochlore and fluorite phases and their relation to the formation of the perovskite ferroelectric are discussed.