RAMAN STUDY OF EFFECTS OF EXCESS BI CONTENT IN METALORGANIC DERIVED Bi{sub}4TbO{sub}12 FILMS

摘要

Bi{sub}4Ti{sub}3O{sub}12 (BIT) films with different excess Bi content (0-6 mol.%) are studied using x-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman scattering. From SEM data, the grain size and densification increases with excess Bi content, indicating that the grain growth of the film is related to the excess Bi content and liquid phase sintering occurs at 6 mol.% excess Bi BIT films. From the XRD data, the c-orientation of the BIT films increases from 0-4 mol.% and is well developed when Bi excess reaches between 4 and 7 mol.%. From the analysis of the Raman spectra, the Bi{sub}2O{sub}2 layer remains unchanged in the Bi-deficient (～0-2 mol.% Bi excess) as well as stoichiometric (～4-6 mol.% Bi excess) films; implying that during film growth, Bi first goes to the Bi{sub}2O{sub}2 layer in which the Bi site has higher stability than that in the perovskite-like slab. With increasing excess Bi, the excess Bi is incorporated into the A site in the perovskite-like slab, enhancing the distortion of TiO{sub}6 octahedra, Also the preferred film orientation becomes c-direction. A decrease of the distortion of TiO{sub}6 octahedra (e.g. by doping with a smaller ion like La) is possible and is important for improving the polarization in the c-direction of BIT films.