Hydrothermal synthesis of barium titanate particles and heteroepitaxial thin films

The synthesis of ultrafine BaTiO3 particles by a reaction between fine TiO2 particles and a strongly alkaline solution of Ba(OH)2 under hydrothermal conditions was investigated. The influence of the synthesis temperature (80°C to 240°C) and time (1 to 96 hours) on the characteristics of the BaTiO3 powders was investigated by X-ray diffraction, transmission electron microscopy, thermal analysis and atomic emission spectroscopy. The powders were predominantly cubic at lower temperatures ( \u3c 160°C), and contained increasing amounts of tetragonal BaTiO3 at higher temperatures. At the highest synthesis temperature (240 °C), the powder consisted of a mixture of the cubic and tetragonal phases. The purity of the powders is mainly controlled by the characteristics of the starting materials and improved with increasing temperature and longer time. The powders had a relatively narrow size distribution at lower synthesis temperatures ( \u3c 160°C), and a bimodal distribution for long reaction times at 240°C. Textured heteroepitaxial BaTiO3 thin films were deposited on single crystals of SrTiO3 and LaAlO3 at 150°C using the same reactants employed for the powder synthesis but at lower concentration. The formation of the films was investigated using atomic force microscopy (AFM), a high-resolution scanning electron microscopy (SEM), and X-ray diffraction (XRD). The formation of the films occurred by nucleation of {100} faceted islands followed by growth to produce nearly complete coverage of the substrate after less than 5 hours. Thickening of the film was achieved by refreshing the reactant solution and repeating the deposition process. X-ray diffraction coupled with pole figure analysis showed that the films had the same in-plane and out-of-plane orientation as the substrate and thus, they can be considered to be textured epitaxial thin films --Abstract, page iv