Thin-film solid-state reactions of solid BaCO3 and BaO vapor with (1 0 0) rutile substrates

Thin-film solid-state reactions in the BaCO3–TiO2 and BaO–TiO2 systems have been experimentally studied in air and in vacuum, respectively, on (1 0 0) TiO2 substrates. The solid–solid reactions in vacuum and in air showed that different processes occur during BaTiO3 formation: an intermediate Ba2TiO4 compound is always observed in vacuum but not in air. The crystallographic orientations between the reaction products and the TiO2 substrate were investigated by X-ray diffractometry and transmission electron microscopy. One orientation relationship has been found for BaTiO3 after a solid–solid reaction, whereas different orientation relationships for BaTiO3 have been identified after a vapor–solid reaction. At high temperatures, Ti-rich polytitanates were grown in both types of solid-state reactions but with quite different textures. The crystallographic relationships and their origins are analyzed.