Hydrothermal growth of BaTiO3 on TiO2 single crystals

The hydrothermal growth of polycrystalline BaTiO3 deposits on the surface of TiO2 rutile single crystals has been studied with respect to the following parameters: (a) small quantities of Sr (1.0 and 0.04 at.%) in the Ba(OH)2 aqueous solution and (b) crystallographic surface of TiO2. For this purpose, the substrates were immersed in hydrothermal baths at temperatures between 100 and 200 °C for 4 h. It was found that the deposits grown with the high purity Ba(OH)2 reagent (Sr∼0.04 at.%) exhibited grains with a pronounced crystal habit of octahedral shape with well-defined {1 1 1} faces. The grains grew at temperatures as low as 100 °C. The strontium rich Ba(OH)2 solution (Sr∼1.0 at.%) led to grains of spherical shapes, which appeared only at temperatures of 150 °C and above. The use of single crystal substrates with different orientations strongly influences the growth of the BaTiO3 layer: the same treatment to deposit BaTiO3 on the (0 0 1) TiO2 face did not produce BaTiO3 on the (1 1 0) surfaces. This result can be interpreted in term of the stability of the single crystal surfaces and the related dissolution of TiO2. The samples were characterized by means of XRD, RBS, EDX, XPS, SEM (secondary and backscattered electrons), WDS, TEM and AFM.