Growth of epitaxial sodium-bismuth-titanate films by metal-organic chemical vapor phase deposition

The liquid-delivery spin metal-organic chemical vapor phase deposition method was used to grow epitaxial sodium-bismuth-titanate films of the system Bi4Ti3O12 + xNa0.5Bi0.5TiO3 on SrTiO3(001) substrates. Na(thd), Ti(OiPr)2(thd)2 and Bi(thd)3, solved in toluene, were applied as source materials. Depending on the substrate temperature and the Na/Bi ratio in the gas phase several structural phases of sodium-bismuth-titanate were detected. With increasing temperature and/or Na/Bi ratio, phase transitions from an Aurivillius phase with m = 3 to m = 4 via an interleaved state with m = 3.5, and, finally, to Na0.5Bi0.5TiO3 with perovskite structure (m = ∞) were established. These phase transitions proceed at remarkably lower temperatures than in ceramics or bulk crystals for which they had been exclusively observed so far.