TEM cross-section investigations of epitaxial Ba2Bi4Ti5O18 thin films on LaNiO3 bottom electrodes on CeO2/YSZ-buffered Si(100)

Epitaxial, ferroelectric Ba2Bi4Ti5O18 films grown on LaNiO3/CeO2/ZrO2:Y2O3 epitaxial layers on Si(100) are investigated by plan-view and cross-section transmission electron microscopy. The films consist of well-developed grai ns of rectangular shape, in the following called tiles. The boundaries betw een the tiles are strained and contain many defects. A new, specific type o f lattice defect is found in the the boundaries. This defect is described a s a staircase formed by repeated lattice shifts of Delta approximate to c/1 2 approximate to 4.2 Angstrom in the [001] direction, which result in seemi ngly bent ribbons of stacked Bi2O2 planes. The individual Bi2O2 planes rema in, however, strongly parallel to the (001) plane. Each step of the stairca se being formed by short sections of two or more Bi2O2 layers in direct con tact, the defects carry a bismuth excess. Accordingly, the the boundaries a re bismuth-rich. A model to explain this bismuth excess of the the boundari es is proposed.