Oxygen octahedral tilt ordering in (Na_(1/2)Bi_(1/2))TiO_3 ferroelectric thin films

摘要

Oxygen octahedra tilt (OOT) transition is the most common type of distortion in inorganic ABO(3) compounds with a perovskite crystal structure. The importance of OOT transitions is underlined by accompanying changes in the B-O and A-O bonding environments, which consequently affects the electronic states and hence influences electrical, magnetic, and superconducting properties of many perovskite compounds. In recent years, controlled manipulation of the OOT order in perovskite thin film ferroelectrics has been attempted through heteroepitaxial strain engineering. The current study demonstrates an alternative approach whereby OOT ordering in a 200 nm thick polycrystalline thin film of (Na1/2Bi1/2)TiO3 (NBT) Pb-free ferroelectric is induced by applying electric-field along the 111 octahedral tilt axis, which is furthermore enabled by a strong (111) crystallographic texture normal to the film surface. In situ x-ray diffraction reveals that electric-field-induced OOT ordering proceeds through nucleation and rapid growth of domains with ordered a(-)a(-)a(-) tilting, followed by an increase in the tilt angle within the ordered domains.