Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.
Bibliographical noteFunding Information:
G.S., C.-H.L., D.G.S., V.G. and N.A. were primarily supported by the Center for Nanoscale Science, a National Science Foundation center through Grant number DMR-1420620. G.S. and V.G. also received partial support from NSF Grant number DMR-1210588. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract no. DEAC02-05CH11231. T.B. was supported by the Rutgers Center for Materials Theory. C.J.F. acknowledges support from the NSF Grant number DMR-1056441. We would like to thank Marissa Libbee for her helpful guidance preparing TEM samples. We would also like to thank Roman Engel-Herbert for useful discussions and Haiying Wang with sample prep.
© 2016 The Author(s).