Polar Cation Ordering: A Route to Introducing >10% Bond Strain Into Layered Oxide Films

Abstract

The 3d transition metal (M) perovskite oxides exhibit a remarkable array of properties, including novel forms of superconductivity, magnetism and multiferroicity. Strain can have a profound effect on many of these properties. This is due to the localized nature of the M 3d orbitals, where even small changes in the M–O bond lengths and M–O–M bond angles produced by strain can be used to tune the 3d– O 2p hybridization, creating large changes in electronic structure. A new route is presented to strain the M–O bonds in epitaxial two‐dimensional perovskite films by tailoring local electrostatic dipolar interactions within every formula unit via atomic layer‐by‐layer synthesis. The response of the O anions to the resulting dipole electric fields distorts the M–O bonds by more than 10%, without changing substrate strain or chemical composition. This distortion is largest for the apical oxygen atoms (Oap), and alters the transition metal valence state via self‐doping without chemical substitution.

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

“…As noted in recent work, there is a clear correlation between the spatial dopant arrangements and charge order observed in the cuprates7374. Given the dramatic differences associated with how the ordering of dopants can affect the corresponding phase diagrams both in bulk75 and heterostructures7677, this might suggest a modified phase diagram for the YBCO doped in this manner. As noted above, the deviation from linear T , which is associated with the onset of the pseudogap and associated q  = 0 magnetic order in the bulk6378, occurs at a much lower temperature and perhaps suggests a suppression of the onset of the pseudogap phase.…”

Massive band gap variation in layered oxides through cation ordering

“…Recently, A-site cation ordered LaSrNiO 4 and LaSrMnO 4 RP oxides were experimentally grown with precise atomic control using oxide-MBE techniques 40,41 . Leveraging, this approach with misfit strain from epitaxial growth or by tuning the magnitude of the cation-orderingdriven bond length modulations via large A-site valence differences offers a potentially transformative paradigm to rationally design band gaps, absorption and emission edges, or transport properties for photo-and electrocatalysis, where such layered Ruddlesden-Popper and Dion-Jacobson phases are already finding use, yet remains far from ideal.…”

Ferroelectricity from coupled cooperative Jahn-Teller distortions and octahedral rotations in ordered Ruddlesden-Popper manganates

“…It has recently been grown in the RP structure as a thin film with random occupancy of La and Sr on the A site. 34 Layer-by-layer growth of LSMO, however, also makes it possible to achieve desired A-cation ordered arrangements, 35,36 i.e., periodic LaO and SrO monoxide planes along the crystallographic direction with disconnected MnO 6 octahedra (Fig. 1b).…”