title: Local Crystal Structure of Antiferroelectric Bi2Mn4/3Ni2/3O6in Commensurate and Incommensurate Phases Described by Pair Distribution Function (PDF) and Reverse Monte Carlo (RMC) Modeling.
abstract: The functional properties of materials can arise from local structural features that are not well determined or described by crystallographic methods based on long-range average structural models. The room temperature (RT) structure of the Bi perovskite Bi2Mn4/3Ni2/3O6has previously been modeled as a locally polar structure where polarization is suppressed by a long-range incommensurate antiferroelectric modulation. In this study we investigate the short-range local structure of Bi2Mn4/3Ni2/3O6, determined through reverse Monte Carlo (RMC) modeling of neutron total scattering data, and compare the results with the long-range incommensurate structure description. While the incommensurate structure has equivalent B site environments for Mn and Ni, the local structure displays a significantly Jahn-Teller distorted environment for Mn3+. The local structure displays the rock-salt-type Mn/Ni ordering of the related Bi2MnNiO6high pressure phase, as opposed to Mn/Ni clustering observed in the long-range average incommensurate model. RMC modeling reveals short-range ferroelectric correlations between Bi3+cations, giving rise to polar regions that are quantified for the first time as existing within a distance of approximately 12 Å. These local correlations persist in the commensurate high temperature (HT) phase, where the long-range average structure is nonpolar. The local structure thus provides information about cation ordering and B site structural flexibility that may stabilize Bi3+on the A site of the perovskite structure and reveals the extent of the local polar regions created by this cation.
authors: Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K.
authors: Robert J
authors: RJ
authors: Szczecinski
authors: Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K.
authors: Samantha Y
authors: SY
authors: Chong
authors: Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K.
authors: Philip A
authors: PA
authors: Chater
authors: Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K.
authors: Helen
authors: H
authors: Hughes
authors: ISIS Facility, Rutherford Appleton Laboratory , Harwell, Didcot OX11 0DE, U.K.
authors: Matthew G
authors: MG
authors: Tucker
authors: Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K.
authors: John B
authors: JB
authors: Claridge
authors: Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K.
authors: Matthew J
authors: MJ
authors: Rosseinsky